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Main functions of the window: lighting, ventilation, view
( Moritz von Schwind : morning hour )
Gothic stained glass, around 1230–1235, in Chartres Cathedral

In construction, a window is a light opening in a wall or in the roof of a building , as well as its windproof and weatherproof closure. Windows are used for exposure , ventilation and views . Windows are also one of the main elements of the aesthetic structure of the facade and ideally adorn both the exterior and the interior of the house.

Today windows usually consist of a frame and the glass window filling. The frame is inserted into an opening in a wall or roof. The wall opening is usually reinforced at the top by an arch or by a lintel , laterally by the reveal or the bezels and at the bottom by the parapet . A movable window sash often enables the interior to be ventilated. Windows are traditionally manufactured and installed by glaziers , carpenters and specialized window manufacturers.


Openings in the outer boundaries of structures that are enclosed on all sides are referred to as “windows” with the purpose of enabling optical contact between the inside and outside and / or allowing light to enter . The main use of the German term is in construction. According to the definition in Part 1 of VDI 4700, windows are used for lighting and, as a rule, also for ventilation. In contrast to the door or gate , the window lacks the function of passage or entry. Windows are also used in the shells of vehicles, in plant construction and in other technical facilities. In the aforementioned subject areas, windows can be mere openings, but they are usually filled with glass or other translucent materials. They can be solid or have constructive devices for opening. In a figurative sense, “windows” are also used to describe other types of narrowly circumscribed passages in otherwise impermeable structures. In the computer field, so-called "windows" are a fundamental element of graphical user interfaces; they gave the Microsoft Windows operating system its name.


The noun window has been part of the German standard vocabulary since the 8th century. It is borrowed from the Latin fenestra , the origin of which is dark. The neutral gender probably comes from the older ouagtora for "eye gate" (round window). The old Germanic term for it meant wind-eye (Gothic windauga ), which has been preserved in the Danish term vindue and in the English window .


Wreaths or rows of windows already existed in the basilicas or the thermal baths of antiquity; With the exception of the Basilica of Constantine in Trier (4th century) , which was later changed, none of them have survived. In early and high medieval church buildings there are regular rows with uniform windows. The most important building with a preserved window wreath is the Hagia Sophia (6th century) in Constantinople / Istanbul . In medieval architecture they sometimes appear on the ambulatory, on the apses or in lantern towers.

Before-glass age

Windows covered with animal skin, Celtic Museum Mitterkirchen / Upper Austria
typical medieval "window niche" with stone: stone made of neatly smoothed stone in the quarry stone masonry , stone window sill and heavy window lintel, and a fold to attach the window fastener can be recognized

The oldest human residential or cult buildings (e.g. Göbekli Tepe ) were windowless; Light sources were the entrance and the smoke outlet in the roof. There were already slit-like openings for light in Neolithic houses. In Persepolis , window openings were found in the mud wall of a 6000 year old house. Even the residential and cult buildings of the Egyptians as well as the Greeks and Romans were largely windowless to the outside; Windows were found mainly in royal and market halls ( basilicae ) as well as in thermal baths. In Northern Europe, shop-like window locks are known from the Neolithic and the Bronze Age . Also urns of different backgrounds are designed in the form of buildings with windows ( House urn ).

Originally, windows were rectangular, arched, round or oval openings in walls that were later covered with skins , parchment or linen to reduce the effects of the weather. Mainly in sacred buildings, thin, translucent alabaster was also used in the wall openings . Since the Romanesque period there have also been three-pass or fan-shaped windows (e.g. Quirinus-Münster in Neuss ). The largest (preserved) Romanesque windows are the iron-braced west windows of the Cathedrals of Chartres and Le Mans ; in Gothic it is the windows of the English cathedrals, stabilized by rods and tracery , or the huge transept windows of the cathedral of Metz ; The west window of Altenberg Cathedral should also be mentioned in this context.

Art nouveau lattice windows :
L'atelier du maître-verrier Sterner 1904, Brussels

Beginning of the glass age

The first window glasses were found in Aix-en-Provence and Herculaneum . The finds have sizes of up to 80 cm². However, no written record mentions the manufacturing process. For the early, thick-walled and one-sided matt window glass, there are different views in the professional world on its production. On the one hand, a manual stretching technique is suspected. At the latest since the 1st century BC The Romans used glass. Initially, the panes were rough on one side and therefore not transparent. It was not until the 2nd century AD that glass appeared that had a smooth surface on both sides. In any case, north of the Alps, window glass was only installed in isolated cases, as has been the case in church construction since the 5th century. It was not widely used until the 12th century, when it was occasionally found in private homes as a special luxury. In the 15th century it was by no means a matter of course in cities either.

Window glass also serves as a carrier material for glass painting or is colored in different colors to create ornament glass and glass mosaics . Church windows have been designed with this technique since the Gothic period , and later windows on secular buildings . The manufacture of large glass panels has only been possible since industrialization. That is why window panes have been made up of several smaller pieces of glass for centuries.

Wilhelminian style facade with a particularly large number of different windows, Radebeul 1902

Founding period

In residential buildings, wooden windows in double box construction were mostly used. Industrial and other utility buildings were provided either with wooden windows or windows made of cast iron. The same standard dimensions were used regionally. After the founding period, the 20th century began with various architectural trends that tried out new design forms. In the new building , as in the more traditional style of the 20s and 30s, the facade openings were increasingly combined into ribbon windows .

New Objectivity

In residential buildings, wooden windows were mostly used as composite windows. Industrial and other utility buildings were provided either with wooden windows or windows made of steel profiles. Windows were manufactured with standard dimensions and modules in industrial production, e.g. B. the Frankfurt norms of the New Frankfurt . Installation of the sliding window, which was previously unusual in Europe.


Economic miracle

In residential buildings, wooden windows in double box construction were mostly used. Industrial and other utility buildings were provided either with wooden windows or windows made of steel profiles. Windows were manufactured industrially with standard dimensions and modules. Installation of the sliding window, which is unusual in Europe.

1954: Development of the first plastic window

Heinz Pasche developed the first plastic window together with the Dynamit Nobel company from Troisdorf. Pasche was a metal worker and wanted a plastic cover over a metal frame that was weatherproof and insensitive. At that time, Dynamit Nobel was already known for its developments in the plastics market and had various extruders . This then resulted in the Trocal company, which in 1954 brought the first plastic window onto the market in series.

1970s and 1980s

In residential buildings, wooden, aluminum and plastic windows were used as single windows with double glazing (e.g .: 4-12-4) . Industrial and other utility buildings were provided with wooden, aluminum, steel and plastic windows. Windows were manufactured industrially with standard dimensions and modules. Distribution of plastic windows.

1990s until today

The window systems differ relatively strongly in the individual countries, windows for the central part of Europe are described below:

From the mid-1980s on, insulating glass windows clearly dominated in Germany - single windows with double-pane insulating glazing and tilt and turn fittings. Metal vapor deposition on one of the two panes significantly increases the thermal insulation of the glass. Plastic windows are gaining strong market shares. In return, wooden windows are clad on the outside with aluminum frames in order to achieve the necessary weather protection. From the beginning of the 2000s, triple insulating glass was built with ever better thermal insulation, the thermal insulation of the windows was increased and enabled the construction of low-energy and passive houses. Window elements are used generously in both residential and commercial buildings, and the proportion of glass on the exterior is increasing sharply.

Large windows with insulating glazing or heat protection glazing for buildings could only be produced as flat panes until around 1990. Further developed manufacturing processes in the glass industry now also allowed curved panes, as is common in automotive engineering. Windows are no longer just wall openings, but are viewed in terms of building construction like modularized facades. Manufacturing specifications, static conditions, function and construction standards must be taken into account. The basis for a new window are usually modular systems , that is, the window profiles and accessories have already been tried and tested and matched to one another, they only need to be brought to the correct length and put together.

In modern buildings such as the Sony Center in Berlin, one often speaks of "element facades", as here windows are fitted directly to windows. Occasionally horizontally lined up windows are also referred to as "Band window" or " window strips (engl." Ribbon windows ), respectively.


Window types

Depending on the type, material and installation location of the window, a distinction is made between the following windows:

According to material
  • Aluminum windows
  • Wooden window
  • Wood-aluminum windows
  • Plastic windows
  • Plastic window with aluminum cladding
  • Steel windows
According to installation location
  • Basement window (below the ground floor)
  • Exterior window
  • Corner window, bay window with curved or frameless panes butting against one another across corners
  • Facade connection window
  • Roof window or roof window or skylight
  • Insert element in mullion / transom facades
  • Inside window to the stairwell, to the inside bathroom or other rooms
According to properties
After division

Depending on the size of the wall opening ( window lights ), the window consists of several individual elements

  • single-leaf window
  • Casement window : there are at least two movable elements; usually two side-by-side rotating blades.
  • Skylights : the upper part of a horizontally split window, often as a bottom hung sash or permanently glazed; mostly smaller than the main window.
  • Lower lights : lower part of a horizontally divided window; often permanently glazed and less high than the main window.
  • multi-sash windows , window systems or window elements ; Horizontally or vertically arranged also ribbon windows

Parts of the window

The outer frame, in which the opening sashes or fixed glazing are inserted, is now usually referred to as a frame . The peripheral frame of a movable window sash is accordingly sash mentioned.

The sash and frame are connected to one another via window fittings .

In the case of wooden windows, the frames are made up of wooden frames, which are called scantlings in their raw form . Before they are joined together to form the frame, the scantlings are usually profiled by milling rabbets or bevels, grooves and decorations and are therefore also referred to as profiles . Metal and plastic windows are now usually composed of hollow chamber profiles .

The skylight is from the main wings by a horizontal bar separately, also known as the fighter is referred to. Two wings placed next to each other are separated by a vertical post , which is also known as the set wood . If this post is dispensed with, the main sash strikes instead on the French sash , on which a so-called blow bar is often placed, which serves as an additional stop.

The profile strips that used to be used to subdivide the window sashes are known as bars . Fixed glazing installed in the frame can also be divided by bars.


  • Ribbons, window fittings , olives
  • Window sill inside and / or outside (outside also called ledge )
  • Fixed or movable sun protection and shading systems
  • Shutters are important design elements of the building facade; They also offer protection from the weather, from sight, from the sun and from burglary
  • Blinds , inside and outside
  • Blackout systems, curtains
  • Sun protection films
  • Fly screens
  • Light tube
  • Ventilation elements (which are e.g. inserted into drilled or milled ventilation openings)

Stone frame window

Subdivision according to use or form

With masonry walls, the problem arises of creating a suitable upper end of the wall opening (window soffit ) that guides the static pressure forces in the wall around the window. The materials used for the horizontal upper end ( window lintel ) must also be able to withstand the tensile stress that occurs.

Wooden beams or lintels made of natural stone were used , whereby a relief arch had to be built in the masonry above , which relieves the lintel. Windows made of ashlar with free widths of more than one meter were seldom built before materials such as steel or reinforced concrete were available.

Thermal bath window

The motif of a semicircular three-part (trichotomic) window goes back to Roman architecture , in which the window was primarily used to illuminate the thermal baths due to its size, hence the name as a thermal bath window or Diocletian's window. In Renaissance architecture, the motif already appears in the Vatican's Capella Paolina, completed in 1540 (architect: Antonio da Sangallo the Younger ) and previously - as a wall motif without a window function - in the Sigismund Chapel of the Kraków Wawel, completed in 1531 . Later the motif was u. a. Taken over by Palladio after seeing the type of window in his elevation studies of the baths in Rome . He used it equally for secular buildings such as the Villa Pisani (1560) and his Venetian churches. When the Diocletian's Baths were converted into the Church of S. Maria degli Angeli e dei Martiri , the window type was adapted for the Baroque era . Later it found particular use in classicism , in the following historicism and art nouveau .

Baroque facade of the old Joanneum in Graz made of large arched windows .

Arched window

For the larger wall openings, traditional masonry technology required real arches to bear the load of the wall above. The design of the window frames and glass surfaces as arched windows resulted from the structural shape of the wall opening.

The arched window developed from the round arch of the Romanesque over the pointed arch of the Gothic to numerous other types such as elliptical arches, basket arches and segment arches. In the Baroque , Rococo and Art Nouveau variety of window shapes were developed.

Larger windows were built from multiple arched windows lined up, separated by columns or pillars that carry the load. Such windows are z. B. the coupled arched windows of the Romanesque .

Stone cross window with slug panes and small ventilation wings

Cross-frame window

The cross-frame window , rarely also stone cross window , is the first further development to expand the window opening in height and to increase the light transmission. Adapted individual windows were used in the resulting subdivided frames. This also made it possible to divide the lighting and ventilation functions into different individual windows. Accordingly, different locking methods could be used (window sash below, fixed glazing above; often also: massive wooden shutter below, fixed wooden frame covered with thin tanned leather above). If the middle post is missing, the dividing timber is named after it ( transverse floor window ).

Gothic tracery windows

Tracery windows

The Gothic designed the windows in church buildings with additional filigree masonry, the tracery , which was built into the window opening and also took on the tasks of a stone or wrought-iron window frame. In the original design, tracery windows were designed as colorful lead glass windows and were an essential part of the Gothic room concept in sacred buildings. In the Renaissance, the window was supported by a vertical bar made of stone, in some cases by another horizontal bar, which then resulted in the so-called stone cross window. Similar forms developed in the Arab-Indian region, in which the windows are closed opaque but translucent by intricate filigree.

Stone sliding window, around 18./19. century

Stone sliding window

Stone sliding windows were mainly used in rural areas for vaulted cellar ventilation. When it was cold it was simply closed. No incidence of light was necessary. In addition to the single-sash window , multi-sash windows with or without intermediate mullions are also manufactured. In the case of double-sashed windows without intermediate mullions, the main sash , the double sash , hinges directly on the inactive sash . In the case of three-wing constructions, the middle wing can be designed as a fixed wing, as a double wing or as a single wing.

Frame or frame and casement windows

Another important development in window construction was the window frame (colloquially called "window frame "), which led to the development of the frame window . The Zargenfenster allows the separation of cane and the actual window and a clean windproof stop by executing a rebate in the frame. Up to around 1700, the window sashes struck the frame without overlap or with a single rebate, so that the sash and frame are flush with the surface.

Frame windows were attached to the dummy block , which is made of wood or stone. In the course of modern times they have completely displaced the stone-framed window by inserting a wooden frame into the stone frame. In stables and industrial buildings, frames and frames made of steel profiles, wrought iron or cast iron are also used.

A special form of the frame is the frame , which is so named because it is in front of the actual supporting blind frame . With today's dimensionally stable masonry, a dummy block is no longer required to create the wall opening. The frame is reinforced in modern windows, so that the stiffening effect of the blind frame can be dispensed with.

Because the frame of the window is made to match the sash in the carpenter's workshop, more delicate and sophisticated fittings than the previously common hinges can be installed. In addition to the tightly closing turn window , the tilt window and variants such as the casement window and sliding window are developed.

Early medieval sliding window (reconstruction) with rawhide filling

Historic windows

Lattice windows

The individual pieces of glass (panes) in the transom window are smaller than the area of ​​the window sash. Between the individual panes there are narrow rods made of wood or metal, the rungs . Since it was still difficult to manufacture large panes of glass in the 19th century, glazing was mostly divided by bars. Horizontal rungs are also referred to as bars , the vertical rungs as sapwood or, in the case of larger cross-sections, also as posts .

The structure of the window areas developed into a design element that was sometimes very elaborate, especially in Art Nouveau .

Leaded glass window

The lead glass window is composed of many individual pieces of glass. These are held together by H-shaped lead profiles that are soldered together. Lead profile can easily be bent so that almost any glass surface is possible. The individual pieces of the glass mosaics are also connected using this technique.

Slugs are small, round twisted glass panels, which are assembled with lead bars and small patches, a special form of stained glass.

Single window

The single window is the oldest version. The sashes are attached outside or inside, sometimes combined with a shutter or a louvre shutter with an expandable rung .

The single window was the rule until 1820 and the double window was only found in exceptional cases. Double-glazed, then thermo- glazed single window types have been developed since the 1950s , so that the single window is currently again the most frequently installed window type in Europe.

  • Single-pane windows are no longer permitted in heated new buildings in Germany.
  • Single window with multi-pane insulating glass (insulating glass window): common standard window

Double window

Possibilities of connection

The third important component of the modern window is the idea of ​​hinging several windows one behind the other on a frame or installing several panes of glass in a window sash in order to achieve additional thermal insulation with the resulting space.

A double window can meet higher requirements for thermal insulation, windproofness and sound insulation.

Removable front window for the winter months; common in the past, now almost gone.

Front window or winter window

The front window or winter window is an additional window construction that can be inserted in front of the actual window from the outside or from the inside during the cold season. The frame can be attached with a few screws or hooks. The front or winter window creates a heat-insulating air space similar to a tightly closing shutter.

The structure is similar to a double window. Historic winter windows are rarely seen today: "These front windows, whose practical use nobody doubts, in no way beautify the exterior of the house." The reason for this statement was probably the simple construction and the reduced craftsmanship of this purely useful windows.

In the preservation of historical monuments, inner front windows are recommended if simply glazed historic windows are to be energetically improved. Outside front windows are occasionally used when valuable building-time windows are to be protected from the weather. However, the monument value of the windows is to be assessed very highly, as this changes the view of the historical facade.

The oldest finding of double windows from 1695 can still be found today at the Upper Castle in Öpfingen near Ulm. The simple window was extended to a double window by a winter window. The window opening is closed with two single pane windows arranged one behind the other.

Box window

Box window

The two separate, rigid frames of the double window are structurally combined here. The result is a closed, box-shaped cavity between the two glass surfaces and the frame.

  • Hamburger or Grazer Fenster (also Grazer Stockfenster ): Outer sashes open outwards, inner sashes open inwards.
  • Old Berlin or Viennese box windows (also Viennese stock windows ): Both wings open inwards.

With the latter construction, the outer window must be smaller than the inner one so that it fits completely through its clear width. The advantage of the old Berlin or Viennese window is that the open window is never exposed to the weather, and that the individual windows can be less than their clear width apart - while with window sashes that open to the outside, these are open on the outside wall next to the Have to hit the neighboring window: otherwise you would have to follow a corresponding sequence when closing. The advantage of the Hamburg or Graz window is that the inner reveal remains free, which makes the window niche easy to use. Often there is the option of replacing the outer sashes with shutters (also called "beams" in Austria) during summer operation.

In the past, drawn glass was often used as window glass and was held in place in the window rebate with linseed oil window putty.

In the preservation of monuments, the conversion of historical single windows to box windows is recommended. This allows the old windows to be retained, while at the same time the thermal insulation is significantly improved. The inner window does not necessarily have to be provided with a division corresponding to the outer, historical one, which reduces the cost of the renovation.

Double frame windows

The double frame window differs from the box window in that the sashes of the outer and inner window levels are attached to a single frame so that the outer sashes open outwards and the inner sashes inward.

Composite windows

The composite window is a further development of the double window and represents the transition to the modern single window with double glazing. Both sashes are connected to one another and have a common pivot point in the window frame. This type of window has sufficiently good values ​​for thermal insulation, since the air layer between the window levels reduces heat transfer from the inside to the outside (provided that the window seal is good). To open the window, only a connected sash is opened, but the compound sash can be opened for cleaning. Composite windows were developed as early as the second half of the 19th century, but only became established after the Second World War. Since German insulating glass panes were ready for the market in 1959, composite windows have been increasingly replaced by insulating glass windows. Laminated windows are not to be confused with laminated glass .

Windows bricked up due to window tax in Southampton, England

Blind window

A blind window (also: blind window) is a niche in the wall that has the format and appearance of a window. It is either a hinted at wall opening or a later closed wall opening or an opaque window that does not allow any incidence of light.

Blind windows can already be an original part of the building if they were installed in favor of a regular facade design, because the floor plan of the building did not allow a real window at this point. However, they often arise during subsequent renovations to the interior of the building. Sometimes blind windows are provided with a painted muntin division that corresponds to that of the other windows.

Structural properties

Glass surfaces that are only used for exposure and cannot be opened are called fixed glazing or fixed glazed windows .

Types of sash opening

Swing wing

Window sashes are differentiated according to the movement possibilities when opening:

  • Rotary wing : wing with a vertical axis of rotation. Usually opening inwards for easier cleaning, in windy areas it also opens outwards due to the greater impermeability with traditional construction.
    • Reversible sash : In the case of rotary sashes with a centrally arranged axis of rotation, part of the sash flaps outwards and another part inwards. With an additional lever arm and a displaceably mounted axis of rotation or a scissor drive , it is alternatively also possible to turn the wing completely on the outside without part of the wing flapping inwards (or vice versa). Reversible leaves make cleaning the outside surface easier. If the axis of rotation is arranged in the middle, the swivel range and space requirements are reduced. Airtightness is more difficult to establish. The construction of very large window sashes is made easier. The space requirement is less than inward-opening rotary sashes.
  • Tilting sash: sash with a horizontal axis of rotation at the bottom, usually tilting inwards for easier cleaning and drainage of rainwater. Frequent function on skylight windows, which can then be placed on the lower rotating sash for cleaning or completely folded over.
  • Tilt & Turn sash : You can choose between tilt and turn functions using a lever handle or several bolts.
  • Top-hung sash : with a horizontal axis of rotation at the top, often opening outwards to prevent rainwater from entering. Outward-folding skylights were often chosen in windy areas as an alternative to the less tightly closing inward-tilting sash.
    • Swing wing : The swing wing is a folding wing, the horizontal axis of rotation of which is in the middle, so that one part of the wing opens outwards and another inwards. This makes cleaning easier. Even very large windows can be easily opened as pivoting windows and hardly limit the usable floor space in the open position.
    • Retractable sash : by means of an additional lever arm and a movable pivot axis or a scissor drive, the upper edge of the sash moves down while it is being folded up. To make cleaning the outer glass surface easier, many skylights and other outward-opening windows can often be turned completely inwards.
  • Sliding sash
    • horizontally sliding : often referred to as parallel-sliding-window, parallel-sliding-tilting door, lifting-sliding-door, lifting-sliding-tilting door, parallel-opening-sliding window or door; Allgäu windows are lattice windows with a small ventilation sash that can be moved sideways.
    • vertically sliding : Often springs or counterweights attached to cables facilitate the opening and closing of the sash
  • Folding sashes : like folding doors , usually attached to vertical axes of rotation and also articulated in pairs.
  • Louvre window : Narrow strips of glass to rotate about an axis of rotation at their narrow sides (similar to a Venetian blind ). If the slats have their own frame, insulating glass can also be used.

Inward-opening turn-tilt windows are the common standard in Germany today. They are easy to use and to clean, but require complex mechanics and increased profile thicknesses for concealed fittings. In northern Germany and the Scandinavian countries, outward-opening windows are often used, which have the advantage of being pressed against the frame when there is strong wind pressure, which reduces drafts and ventilation heat losses.
Vertical sliding windows are common in Great Britain and the USA , for example .

The operation of windows came originally sash and handle olives . Later, external rods ( espagnolette and espagnolette and espagnolette lock) were used, which made it possible to lock the window sash in three places with one hand movement. In the meantime, the rods are concealed in the fitting grooves, and corner drives can be used to lock onto several sides of the window sash at the same time.

High skylights are opened using hand levers with rods or electromechanical actuators and remote control .


The RAL Quality Association for Windows and House Doors issues guidelines for the installation of windows, which want to reflect the generally recognized rules of technology (aRdT) and are often referred to as RAL installation . Also, the ift Rosenheim is a guide to planning and execution of the installation of windows and doors out. Finally, in Part C of the VOB, the General Technical Contractual Terms (ATV) are summarized, which are primarily used by public clients when awarding contracts. Specifically, the VOB ATV DIN 18355 / 2005-01 - "Carpentry work" and a. with the installation of windows.

In historical buildings, the air humidity that arises indoors could be discharged to the outside in an uncontrolled manner through a large number of leaks. In modern airtight buildings, this is done through controlled living space ventilation . If room air flows to the outside through leaky connection joints in the event of insufficient function or in the event of a defect, larger amounts of condensate can occur in the cold season. The more airtight the building envelope is, the more important it is to make the connection joints airtight and vapor-tight. If new, highly insulating windows are installed in old building walls with poor or moderate insulation values, the humidity from the room air no longer condenses on window glass or window frames in winter, but usually on the window reveal or on other cold bridges on the outer wall. To avoid moisture and mold damage, it is advisable to insulate the reveal. Since there is usually little space available, the material used should have an exceptionally good insulation value. If the outer wall construction is not consistently capillary and open to diffusion, an additional increased vapor diffusion resistance should be achieved on the inside.

The connection of the frame to the surrounding wall opening should meet the following requirements:

  • Together with the heat-insulating building materials, which may cover the joint area, the material with which the joint is filled should at least achieve the heat transfer coefficient of the window frame so that no condensation forms on the inside of the joint.
  • The connection of the window frame to the surrounding wall should be airtight, so that if there are pressure differences between inside and outside, no cold air can enter the building and no moist and warm air can enter the joint area from the inside and cause condensation there.
  • The inner closure of the joint should be made vapor-tight so that no moisture from the room air diffuses into the joint area and condenses there. The outer closure should be made less vapor-tight than the inner one, so that any condensate that occurs can dry out to the outside.

The joint area was traditionally filled with darning wool or prepared tapes made of hemp or sisal fiber , partially impregnated in the form of a stick of tar . Today it is often stuffed with mineral fiber (as required by DIN 18355) and the outer finish is made with compression tape , which expands after unrolling and adapts to unevenness. These materials have a heat-insulating effect, but are not vapor-tight and only airtight when subjected to greater pressure. Compriband is also suitable for the outer end of the joint if the manufacturer has provided it for this. If, as in timber construction, small movements of the components relative to one another have to be expected, the vapor and airtightness on the inside can be achieved with a flexible sealing tape, which is glued on the one hand to the window frame and on the other hand to the adjacent window reveal . If the reveal surface is uneven, it should first be plastered smooth. Alternatively, storage rails are available that are screwed or glued on and in turn take up the film. In the case of narrow joints, internal vapor tightness can be achieved using elastic sealants or bituminous joint seals . Since the elasticity is limited and the joint sealants often peel off over time, especially from wooden window frames, an additional seal should be made from the inside. This can be done somewhat airtight and moderately steam-tight by simply plastering. Special plaster profiles are available that are glued to the window frame and then plastered in or serve as a stop for drywall panels or wooden strips and allow the frame wood to move a certain amount without opening an air gap. Wider joints are often covered with strips of wood or other material.

Mounting foam is occasionally used to secure and at the same time seal the connection joint. Since ordinary construction foam is often not permanently dimensionally stable, special frame foam should be used, which ensures better airborne sound insulation and durability and often consists of two components. Since frame foam is also not vapor-tight and not completely airtight, an additional inner seal should be made against the vapor diffusion. As a rule, an additional fixation of the frame with metallic fasteners or plastering is always required.

The window frame is usually fastened using expansion dowels, wall brackets or metal straps made from cranked flat steel, so-called window anchors. Special window construction screws are also used, the particularly small head of which pulls into the frame profile. A slightly smaller drill is used to pre-drill. The continuous thread of the screw cuts first into the frame and then into the stone. This has the advantage that no tension is exerted on the frame. Before the final fastening, the exact position of the window is determined by pairs of wedges pushed into the joint in opposite directions and by washer plates of different thicknesses. In order to avoid shifting and twisting of the window frame, wedging should take place immediately next to screw connections that can change the position of the frame when tightened.


Cross-section through window constructions for passive houses . A plastic window with foamed profiles (yellow), steel pipe inserts for stabilization and three circumferential sealing profiles (all black). A wooden window with pre-blinded, interchangeable wooden profiles on the outside, four-fold stepped rebate and two circumferential sealing profiles. The dividing line between the sash and the frame is shown in dashed lines.
Sectional drawing through a window latch ( espagnolette lock ). "a" denotes the faceplate attached to the left wing and "b" the faceplate of the right wing

Wood , aluminum , plastic and steel are usually used to manufacture frames and sashes ; traditionally, wrought iron , cast iron and lead were also used for glass bars.

Wood is the oldest material for windows. The good thermal insulation and ease of processing are the most important advantages. Many historical windows still preserved show that wooden windows can be well over 100 years old if they are well cared for or if there is little weathering. In exposed locations and on the weather side of the building, wooden windows age much faster. Here offers itself as the use of wood and aluminum windows to. As a rule, the load-bearing window profiles made of wood are covered with a weather-resistant shell made of aluminum, so that the cozy character of the wood is retained on the inside.

Due to their durability and good static properties, aluminum windows are mainly used in public buildings and offices. Aluminum profiles are also common for glass facades. For thermal insulation, the inner and outer shells of insulating glazing are separated by plastic bars (“thermal separation”). Aluminum windows are characterized by the following properties:

  • Aluminum is durable, robust and requires little maintenance.
  • Bauxite ore, the basic material for aluminum production, is available in sufficient quantities.
  • Aluminum can be processed and shaped very easily.
  • Aluminum windows are extremely weatherproof.
  • Aluminum windows are particularly recommended where frequent maintenance and repairs are to be avoided (glass facades).
  • In contrast to wooden windows, aluminum windows are very light and hardly burden the statics of a building.
  • Aluminum windows are not flammable.

However, aluminum windows generally have a poor ecological balance because the production is very energy-intensive.

Plastic window contained in the interior of the frame and of the wing usually reinforced with aluminum , steel or glass reinforced plastic ( GRP ). A disadvantage is a relatively large frame thickness in relation to the glass surface, which can have an unfavorable effect on the thermal gain from solar radiation (provided that winter sun shines through the window).

Steel profiles are occasionally still used for simple windows that do not require any heat or noise insulation. In versions with thermal separation, they are also used in public areas with increased stress due to their high strength.

Wooden window

DIN 68121-1 assigns different abbreviations to the basic types of glazing of wooden windows:
EV - Single glazing of window sashes with single-pane glass was common until the middle of the 20th century.
2 x EV - Two separate single windows, which were arranged one behind the other as box windows in the wall opening, were common in higher-quality buildings since the early days .
DV - The double glazing consisting of two single leaves screwed together, each of which has a single pane of glass, is called a composite window . This system spread after World War II.
IV - insulating glazing or multi -pane glass became the new standard after the oil crisis in the 1970s. In order to accommodate the typically 24 mm thick insulating glass panes , new, wider frame profiles had to be used, which were usually also equipped with a circumferential sealing profile .

When using multiple insulating glazing , it is common practice to indicate the nominal thickness of the sash profile after the prefix "IV". Usual profile thicknesses are IV 58, IV 68, IV 78 to IV 98. Any intermediate values ​​occur. Sash and frame timbers are usually made of the same thickness. The height of the profile is often indicated by the slash, e.g. B. IV 68/60.

A large number of details such as the execution of rebates, bars, faceplate, glazing and water drainage are regulated in Part 2 of the standard (DIN 68121-2).

Traditionally, Fitschenbands were used as window fittings to open the sash. Then returned for easy opening rotation or tilt windows, as with modern doors, Einbohrbänder used. Initially, three simple fittings were installed on the tilt-and-turn windows, with two levers each having to be thrown in order to switch from the turn to the tilt function. Today complex systems are used almost exclusively, in which the opening types must be changed from the window handle, which also opens the sash. These hardware systems are installed in a groove running around the outside of the sash , which, like the associated Euro rebate, has been standardized as a Euro groove .

Most window construction companies purchase prefabricated glued scantlings from specialized manufacturers who have experience in selecting suitable wood qualities and who have finger-jointing machines to produce endless wooden strips with low waste quantities. Multi-layer gluing and mechanical drying of the wood ensure that the scantlings are largely free of cracks and warpage. For windows in an exposed position, for example on the weather side of the building, scantlings with a "continuous top layer" should be selected, in which finger-jointed timber is only used for the inner layers of the glued timber profiles. Experience has shown that damage in the coating of the finished window due to changing exposure to sunlight and driving rain occurs first at the points of the finger-jointing (as well as at the joints and the horizontal wooden surfaces in the lower area of ​​the window).

To avoid damage to wooden windows, manufacturers' associations and institutes such as the Association of Window and Facade Manufacturers eV, the Institute for Window Technology (ift) Rosenheim, the Institute of the Glazier Trade for Glazing Technology and Window Construction, the Federal Association of Wood and Plastic (BHKH), Berlin and the RAL-Gütegemeinschaft Fenster und Haustüren eV created a large number of guidelines.

Impregnation and coating

Until the 1950s, wooden windows were mainly primed with raw linseed oil and painted with linseed oil paint to protect the wood from the weather. Modern coating systems reduce the maintenance effort that was usual in the past, but often shorten the durability and service life of today's windows considerably, as the impregnation does not penetrate as deeply as raw linseed oil and the coating is more easily penetrated by moisture.

Sunlight causes the lignin to break down , which can be recognized by the graying of the wood surface. Before applying a coating, the gray layer must be sanded off. In order to protect the wooden surface from UV radiation , glazes and varnishes must always be given a pigmentation .

The coating of wooden windows tends to flake off on sharp edges. DIN 68121 stipulates that all edges should be rounded off with a radium of at least 2 mm. In the past, it was customary for the window profiles to be profiled, especially on the inside of the window, which included the edges. By joining the horizontal and horizontal sash timbers with a kerf of 45 degrees, the profiling of the edge ended at the joint. Today, however, a miter cut is usually no longer made, so that either the horizontal or the vertical wing profile , which is already chamfered all around, runs straight through to the outer edge and the other profile is butted onto it. By joining the pieces of wood with an all-round rounded edge, a V-shaped incision results at the cut edges of the sash and the frame, which is visually disruptive and potentially facilitates the entry of water into the wood. These joints can be closed with putty or sealant. Over long periods of time, however, damage often occurs in the window coating at this point. In the case of listed buildings, the production of windows with so-called closed parapet joints is often required, as was customary in the past. This means more work for the manufacturer, but improves the appearance of the windows as well as their service life.

At least with softwoods, the cut edges should be sealed before the frames are glued. Especially for pine wood, it is recommended to apply joint sealer to the outer parapet joints (visible butt joints of the sash and frame timbers) after the sash and frame have been completed.

The ift Rosenheim publishes a table "Coating groups for windows and external doors", according to which a suitable coating system can be determined according to the expected weathering and the intended type of wood and coating (paint or glaze; light or dark) of the window . In this way, a lot of damage can be avoided right from the start. The "paint check" of the federal association ProHolzfenster contains a simplified scheme. In general, a three-layer structure is recommended, whereby a previous impregnation is not counted, as this does not form a film on the wood surface.

The Association of the German Paint and Printing Ink Industry published guidelines for testing paint systems and assessing damage.

Types of wood

Pine wood is traditionally often used for window construction, which due to its resin content has a somewhat better weather resistance than spruce or fir wood . Higher quality wooden windows were made from oak. In the meantime, Meranti in particular had established itself strongly. Because of the tropical wood problem , alternatives are increasingly being sought. Chemically or thermally modified woods are just as suitable as European or American plantation wood. Sun is about black locust in Eastern Europe and eucalyptus in Galicia grown.

Wood of durability class 5 should generally not be used for windows in weathered areas. Sapwood is also assigned to durability class 5.

Replica of historical wooden windows

Many manufacturers offer windows from ongoing production with particularly narrow profiles for use in historical buildings . These are often referred to as "historicizing" or as "monument protection" or "style windows". The manufacturers each use their own profiles in the width standard of IV 58, IV 68 or IV 78, which differ from one another in various points:

  • Width of the frame
  • The face width of the wing profile usually only varies slightly. There are strength deviations in the widths of the area around the faceplate and transom .
  • There is a wide range of variations in the design of the weather bar.
  • Number, type and position of the sealing profiles .
  • Occasionally, the glazing beads are only offered unprofiled. In other cases you can choose from several variants.
  • The profiling of the edges of sash and frame profiles as well as glazing beads and transoms can rarely be freely selected, although these determine the visual appearance.
  • The design of the faceplate and transom profiles can usually be selected from a few variants or freely.
  • Different options for fittings, types of glazing, coatings, types of wood and processing quality of the scantlings.

To order, you need the maximum external dimensions of the window frame (e.g. structural dimensions of the window opening) and the division of the window elements as well as the muntin arrangement with the associated axis dimensions (center dimensions of the profiles in the view in relation to the window frame). From this, the manufacturer can derive the other dimensions according to the profiles he uses. If historical windows are to be reproduced, either the dimensions of the clear width of the openings in the frame and the face width of the sash profiles or the dimensions of the clear width of the individual glass surfaces should be recorded. Often there are larger deviations, because even very narrow standard profiles can only approximate the dimensions of the historical windows. A precise comparison is advisable. Deviations from the standard profiles are usually only possible in the width of the window frame.

An exact copy of a historical window is only possible with detailed measurements and craftsmanship.

Typical design of a box window in the Wilhelminian era in comparison with a modern window in a listed design:

  • The outer face width of the wing profile was 20 - 35 mm plus up to 10 mm for the putty fillet. Modern windows often get by with 19 mm.
    • The inner face width of the sash of modern windows, including the glazing bead, is usually 54 to 60 mm. When using triple glazing, the width of the sash profile usually increases by 3 to 5 mm.
    • The glass panes of historical windows were simultaneously sealed and glued in with linseed oil from the outside. The interior view of the wing was provided with a carved profile towards the glass pane , which merged seamlessly into the front surface. Today's insulating glass panes are usually attached to the sash from the inside with a glazing bead (and then sealed with silicone from the outside). Since both the edges of the glazing bead and the window sash are chamfered during production in the machine , there is a groove between the two when the glazing bead is flush with the sash, which significantly changes the appearance compared to historical windows, even if the glazing bead has been provided with a profile ( Carbide milling or Leipzig planer ). Often only small, artisanal businesses are willing to forego the rounding of the edges. Alternatively, a wider glazing bead can be provided, which is led around the edge of the sash wood. However, the result usually deviates just as clearly from the historical view.
    • The weather protection rail made of plastic or aluminum is usually left out of historicizing windows and replaced by the traditional weather bar. Or a weather bar is at least faded in front of the rail.
    • Modern multifunctional fittings are embedded in a so-called Euro groove that runs around the sash profile from the outside. Narrow window profiles are significantly weakened by this groove. This is partially compensated for by widening the profile in depth (e.g. IV 68 and IV 78 instead of IV 58). Especially with small window formats, the sash profiles, which are widened in depth, often appear oversized. The sash is locked using movable pins that slide behind strike plates that are screwed into the associated Euro rebate . Due to the restriction to only the turning or only the tilting function, the Euro groove and rebate can be omitted. This can u. a. Realize transom face widths of around 130 mm, which come closer to the historical windows. The window is then locked using espagnolette or push rod locks .
    • A weakening of the sash can also be avoided by grooving the sealing profiles that are customary today in the frame wood instead of in the sash. Modern windows with narrow face widths are offered with one to three sealing profiles. The insulation value of the window can be increased (slightly) with the additional sealing profiles. A sealing profile that sits as far inside on the sash as possible is advantageous in rooms with high levels of humidity in order to avoid condensation in the rebate between sash and frame.
  • Width of the frame is 55 mm. Modern windows have frames that are 55-75 mm wide. The lower frame wood is often provided on the outside (or on both sides) with a rebate and a drip nose to improve the water drainage onto the window sill (sill rebate, window sill groove or connection milling) .
  • The edges of sash and frame profiles were usually only slightly broken on the outside of historical windows, often hardly noticeable. Only the horizontal edges of the wing and weather bar, which are most stressed by solar radiation and running rainwater, have been clearly rounded off. Since today's coating systems build up a higher tension than (linseed) oil paints, the DIN demands that all edges be rounded to prevent the paint from cracking at the edges. This is less relevant on the inside of the window, but it is carried out almost consistently.
  • In the past, bars were always designed to divide glass . The external face width was often only 8 mm. In addition, there was just as much for the putty bevel on both sides. Today the so-called Viennese bars are glued on both sides of the glass and the space between the insulating glass is filled with a strip that visually corresponds to the pane composite. Widths of 20 to 30 mm are common.
  • In the past, the width of the timber was often 40 to 50 mm, so that together with the upper and lower wing, there was a total face width from about 110 mm on the outside. With modern windows, less than 127 mm can rarely be achieved. With turn-tilt fittings or tilting function of the skylight or the use of triple glazing, the value often increases to 145 mm.
  • In the past, the skylight was often fitted with delicate tilt fittings (fitting straps or hinges) or the lower rebate was designed in such a way that the upper wing could be tilted over the main timber without slipping. The locking and tilt protection was done by so-called window scissors and the locking by cam .
  • The faceplate area of double- sashed windows, including the sash profiles, is usually 84 to 94 mm wide on the outside of modern windows.

Burglary, breakthrough and breakout protection

General requirements

Glazing above a certain fall height, if there is no corresponding fall protection, must be designed in accordance with the technical rules for the use of fall protection glazing (TRAV). The difference in altitude is known as the TRAV height and varies from state to state. It can be found in the respective state building regulations (LBO). The glazing is usually structured in such a way that single-pane safety glass is used on the inside and laminated safety glass on the outside. In buildings from which people are not allowed to break out ( prisons , closed hospital wards and the like), it is necessary to use suitable measures to make the windows escape-proof. Here, too, laminated safety glass is used on the one hand, and fittings with increased strength, lockable or removable handles and straps with protection against being unhooked on the other.

Tempered safety glass

The manufacture of thermally toughened single - pane safety glass (ESG) includes a special heat treatment. A pane of glass is heated evenly to> 600 ° C within a few seconds and also cooled quickly. The characteristic stress distribution caused by the heating causes a break in small, blunt-edged pieces of glass. In addition to safety, ESG offers greater resistance to bending, impact and impact compared to conventional glass panes. ESG is used in many different ways, for example in swimming pools and gyms, or as a transparent element in fire protection cladding, showers and balcony doors.

Laminated safety glass

In contrast to ESG, laminated safety glass (VSG) offers increased protection. The manufacture of laminated safety glass includes the creation of a crystal-clear composite of glass plates and plastic films. This causes a reduction in the formation of splinters in the pane in the event of destruction.

Building physical properties

For the physical properties of historical windows, see also: Window repairs


The tasks of windows are closely linked to the physical properties of these building elements. But the tasks are partly diametrically opposed. In this way, they should ensure natural exposure, but also avoid glare for the user. For each type of room use there is a calculation key that regulates the required natural lighting. Solar gains can also be realized through windows, which reduce the energy consumption when heating buildings. However, the solar energy supply should also not become too large, otherwise cooling may be necessary. With openable windows, natural ventilation can also be defined as a task.

From a building physics point of view, windows primarily represent weak points in the building envelope. In order to minimize the negative effects of the windows, the careful design of the window construction itself as well as its connection to the room-enclosing elements are necessary.

The following physical building requirements must be taken into account:

  • Definition of the position and proportion in the wall construction,
  • Resistance to weather from outside,
  • Resistance to stress from inside water vapor,
  • mechanical strength to absorb external mechanical loads (wind load, break-in, shelling),
  • mechanical strength to absorb mechanical loads from the inside (breakthrough or breakout protection),
  • Heat protection,
  • Soundproofing,
  • Glare protection,
  • Fire protection. Special fire protection glasses as well as special and tested frame constructions are used, see fire resistance .
  • Privacy screen. The privacy protection, for example, through mirroring, frosted glass or ornamental glass, the view release is regulated by law (workplace directive ).
Window of an old Rosental wooden house, Carinthia, Austria

Windproofness and air exchange rate

Historic wooden windows guaranteed a change of air . This ensured the hygienic minimum air exchange so that the mold problems that frequently occur today were avoided.

Rubber lip seals, which guarantee a very high level of airtightness, are now standard. Sufficient ventilation is no longer guaranteed without opening the window, which is why mechanical ventilation systems are increasingly required in single-family homes.

The room is usually dehumidified by ventilation . If this is not sufficient, moisture in the room air can condense on cold components . In single-glazed windows, the glass pane is the coldest surface and the humidity is visibly reflected on the pane. If such a window is replaced by a modern, thermally insulated window, it is very likely that the coldest spots / surfaces in the room will be elsewhere, for example on thermal bridges around the window frame, which will get wet and tend to mold .

All these features are checked by accredited test institutes (e.g. Institute for Window Technology (IFT) in Rosenheim ).

See also: storm hook


For the sound insulation of historical box windows, see also: Window repairs

Windows as the weakest link reduce the sound insulation value of heavy external walls considerably. The attenuation of the sound insulation value of the wall is calculated in building physics in a formula with a decadic logarithm. The noise level of road traffic can be recorded in tabular form in order to determine the necessary sound insulation value of the window.

Laminated glass panes with special sound-absorbing foils increase the internal damping of the pane so that the sound insulation level is increased. A few years ago the space between the panes was filled with a gas that is heavier than air, for example SF 6 . However, because of its ozone-damaging properties, SF 6 is now banned in most European countries due to the Kyoto Protocol for climate protection. Instead, argon or krypton are now used.

Further improvements in sound insulation can be achieved through:

  • increasing the mass of the window pane and frame
  • the combination of a thicker and a thinner pane of glass
  • Increase the distance between the discs
  • Multiple sealing levels between sash and frame made of rubber profiles

Thermal properties

In addition to the type of glazing, the design of the sash and frame are decisive for the energy balance of the window. The thermal insulation of today's window constructions, however, no longer depends as much on the material of the sash and frame as it did before, since the inside and outside of steel and aluminum profiles are also thermally decoupled by plastic inserts . Overall, however, the windows can still represent a weak point in the thermal envelope of the building, even if the mismatch between the heat loss coefficient of the window and the outer wall has become very similar. The solar heat gains from windows during the heating season and the savings in electrical light through natural lighting have a positive effect on the balance. The production of glass, aluminum, steel and plastics is very energy-intensive, and the use of tropical woods is problematic. The energy balance of the window component should not be assessed entirely without including the heating system.

The use of coated multi-pane insulating glass (MIG) is standard today. This is the only way to meet the requirements of the Energy Saving Ordinance (EnEV). An additional improvement is possible through:

  • Insulating glass window with triple glazing, which places higher demands on the window construction due to its thickness and weight.
  • Insulating glass window with a third pane in front of it: This construction is comparable to a composite window in which one pane is replaced by insulating glass. Blinds can be placed in a protected space in between.
  • Insulating glass box window: Structure like a classic box window, only that the two partial windows do not contain a simple pane, but an insulating glass pane.

Insulating glass has a limited lifespan. DIN 18545-1 (sealing of glazing with sealants; requirements for glass rebates) allows a low leakage of the sealing of the gap. Blindness or even the formation of condensate between the panes is rather rare. A lifespan of 30 years and more is not uncommon.

As a stopgap measure to improve the insulating properties of single-glazed windows, special foils are offered that are glued all around the sash and then stretched by dampening so that they are barely visible.

Thermal insulation glazing

The individual panes of an insulating glass window are connected to one another with a gas-tight edge bond made of glass spacer and sealing compound ( multi-pane insulating glass ). There is air or noble gas ( argon , krypton or xenon ) in the space between the panes . Together with vapor-deposited layers to reflect thermal radiation , it has been possible to reduce the heat transfer coefficient from 3.0 W / (m² · K) for early insulating glass to 0.9 for double thermal insulation glass and 0.5 for triple glazing . With double-pane heat protection glazing, energy losses can now be reduced to a fifth compared with single-pane glazing, and with triple-pane heat protection glazing it can be reduced to a tenth. The heat loss in conventional insulating glass panes is made up of 2/3 heat radiation and 1/3 convection. With the use of heat protection glazing, so-called Low-E-Glass (Low-Emissivity-Glass), these heat losses can be greatly reduced. If argon is used as the gas, this loss is even lower.

So-called thermal bridge losses also occur along the glass pane (see U values ). These can also be achieved through the use of suitable glass spacers, such as. E.g. warm edges can be minimized (see glass spacers )

Due to the higher weight and to avoid shear stress in the edge bond of the thermal insulation glazing, the frame must be more stable than a frame for single-pane glazing. The frame should have a similarly low thermal resistance as the glazing used. In the case of highly insulating glass, the frame and, in the case of poorly insulating glass, the glazing has the lower thermal resistance.

U-values ​​of a window

The total heat transfer coefficient of a window is made up of the U-value of the glass and the U-value of the frame. The following terms are used:

The U-value is given in W / (m² · K). The total Uw value of a window is calculated from three different factors: from the Uf value, the Ug value and the transition area between the glazing and the frame, this value is referred to as the thermal bridge loss coefficient Ψg (pronounced: psi) of the glass edge. In addition, the window size must of course also be included in the calculation.

The following applies: the lower the Uw value, the better. A window with a Uw value of 0.8 W / (m² · K) or better can be described as a passive house window.

Requirements of the Energy Saving Ordinance EnEV

In Germany, various technical parameters (U W value, g value, g tot value, orientation and inclination) of the transparent components such as windows and doors of the building under consideration flow into the EnEV verification . The transmission heat loss and the solar heat gains are used to determine the energy balance according to DIN V 18599 . Furthermore, a standard-compliant natural exposure must be proven. If proof of summer heat protection is not achieved through the planned windows, external shading elements must be provided.

Glass facade

By emphasizing the thermal insulation properties of the window, its functionality for illuminating the room has been restricted when renovating old buildings. This results from two causes:

Frame portion:

Due to the standardization of window profiles, larger windows and higher demands on thermal insulation and tightness, the window profiles that are common today are relatively large. This means that more and more glass area is lost in relation to the structural dimensions of the window. This can be seen particularly clearly with small, modern plastic windows on historical buildings, for example narrow side windows of bay windows: the glass surface here is often only a third of the wall opening.

Increased reflection:

At the interface between air and glass, around 4% of the incident light is reflected at perpendicular incidence , but significantly more when inclined at an angle. A pane of glass reflects about 8% of the incident light because of two interfaces. Double glazing already loses 15%, triple glazing even 22% of the incident light. Coating the glass surfaces can increase the reflection to around 29%.

In new buildings, however, this effect can be compensated for by large glass pane dimensions and a larger proportion of glass area. The quantitative relationship between the type of window or glazing and its ability to provide thermal insulation is described by the heat transfer coefficient .

Airtight windows

In addition, the EnEV requires a permanent, airtight building envelope. That is why modern windows have to be tight. The test of the building envelope for any air permeability can be carried out with the help of a so-called air permeability measurement. It is also known as the blower door measurement .

Historic windows can be exempted from the requirements of the Energy Saving Ordinance, see Window repairs # Window repairs and the Energy Saving Ordinance .

Passive house window

Windows that have a Uw value of 0.8 W / (m² · K) or better can be designated as passive house windows. These values ​​are often achieved by using triple glazing in conjunction with a special glass spacer.
You can read more about glazing under the article Multi-pane insulating glass .

Glass spacers

Glass spacers are mostly made of aluminum and keep the panes at a distance. For passive house windows, stainless steel edge seal systems are often used, which are additionally coated with plastic. Composite plastics known from dentistry are also used for this purpose. These special spacers are called warm edge in technical jargon .

The improved Uw values ​​of a window are also influenced by other factors:
  • Thickness of the profile
  • Number of chambers (for plastic windows)
  • Glazing rebate
  • 3. Center seal
Ventilation concept required

When using passive house windows, architects and builders have to develop their own ventilation concept. For this purpose z. B. find a so-called all-in-one heating technology use. If you build as a private person, you can do without such a ventilation concept. However, you should then remember to ventilate more often.

Solar heat gain

Energy gain , as not only heat is lost through glass, but energy is also captured when the sun is more favorable. This type of passive solar energy use is quantified by the energy transmittance (g-value). This effect is used in winter with generously dimensioned south-facing glazing, when the sun is flat and shines directly into the room. On the other hand, in summer, when the sun is steep, these glass surfaces have to be shaded by canopies, external blinds or double facades to protect the rooms from overheating. On the north side, the window area should be kept small, e.g. E.g. through skylight windows, since no solar heat gain is possible here.

Summer heat protection

Sun protection as protection against overheating in summer, this is particularly important with a large proportion of windows facing south and typically also in winter gardens .

A heat-insulating glass is a disk with a highly reflective coating. This can consist of metal vapor deposition or a sun protection film that is usually glued on afterwards .

External blinds are often used as effective shading elements. Internal blinds are not effective heat protection, but privacy screens. Balconies or canopies above the respective window protect against direct summer sunlight and thus against overheating, if dimensioned correctly.

The use of switchable glasses enables an automatic or user-controlled change in the light and energy permeability of glazing and thus an adaptation to the intensity of solar radiation.

KfW funding programs

The KfW funding programs are sometimes aimed at improving the thermal insulation of windows. Construction work is funded with discounted loans or grants. Funding can be applied for by private individuals as well as housing companies or municipalities. There are various funding programs for this, which can be requested from KfW itself.

Windows in different countries

In the United States, the kitchen sink is traditionally always installed in front of a window.

Houses in the Netherlands , Great Britain and the United States have traditionally often been fitted with sliding windows with two sashes in a horizontal format. Modern variants are mostly made of PVC , less often of GRP or aluminum. They can often be tilted for ventilation and usually opened for cleaning.

United States


An American peculiarity is that windows that can be opened and are intended for ventilation are regularly equipped with permanently installed fly screens . This is particularly easy with sliding windows. In the case of hinge windows that open outwards, a crank mechanism enables the window to be opened and closed. Another feature is a high prevalence of Hung Windows - vertical sliding windows - which owe their popularity among other things the fact that here in the hot season a mobile air conditioner or window fan can be mounted. Much more common in the USA than in Central Europe are window crosses (now purely decorative).


The US has very different climates, each with a different window being suitable.

The frames today are mostly made of PVC ( vinyl ), wood, fiberglass, aluminum or combinations of these materials. With wood clad frames , a wooden core is made weatherproof and light-resistant from the outside using aluminum, PVC or fiberglass. For wooden frames, the preferred type of wood depends u. a. on the climate of the respective region.

The different materials not only determine the appearance, durability and thermal properties of the window, they also support different designs. Fiberglass and aluminum have greater stability than PVC and wood and are built into frames that are particularly slim.

Aluminum frames have been used in the United States since the 1930s. They are typical of mid-century architecture, but are still used today in houses in the modern-contemporary style. Unlike PVC frames, aluminum frames are very slim and have no visible seams. The surface can be anodized , enameled ( baked enamel coated ) or color coated ( powder coated , paint coated ), whereby the color coating begins to dissolve after a few years. If the surface treatment is missing or poor, aluminum frames will corrode over the years. Due to their high mass, aluminum frames provide better sound insulation than PVC frames, but due to the high thermal conductivity of the material they are less energy efficient and more suitable for warm regions; For cold winter regions, however, aluminum frames with a thermal barrier ( thermal break ) are offered. Windows with aluminum frames are a good 30% more expensive in the USA than those with PVC frames.

Since a considerable part of the residential buildings in the USA are built in historicizing styles to this day, windows are very often supplied with window crosses ( muntins , glazing bars , sash bars ) - matching the respective style - which are now usually purely decorative, interrupt the glass pane virtually, but not physically. Plastic grilles that are supposed to imitate window crosses are also called grilles .


Modern windows in the United States have at least double and often triple glazing, with triple glazing being particularly beneficial in cold winter regions. The cavities between the panes of glass are mostly filled with argon , and less often with the more expensive krypton .

Thermal properties

The USA is a country with extremely different climates. In order to make it easier for buyers to find the most suitable windows for their climate zone, these are appropriately identified as part of the Energy Star program. In winter cold zones (climate zones 5–8) the panes should let in heat radiation, but ideally not let them out again. In climate zone 4, windows should help to keep the house warm in winter and cool in summer. In climate zone 3, protection from heat is paramount, but the windows must also be able to retain heat in winter. In the southernmost zones, the main requirement is to keep away from thermal radiation. These characteristics are achieved, among other things, by a special coating on the glass. The U-value ( U-factor , heat permeability) should be a maximum of 0.4 up to 0.27 depending on the region, the g-value ( Solar Heat Gain Coefficient , SHGC) depending on the region a maximum of 0.25 up to at least 0.32.

Opening types

Most Popular Window Types in the U.S. (Exterior)

Many types of windows are in use in the United States, some of which are uncommon in Central Europe. A distinction is made among other things:

Sliding window
Double Hung Windows
The most common type of window in the United States: vertical sash, portrait format, two sash. The lower wing ( Engl. Sash ) can be pushed upwards; unlike a single hung window , the upper sash can also be pushed down. With newer windows it is possible to fold both the upper and the lower sash inwards for cleaning.
Single Hung Windows
Like Double Hung Windows , but the top wing is immobile. This type of window is no longer commercially available, but still occurs in old buildings.
Sliding Windows
Horizontal sliding windows in landscape format with one sash that can be slid to the side while the second is immovable. With a little effort, many sliding windows can also accommodate a mobile air conditioner.
Hinged windows
Windows in Home Improvement Store 02.jpg
Windows in Home Improvement Store 03.jpg

Window crank on the inside of a modern casement window . When the window is closed, it is folded to the side.
Casement Windows (casement windows)
Rectangular hinge windows in portrait format, the sashes of which are folded to the left or right (usually outwards). In addition to single-sash versions, there are combination windows with two sashes separated by a set of wood. Many casement windows are opened and closed with the help of a crank mechanism , which has the advantages over manual operation that firstly the open sash is fixed in the selected position and secondly a fly screen can be used.
Awning Windows ("awning window")
Rectangular hinge windows in landscape format with a single sash that is folded upwards (outwards; maximum approx. 45 degrees). Awning Windows are usually cranked up and down, especially when they accommodate a fly screen. Awning Windows are mainly used in higher wall areas where windows are relatively difficult to reach and operate. Awning Windows are also popular in rainy regions, where they can be kept open when it rains without moisture getting into the house.
Hopper Windows (tilt window)
Rectangular hinge windows in landscape format with a single wing that is folded down (inwards; maximum approx. 45 degrees). Hopper Windows are mainly used as basement windows. Because the window opens inwards, a fly screen can be installed behind it.
Immovable windows
Picture Windows and Panorama Windows
Very large windows that often take up the full height of the room and should offer an unobstructed view of a particularly attractive area at a suitable point. A picture window is a single window that is embedded in the wall like an oversized picture frame. Picture Windows and panorama windows only have a minimal frame, can usually not be opened and therefore offer no ventilation. In residential buildings, very large windows were part of the inventory of forms, especially of the mid-century modern style.
Arch Windows
Arched windows are still often installed in colonial- style houses today. Often these are accent windows that let in light and look good, but not meant to be opened. Other arched windows combine sliding or hinge windows with an arch above. Arched windows are not standard hardware stores, but can only be obtained from special manufacturers.
Other Shaped Windows
Nowadays, non-rectangular windows are common in DIY stores with round, oval and octagonal shapes. Mostly these are pure accent windows that let in light but cannot be opened.
Transom Windows
Windows installed directly over a door or other window. In historicizing architectural styles, such windows are used up to the present day. Usually they cannot be opened.

Special forms

Multipart windows
Bay Windows
Three-part windows, the surfaces of which are offset from one another by 15, 30 or 45 degrees depending on the depth of the bay. The middle part is usually wider than the two outer ones. Bay Windows can increase the area of ​​the room (then one speaks of Oriel Windows ), but in many cases the expansion of the room only begins at the height of the window sill. Bay windows were particularly popular in Victorian architecture and are still used in colonial- style houses to this day . They are therefore still commercially available today. The side panels are now often hung windows that can be opened. Variants are bow windows: multi-part windows, often with curved panes that let in light on a curved wall, and garden windows that protrude from the house wall to provide room and sunlight for indoor plants.
Venetian Windows (Venetian Windows)
Mirror-symmetrical three-part windows, the central part of which is crowned by an arch, while the flanking parts are lower. Venetian windows were style-defining elements in many directions of Victorian architecture and are still used in colonial- style houses today . They are not common in hardware stores, but can only be obtained from specialist dealers. In today's products, the middle section occasionally consists of a double hung window with an attached arch.
Special shapes
Skylights (roof windows)
The width of pitched roof windows in the United States is determined by the rafter spacing , which is 12, 16, or 24 inches depending on the region . In order not to unnecessarily interrupt the rafters, mostly upright windows are installed. Their wings are either rigid or can like a Awning Window or casement window to be opened. Depending on the sloping roof, different types of installation and product types are selected ( curb-mounted vs. deck-mounted ). In spaces which are separated from the roof by a low attic space can light pipes ( Tubular skylights ) are installed; the daylight is fed in here through a tube.
Egress Windows
Basement windows (sliding or hinge windows) that are set up as an escape route for emergencies. Unlike a normal basement window (usually a hopper window ), an egress window lets you open so wide that a person can climb through. The short shaft ( egress well ) in front of the window can be equipped with several steps.
Storm Windows
"Storm windows" are windows that are placed outside or inside on an (insufficient) existing window for thermal or acoustic improvement. The assembly is permanent or seasonal. Although the name suggests this, Storm Windows are not used to prevent storm damage in hurricane regions either.
Witch Windows
Witches Windows (also Vermont Windows ) are windows that are installed on the gable side of a house parallel to the sloping roof, i.e. at an angle. The purpose of the inclined installation is to maximize the use of space on the narrow gable wall that separates two parallel roof lines. Witch Windows exist almost exclusively in the state of Vermont and there almost exclusively in old buildings.
Glass Block Windows
Glass block windows have been used in the United States since the early 20th century. Even today they are mainly used in bathrooms, where they should let in light but not glances. Both because of their appearance and because they do not offer ventilation, they are now often considered obsolete.


  • Bad luck, Anton: window . In: Building Constructions . 1st edition. tape 11 . Springer, 2006, ISBN 978-3-211-21500-5 .
  • Selbmann, Rolf: A cultural history of the window from antiquity to modern times . 1st edition. Dietrich Reimer Verlag, 2009, ISBN 978-3-496-01409-6 .
  • Uhlig, Günther: Windows - Architecture and Technology in Dialog . 1st edition. Vieweg + Teubner, 1994, ISBN 978-3-322-83910-7 .

Related topics

An arched window in front of a wall painting showing Salvador Dalí on a house wall in Lima ( Peru )

In Tuscany , during the Great Plague , some inns had wine windows ( buchette del vino ) through which paying guests could be served alcoholic beverages without a great risk of infection.

Web links

Commons : Window  - collection of pictures, videos and audio files
Wiktionary: Window  - explanations of meanings, word origins, synonyms, translations
Wikiquote: Window  - Quotes

Individual evidence

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  2. ^ A history of Windows., October 2015, accessed February 4, 2020 .
  3. Elmar Seebold: WISE - etymological dictionary of the German language . 25th edition. De Gruyter, Berlin / Boston 2011, ISBN 978-3-11-022364-4 , pp. 287 .
  4. see also: Finestre impannate
  5. Article on Roman window glass., accessed on February 1, 2020 .
  6. a b Institute for Historical Regional Studies at the University of Mainz Archived copy ( memento from July 15, 2016 in the Internet Archive )
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  11. ^ Marion Kaminski: Venice. Art & architecture. Cologne 2005, p. 358 and Jeanette Kohl: Architecture of the late Renaissance in Venice and in the Veneto. In: Rolf Toman (ed.): The art of the Italian Renaissance. Potsdam 2007, p. 162.
  12. see the website of the Rottweil wood manufacturer ( memento from February 24, 2015 in the Internet Archive ), accessed in February 2015.
  13. ^ Theodor Krauth: The entire building joinery. Leipzig 1899, p. 155. (Edition of 1891 online at , p. 132f.)
  14. According to EnEV 2014, Annex 3 (to §§8 and 9) the requirements according to table 1 line 2 must be observed. I.e. a U-value of at most 1.3 W / (m² · K). However, single glazing has a heat transfer coefficient of over 5 W / (m² · K). Ordinance on energy-saving thermal insulation and energy-saving system technology in buildings (Energy Saving Ordinance - EnEV)
  15. ^ Th. Kraut, FS Meyer: Das Schreinerbuch. 1891, p. 134.
  16. Mila Schrader: Windows, glass and fittings as historical building material - a material thread and guide . EDITION: elsewhere, Suderburg 2001, ISBN 3-931824-04-7 , p. 68.
  17. Tobias Huckfeldt, Hans-Joachim Wenk: wooden windows - construction, damage, renovation, maintenance. Cologne 2009, p. 295.
  18. Richard Bermpohl, Hans Winkelmann: Das Tischlerbuch. Gütersloh 1952, p. 411.
  19. ^ F. Fink: The joiner or joiner and the fine carpenter. Practical handbook and auxiliary book for building joiners, carpenters, architects, manufacturers and building craftsmen, as well as for building and trade schools. Leipzig 1877.
  20. ^ Hermann Klos: composite windows. Not yet a case for the Red List. In: Restorer in the craft. 2/2009, pp. 29-34. ( ( Memento from March 3, 2014 in the Internet Archive ))
  21. a b Senkklappscheren , In: Accessed May 2020
  22. a b Klaus Hermann Ries: VOB ATV DIN 18355 - carpentry work ( Memento from April 20, 2010 in the Internet Archive ) - "Assembly foam is no longer VOB-compliant", In:, January 22, 2005 with updates until January 27, 2008 ; from saved in April 2010. The last saved version ( memento from January 25, 2016 in the Internet Archive ) of the website is from January 2016.
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  24. a b How monument protection works in window construction - renovation with a concept , BM online, November 2014.
  25. ^ A b Klaus Hermann Ries: Installation of Windows ( Memento from September 21, 2015 in the Internet Archive ), In:; from saved in September 2015. The last saved version ( memento from January 25, 2016 in the Internet Archive ) of the website is from January 2016.
  26. If necessary, the rails themselves must be sealed to the subsurface using elastic sealing compound or plastering.
  27. Vademecum window systems - Instructions for the conversion to EnEV-compliant constructions - , Chapter 1 - Window systems, iBAT - Institute Society for Operational and Work Technology of the Carpenter Handicraft, May 2012.
  28. Wooden windows, designation of the frame profiles, In:
  29. Martin Klingelhöfer: Vademecum window systems - Instructions for the conversion to EnEV-compliant constructions - , Chapter 7 - Fittings, iBAT - Institute Society for Operating and Work Technology of the Carpenter Handicraft, May 2012.
  30. See u. a. the "Additional Technical Contractual Conditions (ZTV) for the tendering of windows" and the " Notes on the Additional Technical Contractual Conditions (ZTV) for the tendering of windows ", as of April 2010, In:; accessed in August 2019.
  31. Tobias Huckfeldt, Hans-Joachim Wenk: wooden windows - construction, damage, renovation, maintenance. Cologne 2009, ISBN 978-3-481-02504-5 , p. 54.
  32. Richard Bermpohl, Hans Winkelmann: Das Tischlerbuch. Gütersloh 1952, p. 403.
  33. Hermann Klos, Günther Seitz: The historical window. In: Klaus Könner, Joachim Wagenblast (Hrsg.): Stand firm my house in the world brew. Monument preservation - conception and implementation. State Monuments Office Baden-Württemberg and City of Aalen, Aalen 2001, p. 215.
  34. Peter Struhlik: Total loss of 700 windows , published in the magazine "glaswelt 11.2009", In:
  35. ^ Ulf Hestermann, Ludwig Rongen: Frick / Knöll building construction theory. Part 2, Springer Vieweg, Wiesbaden 2013, ISBN 978-3-8348-1617-7 , p. 437. (
  36. ProHolzfenster eV Initiative: Recommendations for factory finished treatment of windows and doors made of wood , In:, as of March 2003. As well as the older edition from November 2002: Recommendations for factory finished treatment of windows and doors made of wood , In: Sikkens; or alternatively: Recommendations for the factory-finished treatment of wooden windows and house doors ( Memento of January 4, 2006 in the Internet Archive ), In:, as of November 2002.
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  38. Note the coating group table - Tips for coating wooden windows , In:, February 4, 2003 BM online 02 | 2003
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  42. The information on the modern, so-called "historicizing" or "monument protection" or "style windows" comes mainly from the technical drawings of the PaX Classic GmbH company and the Zimmer carpentry from Pirna from July 2019.
  43. Depending on the width of the wall stop and the thickness of the plaster, the outer frame can no longer be seen from the outside after plastering. However, a face width of up to 30 mm is also common. The face width of the lower frame wood was often even larger; It was often clad with zinc sheet to protect it from splashing water.
  44. This dimension can be reduced by up to 15 mm, depending on the manufacturer. The width often results from the hinges of the tilt and turn fittings. Narrower frames are possible if traditional fitschen bands or modern concealed hinges are used.
  45. Entry sill fold in the "Bauhistorisches Lexikon": "Special fold on the underside of the outer sill, designed as a water nose for draining rainwater." (Term 4203 from 02/21/2008 - 13:49:00); Elsewhere Verlag GmbH, publisher for exclusive building themes
  46. , overview of safety glass
  47. , information about laminated safety glass
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  54. Ventilation concept for passive houses
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