Outer wall
The outer wall is the wall of a building that separates the exterior from the interior . She also takes on other tasks. In architecture , as a facade, it is also an important design element of a building.
Functional requirements
Thermal insulation
Thermal insulation is the protection against cooling down of the building and living hygienic requirements and at the same time heat storage through the use of heavy building materials with a high density class . In general there is a temperature difference between the inside and outside of buildings . Inside the building, the temperature should correspond to the wishes of the user, but outside there is a temperature corresponding to the current weather . Without measures, the inside temperature would follow the outside temperature with a delay and smoothed out somewhat.
The measures to maintain the internal temperature ( heating , cooling ) usually require energy expenditure, and the less the outer wall conducts heat ( thermal insulation ). In order to achieve sufficient thermal insulation, the wall properties that are required for the statics are usually not sufficient. That is why building materials are often used that contain air inclusions (e.g. bricks with a low bulk density class ) or a combined wall structure made of a heavy supporting shell of a high bulk density class, thermal insulation materials, e.g. B. as core insulation or thermal insulation composite system and weathering layer ( plaster , facing masonry or curtain-type, rear-ventilated facade ).
The temperature on the inner surface of the outer wall is lower than the room temperature in winter, because heat flows out through the outer wall and this heat has to be supplied by the heat flow from inside the room. Since a temperature difference is always necessary for a heat flow, the temperature of the wall surface is lower, with the exception of wall heating ( envelope surface temperature control ). The temperature at the heating location (e.g. hot water pipe) is then higher, so that from there the temperature drops to both sides.
The Energy Saving Ordinance exists in Germany for the maximum energy requirement to maintain the internal temperature under standard conditions (not under local conditions) .
Solar profit
But a wall also absorbs energy from solar radiation . Thermal insulation reduces this gain - but also reduces the transmission heat loss. Since the heat loss in winter is greater than the solar gain, the difference (heat loss - solar gain) is reduced by the same percentage, and therefore insulation saves heating energy.
A scientific study by the engineering office for building physics ALware shows how much the heat storage mass of a house saves heating energy. Using the example of a KfW 40 house, it examined the energy savings and summer heat protection of various construction methods. The study on the thermal indoor climate comes to the result that heat storage masses can take over up to 12% of the heating energy.
Windproofness
Windproofness means that measures are taken to prevent wind from flowing through a component. This is intended to prevent the component from cooling down and at the same time also prevent the entry of pollutants into the component. Layers to create windproofing are i. d. Usually arranged on the outside (i.e. on the cold side exposed to the wind). In solid or masonry construction, the windproofness in the area is ensured by the external plaster, but penetrations (e.g. through the rafters) must be considered in planning and technical terms. Otherwise, uncontrolled joint formation or tears in the plaster can lead to so-called wind flows, which must be avoided.
Airtightness
This describes all measures that prevent an exchange of air between the indoor and outdoor climates, i.e. H. across the system boundary. The much-cited "air out of sockets" has nothing to do with windproofness; it is due to a failure of the LDS (= airtight system). Layers to create airtightness are i. d. Usually arranged on the inside (i.e. on the warm side of the insulation material).
The LDS usually consists of solid components that are airtight in themselves, such as concrete, internally plastered masonry, large-area building boards such as plasterboard or OSB panels, as well as foils or papers, which are glued to the solid components with suitable measures such as adhesive tapes or acrylic adhesive. The foils themselves must also be glued airtight at the longitudinal and transverse joints, as well as airtight sheet materials at the transitions and connections. All penetrations through the LDS must be made airtight, be it with prefabricated sleeves or with specially suitable adhesive tapes.
Inadequate airtightness represents a violation of the recognized rules of technology since DIN 4108 Part 7 on 8/31. July 1998 was published in the Federal Gazette. It does not have to be explicitly agreed in the contract for work, construction or in the sales contract, as it always represents an owed service.
Inadequate airtightness can cause considerable damage. B. a tear in a film only 1 mm wide and 1 m long per day (during the heating season ) causes condensation of around 360 grams. As a result, an insulation material can become completely soaked in winter, loses most of its insulating effect , and black fungus infestation can develop behind the ceiling cladding, which is only visible after the black fungus infestation has penetrated through the cladding.
The airtightness test is carried out using the so-called differential pressure method using the BLOWER-DOOR test. The measuring process is regulated in EN ISO 13829. The maximum permissible airtightness values are regulated in EnEV and DIN 4108. The permissible n50 value is the quotient of the amount of air conveyed (with a pressure difference of 50 Pascal) and the room volume. If z. B. 1500 m³ of air per hour are conveyed during the BLOWER DOOR test and the building has an air volume of 500 m², n50 1500/500 = 3.0. The EnEV specifies binding maximum values for certain building situations: Buildings without a ventilation system may have an n50 of 3.0; with ventilation system only from 1.5. The Passive House Institute prescribes a maximum air exchange rate of 0.6 for passive houses ; this value is not easy to achieve.
Humidity control
It regulates the protection against ingress of water. Moisture comes in two ways, inside and outside. From the inside through the release of water vapor (cooking, breathing, washing, etc.) and from the outside through rain, dew, etc. The moisture from the inside must be removed by ventilation; only a small part diffuses through the wall (usually well below 10 %). However, the surface has a buffer function up to a depth of about 1 cm. It stores moisture when the indoor humidity increases and releases it again when the humidity decreases. This means that there is more even humidity in the interior.
exposure
As a rule, interiors should be exposed to natural light . That is why windows are arranged in the outer walls or the outer walls are partially or entirely designed as glass facades . Translucent materials are used to achieve exposure without transparency . In the past , these were often glass blocks , but these usually do not meet today's requirements for thermal insulation.
Soundproofing
This type of insulation means soundproofing against external noise, e.g. B. Traffic noise and between rooms, DIN 4109. Most of the time, requirements are placed on the external sound insulation. Even if it is loud outside, the noise in the building should not be disturbing. The easiest way to achieve this is with a lot of mass, but sound-insulating materials such as glass wool can also help.
ventilation
Inside the building, moisture and CO 2 are released and oxygen is consumed. In order to restore indoor air quality and prevent mold, ventilation must be provided. In individual cases ventilation openings are made in the outer wall, in the majority of cases the windows are opened for ventilation, and because of their convenience, separate ventilation systems ( defined residential ventilation ) are becoming increasingly popular.
Fire resistance
External walls must have fire protection in the sense of preventive fire protection in accordance with DIN 4102 have. A house should not start to burn due to flying sparks and heat radiation , and if it burns inside and / or outside, the wall should retain its load-bearing function (at least for a certain time).
Construction methods
Single-shell outer wall without thermal insulation
The single-shell outer wall without thermal insulation consists of lightweight bricks such as lightweight concrete , aerated concrete or thermal insulation and vertically perforated bricks . The usual wall thickness is 36.5 cm (without plaster). 30.0 cm, 42.5 cm and 49 cm thick walls are also possible. Thermally insulating bricks have a very low bulk density (specific weight) due to their high percentage of holes (lightweight concrete and brick) or enclosed air pores (aerated concrete ). The lower the thermal conductivity of a wall, the better the thermal insulation. These stones, which are optimized on one side for thermal insulation, achieve thermal conductivities of 0.07 to 0.12 W / (m · K). For comparison: the thermal conductivity of wood is between 0.13 and 0.20 W / (m · K); Thermal insulation materials for exterior walls have thermal conductivities of 0.025 to 0.040 W / (m · K) (see DIN 4108). The low bulk density, which is positive for thermal insulation, has a negative effect on sound insulation and fire protection ( fire resistance ). It should also be noted that the low heat storage capacity of the stones has a negative effect on heat protection ( summer heat protection ).
Weather protection is guaranteed by an external plaster that is matched to the substrate.
Single-shell outer wall with thermal insulation
The single-shell outer wall with thermal insulation usually consists of a heavy, load-bearing wall panel and thermal insulation applied from the outside. The load-bearing wall panel is at least 11.5 cm thick. It consists of bricks with a high bulk density such as sand-lime brick , solid brick , concrete or reinforced concrete. The thermal insulation is carried out by a thermal insulation composite system (ETICS) according to general building authority approval, e.g. B. made of polystyrene foam or mineral fiber boards. Depending on the approval, the insulation panels are glued, dowelled, or glued and dowelled. The insulation material thickness can be selected so that every insulation standard can be achieved. The plaster provides weather protection . As an alternative to ETICS, thermal insulation with rear ventilation and curtain walls made of fiber cement, metal or wood are used.
Double-shell outer wall
The double-shell outer wall is essentially constructed like the single-shell outer wall with thermal insulation. Weather protection is provided by a 9 to 11.5 cm thick facing layer made of facing bricks, clinker , sand-lime brick or concrete stone facing . The facing shell is attached to the rear wall shell (supporting shell) with wire or dowel anchors. The shell distance (between inner and outer shell) is limited to a maximum of 15 cm according to DIN 1053. Through the use of generally approved wire and dowel anchors, shell spacings of up to 20 cm are possible. According to DIN 1053, double-shell walls are to be further differentiated in terms of their construction
- with core insulation (the shell space is completely filled with thermal insulation)
- with thermal insulation and at least 4 cm of air space
- with air layer (only to be found in existing buildings due to today's thermal insulation requirements)
Rear-ventilated curtain wall
See main article Curtain ventilated facade
The curtain-type, rear-ventilated facade is a multi-layer outer wall construction in which the outermost layer, which serves to protect against driving rain , is separated from the layers behind (insulation) by a layer of air .
Constructive division
External walls can assume static functions in the building if it is a load-bearing external wall. Non-load-bearing external walls and self-supporting external walls, on the other hand, have to transfer their loads and moments to the internal structure or only transfer their own loads and moments.
Load-bearing outer walls
Load-bearing outer walls serve to divert moments and forces, such as those
- from the roof with possibly additional snow load .
- from the loads of the ceilings borne by the outer wall.
- the wind loads
- the bracing of the building.
Non-load-bearing exterior walls
Non-load-bearing exterior walls are exterior walls that do not transfer any loads or moments. This includes parapets and infills in particular. Curtain walls, usually referred to as curtain walls , facing shells and thermal insulation composite systems must transfer the loads acting on them (dead weight, wind loads and moments) to the supporting structure of the building via connections, usually a skeleton structure (see skeleton construction ). These facades are primarily used for weather protection and shield the interior from rain , drafts and excessive solar radiation . When using thermally optimized substructures, additional insulation materials can also be used. This construction method of an outer wall was developed in particular in order to functionally separate the supporting structure and room closure so consistently that they can be designed in an optimized way with their specific requirements. After pioneering projects (manufacturing building of Margarete Steiff GmbH in Giengen an der Brenz, 1903–1910), the origins of this technology have been noticed especially since Walter Gropius , who developed a millennia-old building principle of solid construction, namely that the building corners, the proverbial corner stones, guarantee stability , dissolved in glass.
So-called self-supporting outer walls (e.g. facing shells) also divert their forces vertically over several floors into the ground via their own construction and are connected to the supporting structure of the building for the transmission of wind forces.
