Window renovation

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Window inventory in a monument. Left: window renovation that is not listed as a monument. (Replacement of the historical window stock with single-leaf, tightly closing “one-hand turn-tilt windows”). Right: historical window stock. (Two wings with skylights.)

The term window renovation is generally used today when it comes to the replacement, modernization or carpenter-like overhaul of windows or window stocks that no longer meet today's demands and standards in terms of heat or sound insulation and comfort. When renovating a window, the airtightness should be improved and the heat transfer coefficient (energy loss) or sound transmission reduced.

The renovation measures can extend to all components of the window (i.e. glass, frame and structural connection). They serve to adapt the structural substance to modern requirements through technical and functional changes. These measures represent irreversible interventions in the building fabric and are not compatible with the monument law of the federal states. Windows that are under monument protection must be preserved in accordance with the principles and standards of window repairs . The window renovation is to be distinguished from the window repair. Renovations in existing buildings are usually subject to active inventory protection . The renovation measures must be preceded by an inventory .

Definition of terms

Irreversible interventions in the historical building substance, which serve the energetic renovation , the functional improvement or a modern usage requirement, are now commonly referred to as window renovation . Before the year 2000, the term redevelopment was still used in the specialist literature on monument preservation . Today this term is hardly used in the context of monument preservation. It has been replaced by the term window repair and its most common practical implementation, window restoration. As a result of this shift in meaning , most of the measures that are now referred to as window renovation are no longer compatible with the preservation of monuments and with the principles of monument protection in accordance with the Venice Charter and the German National Committee for Monument Protection , as well as with the monument protection laws of the federal states. Window repairs are used today in connection with monument protection and monument preservation as the general umbrella term for a number of measures for preservation . For buildings or facades that are under monument protection, only window repair is possible according to the principles and monument protection laws mentioned.

Window renovation in the old building

→ For more information on interfering with the physical properties of historic windows, see the main article, window repairs

Pattern for window renovation on an industrial scale.
Window renovation in an old building that is not listed as a monument.

In order to meet the high thermal insulation requirements, as stipulated in Germany for example by the Energy Saving Ordinance (EnEV), new windows must have a high level of airtightness, which in turn is ensured by suitable seals. The thermal conductivity of existing windows can be reduced by various measures. This goal can e.g. B. can be achieved by special thermal insulation coatings on the window panes (for example tin oxide , silver or gold ) and a gas filling in the space between the panes. To improve the sound insulation, the window panes can be made particularly heavy. The pane structure can also be designed asymmetrically and the space between the panes can optionally be filled with a heavy gas (previously, for example, sulfur hexafluoride ).

Installation of new windows in the old building

The replacement of older windows (single windows with normal glass and box windows) by modern windows with lower U-values not only affects the thermal insulation, but also has a significant influence on the moisture balance of old buildings and apartments. Since single windows regulate the moisture content of rooms as so-called "target condensers" by draining condensation water, excess moisture in the room air condenses on the outside walls after a window has been replaced. The resulting mold infestation only becomes visible after several months and is a major problem in the renovation of old buildings . Therefore, the rule applies that the U-value of windows must not be lower than that of the outer walls. In order to comply with this rule, when replacing historical windows, it is pointed out that the facade must also be insulated. The KfW promotes through various programs this kind of window renovation. The Zentralverband des Deutschen Handwerks (Central Association of German Crafts) points out the problem of interfering with the physical conditions of historical buildings: “ If historical buildings are upgraded airtight in accordance with the requirements of the EnEV, e.g. B. through the installation of modern double glazed windows and inner cladding in front of the outer walls, it can lead to critical relative room humidity of over 50 percent in the cold winter months. In the case of external component surfaces with low thermal resistance, i.e. poor thermal insulation properties, mold infestation is the consequence of this supposed energy-saving measure. (...) The dilemma of the Energy Saving Ordinance with regard to architectural monuments and building fabric worth preserving is that it confronts old buildings with the philosophy of contemporary, environmentally friendly new buildings. For the monument, however, the unrestricted application of modern insulation strategies means risks and damage up to and including the total loss of individual components. "( Central Association of German Crafts : Much Potential for Conflict: Preservation of Monuments against Climate Protection. )

Replacement of historical panes with insulating glass panes

Insulating panes that have become blind in "renovated" historical windows.
Pattern for replacing historical panes with insulating glass panes in historical windows.

By replacing single glazing with multi-pane insulating glass in historical windows, energy savings should be achieved without changing the external and internal appearance of a building. The energetic benefit of this irreversible intervention in the substance of historical windows is controversial. The measure also contradicts the principles of the Venice Charter and the monument preservation principles for window maintenance , as formulated by the Association of State Preservationists in the Federal Republic of Germany in 1991.

Insulating glass has a limited lifespan. According to DIN 18545-1 (sealing of glazing with sealants; requirements for glass rebates), leakage of the seal between the individual panes is permissible. Various factors, such as UV radiation , condensation , mechanical and thermal stresses, but also chemical reactions between the window putty and the edge seal of the insulating glass panes can make them blind. Damage of this kind was the reason that insulating glazing was viewed with skepticism by the monument protection authorities. The glass industry has reacted to the deficiencies and developed special procedures to prevent condensation from forming on the edge seal.

Equipping historical windows with insulating glass panes is in most cases contrary to the reversibility of interventions in the historical substance in accordance with the principles of monument preservation. In Germany, insulating glass panes are generally guaranteed for 5 years (as of 2011). To install the panes, the glass rebate generally has to be milled deeper, as insulating glass panes are at least 10 mm thick. This intervention is irreversible in terms of monument protection and also weakens the load-bearing capacity of the window sash.

Insulating glass panes are usually produced by gluing two individual panes at least 4 mm thick with a gas-filled gap that is more than 10 mm wide. As a special version for installation in historical window frames, insulating glass with 3 mm thick panes and a gap of only 4 mm is available, resulting in a total width of 10 mm. However, the narrow gap increases the shear stress on the edge seal due to the thermal expansion of the glasses if one of the panes is heated more than the other, for example through solar radiation on the south side of the house.

Insulating glass panes with the smallest possible pane thickness of 3 mm have at least twice the weight of the historical panes (3 mm thick glass weighs around 7.5 kg / m², double-pane insulating glass weighs at least around 15.5 kg / m², with a soundproofing effect at least around 18 kg / m²). The historical material and construction of historical windows is not designed for such a weight and such interference. To stabilize the weakened frame, the originally unglued corner connections of the casement frames are often glued, which makes future repairs to the window frame more difficult. Since the original repairability of historical windows is no longer given after such an intervention, this refurbishment method is not in accordance with the principle of preservation of the substance and reversibility and is not suitable for window stocks that are listed.

Window renovation and energy saving ordinance

According to the Energy Saving Ordinance, an exception regulation according to § 24 EnEV (exceptions) can be used not only for monuments, but also for “building fabric that is particularly worthy of preservation” : or affect the appearance or other measures lead to a disproportionate effort, the requirements of this ordinance can be deviated from. " According to § 25 EnEV (exemptions), exemptions from the EnEV are possible in the renovation of old buildings due to the inefficiency of the measures: " (1) the appropriate regional authorities at the request to free themselves from the requirements of this Regulation where the requirements in individual cases due to special circumstances by an unreasonable effort or in any other way to undue hardship lead. There is undue hardship in particular if the necessary expenses within the usual life in requirements for existing buildings within a reasonable time by the resulting savings can not be achieved. " § 5 Energy Saving Act (EnEG) contains the legal basis for exemption under § 25 EnEV .

See also

Individual evidence

  1. ↑ a b c d Tobias Huckfeldt, Hans-Joachim Wenk: wooden windows - construction, damage, renovation, maintenance. Cologne 2009, ISBN 978-3-481-02504-5 , p. 260.
  2. ↑ Michael Stahr, Jürgen Weber, Hilmar Kolbmüller, Friedhelm Hensen, Uwe Wild: Building renovation: Recognizing and remedying building damage , Wiesbaden 2011, ISBN 978-3-8348-1406-7 . P. 4
  3. ↑ Jörg Böhning, Heinz Schmitz: Modernization of old buildings in detail. Verlagsgesellschaft Müller, 2005, ISBN 3-481-02228-X .
  4. ↑ a b c d Wolf Schmidt: Repair of historical wooden windows. In: Monument preservation information. Bavarian State Office for Monument Preservation, Munich 2004, ISSN  1617-3147 , p. 21.
  5. ↑ Ernst Neufert: Building design theory. Braunschweig / Wiesbaden 1996, ISBN 3-528-68651-0 , p. 272.
  6. ^ A b c d Manfred Gerner, Dieter Gärtner: Historical windows. Development, technology, monument preservation. Deutsche Verlags-Anstalt, Stuttgart 1996, ISBN 3-421-03104-5 .
  7. ↑ Michael Petzet: Principles of the preservation of monuments. Monument preservation information. Bavarian State Office for Monument Preservation. Munich 1987.
  8. ↑ a b c d Association of State Monument Preservators in the Federal Republic of Germany. Worksheet 8, Instructions for the treatment of historical windows in architectural monuments. Wiesbaden 1991.
  9. ↑ Frey, August, Günter: Structural engineering, specialist knowledge of construction. 10th edition. Europa Lehrmittelverlag, 2003, ISBN 3-8085-4460-0 .
  10. ↑ Moisture damage and mold. ( Memento of the original from March 6, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. on: khries.de  @1@ 2Template: Webachiv / IABot / www.khries.de
  11. ^ Claus Arendt among others: Window renovation. Building Technology Working Group of the Association of Monument Preservers, Munich 1984, p. 17.
  12. ^ Martim Saar: Ventilation in old buildings. Worksheets of the Bavarian State Office for Monument Preservation, Munich 2002, p. 2.
  13. ↑ https://www.kfw.de/media/download_center/foerderprogramme__inlandsfoerderung_/pdf_dokumente_2/59594.pdf  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / www.kfw.de  
  14. ↑ Much potential for conflict: Preservation of monuments against climate protection. on: zdh.de , November 19, 2010.
  15. ↑ DIN 18545-1 (sealing of glazing with sealants; requirements for glass rebates)
  16. ↑ http://www.fensterhandel.de/fenstersanierung/ Fenstersanierung
  17. ↑ Opinion on the Energy Saving Ordinance (EnEV) and the energy pass. (PDF; 72 kB) Information from the Association of State Monument Preservators, developed in autumn 2005 by the building technology working group

literature

  • Jörg Böhning, Heinz Schmitz: Modernization of old buildings in detail. Verlagsgesellschaft Müller, 2005, ISBN 3-481-02228-X .
  • Tobias Huckfeldt, Hans-Joachim Wenk: Wooden windows - construction, damage, renovation, maintenance. Cologne 2009, ISBN 978-3-481-02504-5 .
  • Wolf Schmidt: Repairing historical wooden windows. In: Monument preservation information. Bavarian State Office for Monument Preservation, Munich 2004, ISSN  1617-3147 .
  • Michael Petzet: Principles of Monument Preservation. In: Monument preservation information. Bavarian State Office for Monument Preservation. Munich 1987.
  • Hans-Rudolf Neumann: Windows in the existing building: Basics of renovation in theory and practice. Expert-Verlag, Renningen 2003.
  • August Günter Frey: Structural engineering specialist knowledge of construction. 10th edition. Europa Lehrmittelverlag, 2003, ISBN 3-8085-4460-0 .
  • F. Schleicher: Pocket book for civil engineers. Vol. 1, Berlin / Göttingen / Heidelberg 1955.
  • K. Gösele, B. Lakatos: Sound insulation of windows and glazing. In: Deutsches Architektenblatt. 1979.
  • Manfred Gerner, Dieter Gärtner: Historical Windows. Development, technology, monument preservation. Deutsche Verlags-Anstalt, Stuttgart 1996, ISBN 3-421-03104-5 .
  • Association of State Monument Preservators in the Federal Republic of Germany. Worksheet 8, Instructions for the treatment of historical windows in architectural monuments. Wiesbaden 1991.
  • Otfried Rau, Ute Braun: The old building. Renovate, restore, modernize. Leinfelden-Echterdingen 1991, ISBN 3-87422-613-1 .
  • Ernst Neufert: building design theory. Braunschweig / Wiesbaden 1996, ISBN 3-528-68651-0 .

Web links