Preserve windows instead of replacing them
Windows shape the character of a house and are contemporary witnesses. However, older windows often no longer meet today's energy requirements. When the original windows are replaced, the authentic expression of a building is often lost. However, there are solutions to preserve the windows.
The preservation of historical monuments in Basel-Stadt observes with concern that historically valuable windows are creeping away. Carefully crafted windows are sometimes even replaced by plastic windows; characteristic muntins are simply left out. As a result, the appearance suffers - both from the outside and the inside. "The houses are literally having their eyes gouged out," reads a summary in the 2015 annual report of the cantonal monument preservation office of Basel-Stadt. The central question: Can the preservation of historically valuable building fabric be combined with energy efficiency and living comfort? The answer is "yes." There are various ways to upgrade windows. For this reason, the preservation authority recommends that modernization of the windows be examined in every case before the contemporary witnesses are thoughtlessly replaced. If replacement is unavoidable, the new windows should have a high-quality design and be well integrated into the building.
Meticulous craftsmanship
The window as a component must meet many technical requirements: It connects the inside with the outside and provides natural lighting. It serves for controlled air exchange, security, sound and heat insulation.
The original substance, layout, proportion and construction make the windows contemporary witnesses that shape the feeling of space in a building. Because often historical, but also modern windows, have a unique charm, which is often lost in a replacement. That it can be done differently is shown by the window construction company Quadra Ligna from Basel, which has developed a renovation system for windows. "Our process has been constantly developed and improved over more than 40 years," says managing director Stephan Hasler. The outside of the windows is doubled up with a custom-made profile made of weather-resistant Swiss oak and then glazed or painted. "Even warped or crooked frames are no obstacles, as the doubling is customized for each window," Hasler explains. The glass is replaced with double or triple insulating glazing designed for optimal thermal insulation and, if necessary, special soundproofing and safety requirements. If special renovation glass is used, the distinctive surface of the original glazing is also retained. Thanks to a circumferential seal on the weather side, the window is wind and driving rain proof. The joint between the new doubling frame and the historic component provides downward ventilation so that any moisture can escape.
Save energy and improve the feeling of living
This method achieves a compromise: the historic building fabric is preserved and today's requirements are met. Hasler explains: "Energy consumption is reduced and comfort is increased because drafts no longer enter the building and radiation asymmetries, i.e. temperature differences between windows and interior walls, are minimized. The energy-saving potential is considerable: If an old simple window glass has a heat transfer coefficient (Ug) of around 5 W/(m²K) before renovation, this is around 1 W/(m²K) after renovation thanks to the second layer of glass and special coatings.
If renovated instead of replaced, the proportion of glass is greater with the same glass structure, because modern frames are usually wider than the originals. The connection details inside are preserved, which is of interior architectural relevance, especially in the case of artistically designed reveals. Front windows - especially retrofitted ones - which distort the architectural image, are not very user-friendly and reduce the incidence of light, become superfluous.
Quality pays off
The buildings of architect Ernst Zimmer and his brothers show that it pays to renovate windows. After taking over their parents' house in Basel's Gundeli district in the 1970s, they gently renovated it. In order to preserve the fabric of the building, he decided against replacing the windows on the front and had them doubled up by Quadra Ligna's predecessor company as early as 1987. When the windows on the rear building were getting on in years, it was clear to him, "Since the windows on the front building are still perfect more than 30 years after the renovation, we wanted to renovate this way again."
Even if the procedure seems costly - considering that some neighbors have renewed the windows twice in the same period, this type of renovation also saves money in the long term.
