For buyers and owners of old buildings, much has changed with the introduction of the Energy Saving Ordinance (EnEV), LEGACY said. If they renew at least one-fifth of a facade front, they have to insulate it at great expense. What is less well known, however, is that the same rule applies to the renovation of windows.
If at least 20 percent of the windows on one side of the house, or even just their glazing, are replaced, then the new elements must insulate as well as a modern double-glazed insulating window.
It is not always sensible to replace windows in old buildings. For several reasons, box double windows, i.e. constructions with inner and outer sashes, should be retained as far as possible. Once refurbished, these have several advantages over simple “insulating glass windows”.
First, there is the appearance of the facade: old windows are often structured by sash bars, profiled frames and a central post so that the facade does not appear as lifeless and interchangeable as in houses with modern windows and large glass surfaces.
Also, there is the higher sound insulation. Even without new insulating glazing, double box windows insulate better against external noise than new one-piece windows. The prerequisite for this is that the joint between the sash and the outer frame is not too wide.
Even thermal insulation is almost competitive with insulating glass windows from the 1980s and early 1990s, thanks to the approximately 10 to 15 centimeter thick standing air layer in the space between the inner and outer sashes. Also – provided that the wood substance is intact – a significant improvement in thermal insulation and sound insulation can be achieved through subsequent measures.
This requires the installation of a modern, approximately ten to 15 millimeter thick insulating glazing and the additional provision of the window frame with a circumferential lip seal.
However, both measures should only be carried out on the inner sash. This is because the cold outside air must continue to flow through the space between the panes of box windows to prevent condensation from forming.
It has also been proven that the sound insulation of windows is optimal when the inner pane is heavier, i.e. thicker, than the outer pane.
For this reason, the reworking of the outer wings should – in addition to a professional new coat of paint – also include the replacement of damaged weather legs. This is the lower, slightly rounded end profile of the sash. The often damaged putty joints should also be renewed. The window often has to be made “lockable and lockable”, e.g. the locks have to be replaced or the rods have to be oiled.
Of course, the replacement of windows can also be unavoidable: If the old substance is too bad or if the single glazed elements have too thin frames for insulating glass panes.
New windows most often consist of plastic and wood. The advantage of plastic windows is that they are largely maintenance-free. Wooden windows, on the other hand, must be repainted at intervals of several years.
But these have usually slimmer frame profiles, and the portion of the glass surface is also higher: The areas are lighter thereby, which can be important with older houses with much smaller window openings.
When installing new windows, the joints between the window frame and the brickwork should be 15 to 25 millimeters wide and the space between them carefully stuffed with mineral wool. If only assembly foam is used instead, then there is the danger that this foam “shrinks” later and still tears gaps.
Heating heat then escapes there and it can become draughty in the room. Before the windows on the inside of the masonry are plastered again, the joint to the masonry should be sealed windproof. Here sealing tapes or plaster end profiles are usual.