Installation practice for renovating windows

Inexpensive windows can be produced with U_w values between 0.75 and 0.95 W/m²K. The triple glazing incorporated generally has U values of 0.5 to 0.7 W/m²K combined with a composite edge seal of high thermal quality; and then insulated frames with U values of 0.65 to 0.8 W/m²K are needed.

For high-efficiency renovation not only the quality of the actual windows is important, but also how they are installed!

In order to preserve the original appearance and avoid thermal bridges, the windows should be shifted outwards by the thickness of the wall insulation. Together with an increased frame depth of 10 to 12 cm, this makes it possible to minimize thermal bridging – the insulation should enclose the frame as far as possible. In addition airtight masking is necessary, joining window and airtight level directly; this can be implemented against the indoor plasterwork. In principle an airtight level is feasible, too, for instance in the ETICS adhesive layer.

Masking around the windows to tie in with the airtight level in the ETICS adhesive layer. Insulation is laid around the frame in order to minimize thermal bridging (source: Schulze Darup)

As a general rule renovating the windows should always be planned in conjunction with renovating the external walls, so as to avoid physical problems. If new airtight windows are installed but the external walls are not insulated, humid indoor air can condense on the cold walls and lead to mould developing.