Windows account for 10 to 15 % of heat losses — but above all comfort: no more cold draughts and street noise. Two installation methods, three materials, two coefficients to read. Summary.
Full removal or retrofit? (diagram)
- Retrofit installation (over a sound existing frame): half a day per window, no wall repairs — but you lose glass area.
- Full removal: heavier (sill and reveal repairs), but maximum light and new sealing end to end. Prefer it if the old frame is tired or the project is already in the structural phase.
Reading a window label
| Coefficient | What it is | Target |
|---|---|---|
| Uw | Whole-window insulation (lower = better) | ≤ 1.3 W/m².K (subsidy threshold; ≤ 1.1 triple glazing) |
| Sw | Solar gain (higher = more free heat) | ≥ 0.3 facing south |
| Glazing | 4/16/4 argon standard; acoustic 10/14/4 street side | by exposure |
PVC, aluminium or wood
- PVC: unbeatable insulation/price, perfect in white — aesthetic limits on very large bays.
- Aluminium (thermally broken): slim lines, large sizes, colours — a notch below in insulation, a notch above in price.
- Wood or wood-alu: the charm and the duty of maintenance; often required in protected areas — check with the town hall and the building rules (external appearance = approval required).
Windows in = airtight home: the project can move on to insulation, boarding… down to the floors (the schedule).