PIR insulation
Replacing windows before insulating the walls: how to avoid reworking the reveals
At a glance
If the windows are replaced this year but the walls will be insulated later, the window-to-wall junction has to work in two different conditions. First it must perform with the existing façade. Later it must accommodate the wall insulation, sill and finished reveal. Ask for a section showing both stages before ordering windows. It is then easier to agree what will remain, what is temporary and who will protect the joint between visits. Use this guide to prepare a discussion with the window installer and the façade contractor.
Start with the opening as it stands
Photograph the opening from outside and inside. Note whether the window faces a sheltered balcony or an exposed façade.
Record the depth of the reveal and the position of the existing frame relative to the masonry. In an older house, render thickness and reveal geometry can vary between floors. One measurement need not represent every window.
Draw both façade lines
Use one colour on the section for the existing wall face and another for the future render or cladding face. Include the full planned build-up. Board thickness alone does not locate the finished façade line.
If the installer proposes moving the frame from its existing position, ask how it will be supported and fixed. Insulation around the frame is not a substitute for the components that transfer the window loads.
Agree the frame-to-insulation junction
On the jamb detail, mark where the reveal insulation ends. Coordinate this with the window and façade systems. Do not set the frame overlap by copying the visible width on a neighbour’s window.
Check clearances around shutter guides, hinges and window drainage openings. A part that works with the bare wall may become inaccessible once the thicker façade is in place.
Plan the sill in both stages
On the external sill detail, mark its connection beneath the window and its outer edge in relation to the finished façade. If the first sill is temporary, agree how to remove it without damaging the permanent seal beneath the frame.
Show the sill ends as well as the middle section. Water drainage and the edge of the finish need resolving where the sill meets each jamb. Give the detail to both trades.
Who looks after the interim condition?
Identify sealing materials that will be exposed for a time. Check their permitted exposure and protection requirements in the instructions. Do not assume every joint can remain uncovered until the next building season.
List joint installation, temporary protection and inspection before façade work as separate responsibilities. If the second stage is delayed, it is clear who must check the protection and decide when it needs renewing.
Inspect one complete window junction
Use the first completed window as a sample for discussion. Inspect the head, both jambs and sill before the finishes cover them. Label photographs by room so they can be matched to the right detail.
After insulation is fitted, check that the window and shading still operate and that drainage remains clear. The inspection should establish that window, sill and façade work together; an even render finish is not enough to confirm this.
7 branches. Materials closer to your project.
- SEROCK — Dzierżenin 34 E
- BŁONIE — ul. Sochaczewska 138A
- RADOM — ul. Grobickiego 8
- ŁÓDŹ — Natolin 8
- OLSZTYN — Barczewo, ul. Prosta 9
- WROCŁAW — ul. Jerzmanowska 10C
- GORZÓW WLKP. — ul. Zielona 33/34
