What this work covers
Wall insulation starts by drying and cleaning the cold wall, then builds a continuous layer through reflective insulation, XPS board, frame infill, and a sealed vapor barrier. The critical details are around windows, inside corners, sockets, and penetrations, where a small break can concentrate condensation behind the finish.
When this work is needed
Review it when condensation, mold, or a cold surface repeatedly appears on an exterior wall, an expanded balcony wall, a lower window frame, or an inside corner. If the wall is wet from leakage, repair and dry it first; sealing insulation over active moisture can hide the stain while mold continues behind it.
Decide before the wall is built out
Set the thermal and vapor-control layers before fixing the final wall depth.
- Exact exterior-wall, expansion, window, and corner areas to insulate
- Insulation products and thicknesses, including infill within the framing
- Location of the vapor barrier and the method for sealing laps and staple holes
- Thermal-bridge treatment at frames, corners, sockets, and pipe penetrations
- Conflicts between the thicker wall and trim, doors, sockets, or fitted furniture
Check in the quote
The quote should describe moisture preparation and weak points, not just square metres of board.
- Are the insulation area, product, and thickness listed for each wall?
- Are mold removal, loose-finish removal, and full drying included?
- Are window frames, inside corners, and penetrations included in the foam-sealing scope?
- Are frame infill, vapor barrier, laps, and puncture sealing included?
- Is there a pre-closure check for lifting and outside-air entry with photographs?
If you have condensation photographs or an insulation quote, I can help identify weak edges and missing preparation.
What to check on site
Insulation should not become a new cover over the old damp wall. Dry the base, find the cold bridges, and keep both insulation and vapor control unbroken before closing it in.
- Existing Surface Cleanup and Vapor Prep Complete
Remove mold and weak finishes, let the wall dry, and distinguish leakage from surface condensation. Mark cold points and air gaps around frames, wall-to-ceiling corners, and penetrations so the repair has a defined boundary. - First Insulation Layer Complete
Fit the reflective layer flat and tape its joints continuously into the window and floor edges. Reseal every cut made around sockets or services instead of hiding a patch beneath the next layer. - XPS Board and Wood Frame Complete
Cut XPS board closely between the battens and fill the frame without compressing mineral wool or leaving voids. Refix any board that rocks, sags, or projects beyond the framing before plasterboard is installed. - Vapor Barrier, Inspection, and Cleanup Complete
Lap the final vapor barrier, seal staple holes and service openings, and check the whole surface by hand. Use thermal imaging where available to find a remaining break below windows or at corners, then record the closed work before the next trade arrives.
Where problems usually start
- Open insulation joint An unsealed joint becomes a narrow thermal bridge where condensation can trace the board line.
- Insulation over a damp wall Moisture trapped behind a loose board can support mold even after the room-side stain disappears.
- Missing lower-window treatment A small unfilled edge below the frame can remain the coldest surface and collect winter condensation.
- Torn or punctured vapor barrier Open laps and staple holes allow indoor moisture into the insulation and gradually reduce its performance.
Cleaning mold and covering the wall is not a complete repair. Confirm the moisture source, drying, thermal bridges, air leakage, and vapor-barrier continuity together.
Before closure, keep the base-moisture result, product and thickness, frame infill, window and penetration details, vapor-barrier photographs, and the final lifting and air-leak check.
Timing and records
Allow about 16 to 24 hours on site. Mold treatment, wall drying, insulation area, and framing details may require additional waiting time.
Keep the product and thickness by wall, drying result, window and penetration treatment, frame infill, full vapor-barrier photographs, and the final thermal or air-leak inspection.
The insulation is concealed between demolition and plasterboard, so checking both handoffs protects the evidence you will need later.