From the worst room to the warmest
This small rear extension used to contain the coldest and dampest room in the house. Insulating the roof, outside walls and floor, together with better moisture extraction, transformed it into the room the homeowner now describes as the warmest and least damp.
What changed
The rear bathroom extension was single-skin and uninsulated when the homeowner moved in, in 2011, and they remember it as the coldest and dampest room in the house. A couple of years later they added about 25 mm of internal wall insulation and insulated the roof, which made the room slightly better but did not transform it. The main retrofit came in 2024: the roof was rebuilt as a warm roof, external wall insulation and render were added, and a new insulated floating floor raised the previously low floor closer to the level of the rest of the house. A new extractor fan was also installed to remove moisture, and the bathroom was refitted with a shower, toilet and basin in place of the old bath.
Why it matters
Addressing the roof, walls, floor and ventilation together, not just refitting the bathroom fittings, is what changed how the room feels day to day. The homeowner reports that the room that used to be the coldest and dampest in the house is now the warmest and least damp, and credits the extractor fan especially for the improvement in moisture. That outcome is the homeowner's own lived experience of the room, not a recorded measurement.
The 2024 build-up
The old roof was removed and replaced with a warm-roof build-up using 150 mm of Celotex-type insulation. 100 mm of external wall insulation was added and rendered. The floor received 100 mm of Celotex-type insulation under a waterproof tongue-and-groove chipboard floating floor. A new extractor fan was fitted, and the window was moved for privacy from a neighbouring office.
Benefits
- A previously cold, damp room now feels warm and comfortable, in the homeowner's own experience.
- Better moisture extraction, alongside the insulation, is credited with much of the improvement.
Limitations
- This is one homeowner's experience, not a universal specification or a measured result.
- There are no recorded before-and-after temperatures, humidity readings, U-values or energy savings for this room.
- An appropriate approach for another property would depend on its own construction and moisture conditions.