Single skin garage conversion

Your plan sounds great. Ensure you leave a 50mm gap between the back of the kingpsan and the brick wall, otherwise you’ll get damp and condensation build-up. Timber needs to be treated. If you are able to, it’s a good opportunity to also fit a brush-on damp barrier or tanking slurry.

Hi, Your general approach is sound, but with a 20-year-old single-skin garage there are a couple of details that will make the difference between a warm, dry office and one that suffers from condensation issues a few years down the line. Personally, I would avoid fixing the stud wall directly against the brickwork. Instead, leave a small cavity between the existing wall and the new timber or metal studwork. This helps prevent moisture bridging and allows the wall to breathe. Between the studs I would typically install rigid PIR insulation such as Celotex or Kingspan, then add a continuous insulated plasterboard layer internally before plastering. The fact that you can see the damp proof membrane protruding from the slab is a good sign, as it suggests the original floor was constructed correctly. For the floor, I would normally install a suitable damp-proof membrane if required, followed by rigid insulation and either a floating chipboard floor or a screeded finish, depending on your final floor covering and available floor height. One thing often overlooked on garage conversions is that damp problems are more commonly caused by condensation than by water penetration. Once the space becomes heated and occupied as an office, adequate insulation and ventilation become just as important as damp proofing. Trickle vents, background ventilation and careful detailing around windows and doors all play a part. I'd also be looking at the existing floor level, ceiling construction, roof insulation, and whether the external brickwork is showing any signs of moisture penetration before recommending a final build-up. From what you've described, I don't see any immediate reason why the conversion couldn't be completed successfully, but I would want to inspect the garage before confirming the exact wall and floor specification. Happy to discuss further if you'd like some guidance on the best insulation build-up and how to achieve Building Regulations compliance for an office conversion