Insulation for Your Extension

Insulation is the part of your extension that nobody sees and everybody pays for if it's wrong. Get it right and your new room stays warm with minimal heating. Get it wrong and you'll feel a cold spot on the wall for the next 30 years, wondering why one corner of the kitchen is always five degrees cooler than the rest.

The real risk isn't choosing the wrong product. PIR, mineral wool, EPS: they all work. The risk is poor installation. A 10mm gap behind a PIR board can halve the thermal performance of that entire wall. Cheap vapour barriers sweat, stain your ceilings, and rot your timbers. Rushed floor insulation the day before screeding creates an uneven base that's buried under concrete for the life of the building.

And building control will inspect it. If your insulation doesn't match the approved specification, or if the vapour control layer has gaps, the BCO can reject the work. That means stripping off plasterboard you've already paid to have fitted. Budget for at least one specification upgrade mid-build. It happens more often than it should.