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7 Aug 2019
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I've got a double garage at the rear of my property and I'm looking to attach a new "Shed" to the back of it. I've already laid a 4x3m 9 inch concrete slab with DPM but I'm undecided on how to proceed.

My choices have boiled down to the following and I'm keen to hear people's opinions.

1. Timber Frame with PIR insulation in the floor, walls and roof. Wrapped with a breather membrane then Feather Edge cladding externally. I'm unsure whether securing a timber soleplate directly to a concrete slab is advisable. Could I just wrap the DPM up over the slab and then DPC before securing the soleplate ?

2. Half brick dwarf wall of 4 of 5 courses of matching brick , then DPC on the brick and then secure the soleplate to the brick ? I'm worried that that those 4 or five courses of half brick wall would be cold and or damp ? Can I mitigate that ?

3.Build the entire structure from Thermalite block, wrap externally with breather and then secure featheredge externally. Frame internally for plasterboard finish. Not sure if wrapping Thermalite with a breather is enough ? How would Thermalite compare to approx 80mm PIR in a timber build for insulation ? I know it offers better sound proofing.
I'd definitely go with a couple of courses of brickwork, or better still those heffin' girt trench blocks. Then go timber frame and just fly your battens down to cover the masonry work with your cladding.

DPC under trench block and under soleplate.

DPM over concrete and lapped up trenchblock under DPC under sole plate

Celotex type insulation over DPM. The either screed or sheet flooring.

I'm sure Mike will be along soon to give you the definitive answer, since I've probably got the DPC/DPM details wrong. (its been a while)

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