Hi all,

I’m currently researching the effectiveness of external wall insulation being applied to a BISF property and I am in need of the dimensions of the building fabric.

This would mean the thickness of each layer of the external wall, plasterboard, quilt, columns, cladding etc.

Any chance this information is available anywhere?

Many thanks, Sam.

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Hi Sam and welcome. This is interesting, but may be rather tricky given that most of the layers are not continuous.

Downstairs the build up is from outside to inside:-

Concrete render on expanded steel laths – approx 50mm
C-sectional steel vertical stanchions of approx 70x60mm at approx 1.5m spacings.
Air gap of approx 75mm
Fibreglass insulation enclosed in brown paper, was probably about 30-50mm thick originally but may have sagged, it’s also nailed to the back of the internal wall lining so won’t be a continuous thickness as its compressed where nailed.
Timber studwork approx 50mm thick – obviously not continuous.
Plasterboard approx 9mm

Upstairs the build up is similar, except the outer layer is pressed steel a mm or two thick and the inner lining is typically hardboard rather than plasterboard.

The big issue I’ve never seen addressed is that the cavity in the wall is very well ventilated as it is open at the top to the loft and the steel cladding upstairs is far from airtight. It is also open to the void between the first floor and ceiling. Therefore any external insulation is likely to be bypassed by cold draughts in winter. Anywhere where there is a gap in the wall linings such as electrical sockets, below skirting boards, where holes have been drilled etc, or between gaps in the floorboards it is very easy to feel cold draughts in colder weather.


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