Timber frame wall query. Multifoil or PIR detail.

[tonyheat]

I am looking to build a timber frame wall with insulation up to current standards (lean to shed). The problem I have is that I need to build close to the boundary, and so have difficulty in accessing the one wall from the outside. The wall s about 2.5m long, I therefore need to make in sections (which causes problems with water ingress in the joints, or able to prefabricate and move unit into place one the cladding is fitted)

I was looking at using 6x2 studwork, with 100mm PIR insulation, but this will increase the thickness and weight of the unit. The wall is not load bearing, so could this be reduced to 4x2 or even 3x2, but will probably need to consider a mutifoil rather than PIR?

Does Multifoil offer similar insulation benefits to PIR. Ecohome (http://www.ecohome-insulation.com/files/ww/EcoQuilt%20Data%20Sheet%20Walls.pdf) looks similar to YBS Superquilt, and is fitted across the inside of the studwork, a extra 25mm batterns and then plaster boarded. The vapour barrier should not be needed. Would a single layer of Ecohome (2.272 m²·K/W 6 Layer), offer a similar insulation factor to 100mm PIR, (or Superquilt 2.71 m²·K/W)


Upvc weatherboarding
Batten 25mm
Breather Membrane
OSB Board 18mm
Studwork
Vapour Membrane
Plasterboard

 

[jeds]

You won't achieve anywhere near the same thermal value with multifoil alone as the same thickness of PIR. And multifoil is basically useless unless fitted correctly - and that means the foil must be battened and suspended with clear cavities either side. So by the time you've messed around with all that malarkey you'll have a thicker wall and it will be a lot more hassle. I would suggest 100mm stud with 75mm PIR. Use a breather membrane on the outside (beneath the weather layer) and a vapour barrier inside before the boarding.