Airtightness on stable conversion

[pstunt]

I am in discussion with my builder on how best to approach the challenge of airtightness for an old stable conversion. We are having to keep the original brick cavity walls and therefore need to insulate on the inside ( PIR )  and then plaster board and skim. This will have the benefit of hiding the wonky and uneven walls even though we will loose internal space.

 

My builder, by his own admission is not super experienced in achieving the level of airtightness I would like ( less than 3 ) but he is very willing. One suggestion he is thinking of is to simply stick a vapour barrier over the taped insulation prior to the plaster board and skim ? Obviously, there would be holes from the screws fixing the plasterboard but these would be plastered over.

 

Is this something that would work ? If so what sort of VCL would be suggested ?

[Jilly]

Maybe discuss it with your Building Control Officer? I've just done a stable conversion and airtightness was never mentioned (altho it is important, of course) and discuss what things you have to comply with and which bits are exempt for a conversion. For example, I was surprised to find I didn't have to comply with part M, but do double check. Don't go too airtight unless you are putting in MHRV, is my understanding. My builder hadn't had much experience of that and we didn't tape everything up

 

Also check which bits of the old building need to breathe.  Is external wall insulation an option? Can you not fill the cavity? I think my builder relied on foil backed insulation to act as a VCL, which some on here may tell me isn't good enough...

 

[pstunt]

Thanks, Jilly.

 

I should have said, I do intend to have MVHR, which is one of the driving factors of achieving below 3 airtightness. I am well aware I may not make my money back etc. but to me it's just as much about the other benefits such a system can provide. You are quite right, being a conversion means many of the building regs seem to be a lower standard required however I am keen to insulate as much as reasonably possible, partly to save on energy bills in the future. 

 

Whilst it's not impossible to fill the cavity, the general consensus is that there is a fair amount of risk that it in doing so may cause future problems. That is something I wish to avoid. Additionally, we couldn't have external insulation, as that would cover the building and would negate the arguable requirement that we couldn't knock down and rebuild the structure for historical reasons.

 

 

[MDC]

Perhaps 5mm of plastering all round is a good solution?