Insulation of timber frame extension

[Cliffside1]

Please please advise. Our architect has listed 150ml insulation to go into our timber frame extension. This means the space is reduced. I spoke with building regs who say it does not matter what size as lobg as it is a U value of 0.21. We have spoken with celotex who unbelievably could not tell us which product was needed. Naturally we would prefer the cheapest and narrowest option. Can anyone help.

 

[JP_]

well, when I had a loft conversion, pretty sure it was 75mm overlaid with 25mm.
Building regs for my extension requires 100mm rockwall, which is about equivalent of 50mm board, I think. But then, there is 2 concrete blocks, one of which is an insulating one.

150mm is probably more than needed - if space is an issues, put more in loft and floor, and the least you can get away with in the walls.

 

[freddiemercurystwin]

Use the free Celotex calculator online, Celotex can't tell you over the phone as there are other factors involved.

In anycase whoever you spoke to at Building Control was wrong, the U Value required for a new domestic extension wall is 0.28 not 0.21 (which is worse ie needs less insulation).

The last timber frame extension I drew up had 80mm Celotex between the studs and that achieved 0.28.

 

[Footsoldier888]

I think in England you generally have to have a 140mm frame to meet these U values, so you may be stuck with that sort of dimension anyway.

 

[JP_]

Yeah, I think I was quoted 80mm board for my external insulation, to get the solid walls up to current standards.
Don't forget, the cladding / render will have some insulation too, as will any boarding put on the walls....

 

[freddiemercurystwin]

I think in England you generally have to have a 140mm frame to meet these U values, so you may be stuck with that sort of dimension anyway.

Eh?

 

[^woody^]

Tell your "architect" to redesign it. You are paying him to design to your needs.

 

[^woody^]

The last timber frame extension I drew up had 80mm Celotex between the studs and that achieved 0.28.

But that does not allow for the studs (thermal bridge) nor the services (reduced insulation).

 

[Footsoldier888]

Eh?

Sorry if thats wrong!

What I should have said is that newbuilds are mostly 140mm frames now because of insulation requirements.

 

[freddiemercurystwin]

It allowed for 140mm studs, insulation only between the studs so a 65mm void for services as in fact I could have got away with 75mm.

 

[^woody^]

It allowed for 140mm studs, insulation only between the studs so a 65mm void for services as in fact I could have got away with 75mm.

View attachment 141282

Oh. I was thinking in context of the OP in that 140mm was too thick a wall, and I imagined that you meant you designed a slimmer frame with 80mm insulation full fill.

 

[motorbiking]

Another option might be to look at a thin joint system if you need slimmer walls. It depends on the final finish needed.