Slab cavity insulation

[Ttw]

I'm looking at ordering 100mm insulation for a new build annex (100mm cavity) 

 

I've come across Knauf earthwool dritherm 32 and dritherm 37.

 

The 37 is quite a bit cheaper and wondering if anyone has any advice. I've been told that if using a full slab to go double the thickness of what kingspan would need to be. 

 

 

[tonyshouse]

I used 300mm of r32 May as well do the best you can while you are at it, making sure it all gets installed properly Makes a huge difference too.

[Ttw]

7 minutes ago, tonyshouse said:

I used 300mm of r32 May as well do the best you can while you are at it, making sure it all gets installed properly Makes a huge difference too.

300mm in the roof space? Surly not a cavity! I agree with doing the best so there's no regrets

[Miek]

300mm full fill cavity, gets you to passive standards. That is what I'm about to do also.

[Ttw]

1 hour ago, Miek said:

300mm full fill cavity, gets you to passive standards. That is what I'm about to do also.

Unfortunately I'm not able to build with such a large cavity, what type of building is the one you are talking about using a 300mm cavity? 

[tonyshouse]

My house http://tonyshouse.readinguk.org/

[wozza]

I used Dritherm 32 in 100mm cavity - if you shop around and buy in bulk you can get good deals.

 

"Gulp" I just did a quick google - the prices have shot up from last year.

Edited May 27, 2020 by wozza

[MikeGrahamT21]

Depends how much ££ you have to spend too, and what level of performance you are trying to achieve.

 

For my upcoming build which has a 100mm cavity, i'm using full fill Xtratherm CT/PIR boards, which are specifically designed to fully fill a 100mm cavity. Kingspan now also do a 90mm Kooltherm board, which gives about the same performance, but requires joints taping, and costs a lot more.

 

Both of these solutions will give around 0.16U using Celcon type blocks on the inner skin, which is almost passive house target for the walls (0.15U)

[Ttw]

3 hours ago, wozza said:

I used Dritherm 32 in 100mm cavity - if you shop around and buy in bulk you can get good deals.

 

"Gulp" I just did a quick google - the prices have shot up from last year.

I was pretty shocked too, fortunately I only need 50m2

[Ttw]

17 minutes ago, MikeGrahamT21 said:

Depends how much ££ you have to spend too, and what level of performance you are trying to achieve.

 

For my upcoming build which has a 100mm cavity, i'm using full fill Xtratherm CT/PIR boards, which are specifically designed to fully fill a 100mm cavity. Kingspan now also do a 90mm Kooltherm board, which gives about the same performance, but requires joints taping, and costs a lot more.

 

Both of these solutions will give around 0.16U using Celcon type blocks on the inner skin, which is almost passive house target for the walls (0.15U)

Definitely worth doing right the first time so there's no regr..... I've done that in previous extensions and regret not making it right the first time.