Frame is up (140mm stud, OSB sheathing, 25mm batten + Cement board cladding).

Insulation wise I was going for Knauff frametherm 32 (0.33 W/mK)+ superquilt over, taped & cross battened.

Which should give me 0.18.

The Knauff insulation is very expensive. But the only blanket  insulation that has the thermal conductivity good enough!

I think I can get PIR cheaper. 75mm would be the equivalent I think?

Are there any details out there to show calculations & alternatives?

What thickness of frametherm?

The 15% thermal bridging with timber frame means you don't get the benefit of a 32 product between the studs but there is a big cost associated with it. A 35 product will give basically the same U-value and is more cost effective.

3 hours ago, Croccy said:

Knauff frametherm 32 (0.33 W/mK)

Think you may have missed a zero.

0.033 W.m^-1.K^-1

6 hours ago, JohnMo said:

What thickness of frametherm?

90mm I think.

Can you not fully fill with 140mm frametherm? Then kill the thermal bridge with either insulated plasterboard or PIR (full sheets) batten and plasterboard.

 

Dump the super quilt.

3 hours ago, ADLIan said:

The 15% thermal bridging with timber frame means you don't get the benefit of a 32 product between the studs but there is a big cost associated with it. A 35 product will give basically the same U-value and is more cost effective.

 

To answer the last 2 replies (thank you both).

If I used a 140mm 35 product between studs. (My merchants, Huws Gray, are limited with what insulatio they can supply. Isover I think? I have a Jewsons account but they are way too expensive now)

What would my requirement be to go over the top of the studs. (thickness of PIR).

This would be the perfect scenario labour/time wise!

Try SIG, Sheffield Insulation Group, there is probably a branch near you, they were way cheaper than anyone else and I got all my Frametherm from them.

You really don’t want to buy this through a merchants, go to an online insulation supplier, or sig 

 

if you merchant is limited to what they can get, shop elsewhere, I have 3 accounts with local merchants and buy hardly anything from them, insulation superstore or equivalent. 

 

definitely ditch the silver blanket. 
 

57 minutes ago, ProDave said:

they were way cheaper than anyone else 

But try general bm too.

SIG once declined to lower their price for about 3,000m2. I told them what we had  paid on another project and they looked it up.  Ahhh, that was in xshire. We don't give that price in yshire.

It was straight from the factory in Wales ( ?) so they could have put whatever % on that they liked....so shop around.

They then said they'd match any better quote, but they didn't deserve that and lost it.

Try a national bm and a local one and SIG.

I bought nearly all my insulation online, way cheaper than BM. But prices change daily so once you find a deal buy it may be more expensive tomorrow.

By my simple calculations if I use 140mm Mineral wool 35 between studs.

I only need 40mm PIR over the top? (U value of 0.172)?

 

4 minutes ago, Croccy said:

U value of 0.172

Why go minimum U value standard? Go 70mm PIR, almost nothing lost in room size, not much more expensive, but less heat loss for years to come.