Isover Frame Batt 32 not recommended for between rafters

[Thorfun]

I was speaking to Isover technical department today to get a condensation analysis on my roof make up and when I said I was using 140mm and 50mm ISOVER Timber frame batt 32 to give me 190mm of insulation between the rafters they said that between the rafters they recommend Isover Metac (https://insulation-uk.com/products/isover-metac) as it was designed to go between the rafters and the frame batt may not be self-supporting.

 

this surprised me and I've already bought the frame batt 32 so to change to Metac now would be a costly mistake.

 

I believe that there are many on here that have used the timber frame batt 32 (and 35) between their rafters although it does seem like many use Knauff products. Anyone ever had issues with using timber frame batts between the rafters?

 

I am putting 100mm PIR below the rafters so would think that would hold the glass mineral wool in place and would presume that the timber frame batts do not slump otherwise they'd not work in walls.

 

do I just crack on or speak to the BM about returning the frame batts and going with the Metac?

[ProDave]

Frametherm 35 was self supporting between rafters in my case.  It only had to self support long enough to get the OSB sheets on, but one trial piece sat there for 6 months without sagging.

[Thorfun]

2 minutes ago, ProDave said:

Frametherm 35 was self supporting between rafters in my case.  It only had to self support long enough to get the OSB sheets on, but one trial piece sat there for 6 months without sagging.

thanks Dave. I remember reading your blog and posts about it which is why I'm sure it won't be an issue but when the company says things like

 

"As the Isover Timber Frame Batt 32 is designed for timber framed walls, we do not have any test data to support this within the pitched roof application.
 
Thermally, it would be acceptable but you will need to ensure that there is no risk or slumping and it stays in position once installed."

 

that makes me think that there's no BBA certification for between rafters and I will need to check with BCO if it's acceptable.

[ADLIan]

Don't see what the problem is - if its OK to be used vertically why not at an angle? Only has to support itself until the ceiling finish goes in as ProDave says. Perhaps they make more money on the Metac!!

I also doubt lack of BBA certification will be an issue and never had a problem with this construction as the application is covered in the Appr Docs and relevant British Standards

[Thorfun]

14 minutes ago, ADLIan said:

Don't see what the problem is - if its OK to be used vertically why not at an angle?

exactly what I said to them but they had slopey shoulders and carried on with the 'not recommended' line of answer.

 

15 minutes ago, ADLIan said:

Only has to support itself until the ceiling finish goes in as ProDave says.

yep. again that's what I said!

 

15 minutes ago, ADLIan said:

Perhaps they make more money on the Metac!!

ahhh...someone who is just as cynical as me. ?

 

[Thorfun]

so the BM will take the frame batts back but the Metac will cost me an extra £600 when compared to using the frame batts and is on a long lead time (probably not available this side of Christmas) so I think I know what my decision is going to be!

 

it's just so hard to quiet the voice at the back of my head that tells me I'm doing it wrong. ?‍♂️

[ADLIan]

It’ll be fine. Crack on. £600 extra??? No wonder we’re cynical!