Spray foam insulation

Agri contractor

We are building at the moment and looking at insulation for the attic. I am looking at spray foam insulation. I have phoned a few companies, all telling me they have the best product. All of them are working on open cell. Did anyone use this type of insulation ? any help would be appreciated.

BryanF

ive concerns are about the fumes and off-gasing, but i suppose thats no different than the PIR/PUR's... my preference is for cellouse, hemp or a natural material. from talking to installers there are some major discrepancies between what is quoted by them and what actually stated in the IAB / BBA certificates.

my advice is to have your architect read the fine print very carefully especially as regards Breathable felt and Vapour barriers.

there's a very long thread here somewhere (maybe a mod could point to it) where spray foam was discussed at length.

mickdw

From experience, the Spray foam companies will spray anywhere if there is a fee in it for them. They take no notice of what they are working with, whether suitable membrane is used, ventilation requirements etc. Proceed with caution.

Agri contractor

The problem I am told is when the foam is sprayed between the truses the felt is pushed on to the slate. I haven't been able to find much info on this.

sydthebeat

Agri contractor wrote: »

The problem I am told is when the foam is sprayed between the truses the felt is pushed on to the slate. I haven't been able to find much info on this.

thats one issue.

if you can picture felt on rafters.. it sags between them rafters. this creates a natural channel for any moisture to run down...

if the foam is sprayed between the rafters then obviously this 'channel' is inverted and the water runs down that section which is now over the rafters. So this locates moisture in the exact location you dont want it located...

over the structural timber and along nail points....

other issues include the common lack of a vapour barrier installation, and the fact thats its u value isnt much better than standard quilted material.

derealbadger

First I am a spray foam contractor so as no body can say I am trying to be disingenuous, there are 3 foam manufacturers with N.S.A.I certs and to meet with N.S.A.I certifications they can not be sprayed directly onto felt and must be fitted with a card leaving a gap between the felt and the insulation

sydthebeat

thanks derealbadger.

can you confirm if there is or not nsai certs for spraying foam insulation either into cavity blocks, or into a cavity wall?

derealbadger

sydthebeat wrote: »

thanks derealbadger.

can you confirm if there is or not nsai certs for spraying foam insulation either into cavity blocks, or into a cavity wall?

No SPF is certified by N.S.A.I for use in cavity wall or in cavity block but as you say there are company's doing both most of the cavity block that is being done with foam is not with polyurethane but with a urea based foam

Vicbowling

sydthebeat wrote: »

thats one issue.
other issues include the common lack of a vapour barrier installation, and the fact thats its u value isnt much better than standard quilted material.

If you are worried about spray foam insualtion vapor barrier, use a closed cell polyurethan spray foam inuslation. They do have some vapour retarder qualities. I'm no expert on it. But have donre some research for my own project. derealbadger may not agree.

derealbadger

Vicbowling wrote: »

If you are worried about spray foam insualtion vapor barrier, use a closed cell polyurethan spray foam inuslation. They do have some vapour retarder qualities. I'm no expert on it. But have donre some research for my own project. derealbadger may not agree.

Closed cell is great in the right places but not for full fill of rafter for the very reason you have pointed out yourself it is a vapour/water proof but that also means that it is not breathable so you need to remember that your rafters have to be able to breath and again going back to certification only open cell foam has N.S.A.I cert for use in domestic attic

sydthebeat

Vicbowling wrote: »

If you are worried about spray foam insualtion vapor barrier, use a closed cell polyurethan spray foam inuslation. They do have some vapour retarder qualities. I'm no expert on it. But have donre some research for my own project. derealbadger may not agree.

yeah, i wouldn't be happy surrounding a piece of structural timber in a vapour closed material.....

all you are doing is focusing any vapour / moisture into the structural timber because they are more breathable than the insulation. Thats a recipe for disaster.