Bio based Spray Foam insulation

nmc1971

Hi,
I've seen some older threads asking for advice on Spray Foam insulation, but I was hoping to get some up to date advice on from anyone whose used this in a timber frame build ?

I have 100m2 of a pitched roof with 160mm rafters, with plywood, felt, batten and slates. 70m2 of exterior wall with plywood, felt, and cement board exterior.

Any suggestions, advice, tips or snags for going with spray foam as opposed to Kingspan would be very welcome !

thanks
Nmc

PeteHeat

Hi,

One thing that would concern me about sprayed foam is there is no space for the timbers to breathe.

If you fit Kingspan or similar you can leave a space between the insulation and the plywood which will allow air to circulate and prevent moisture from passing through to the structure.

slavetothegrind

PeteHeat wrote: »

Hi,

One thing that would concern me about sprayed foam is there is no space for the timbers to breathe.

If you fit Kingspan or similar you can leave a space between the insulation and the plywood which will allow air to circulate and prevent moisture from passing through to the structure.

Just a question. Is the foam impermeable? I thought it was..but i don't know.

nmc1971

PeteHeat wrote: »

Hi,

One thing that would concern me about sprayed foam is there is no space for the timbers to breathe.

If you fit Kingspan or similar you can leave a space between the insulation and the plywood which will allow air to circulate and prevent moisture from passing through to the structure.

Thanks PeteHeat,
There should be a gap as the rafters are 160 mm and I was planning on filling the foam to 140mm or slightly less. The product says it allows air to breath through it.. don't ask me how! I have a great builder on site at the moment, tasty timber frame guys and they swear by this stuff !

Anyone else with any direct experience with Econstructsystems or Ecoseal, I'd again appreciate any advice .

cheers
Nmc

nmc1971

joeclif wrote: »

Just a question. Is the foam impermeable? I thought it was..but i don't know.

Hi Joe,

It acts as a vapor barrier but not an air barrier ..

GreeBo

Im confused. If it lets air pass through it, then how is it insulating?
Surely the hot/cold air will just pass through it then?

nmc1971

GreeBo wrote: »

Im confused. If it lets air pass through it, then how is it insulating?
Surely the hot/cold air will just pass through it then?

Sorry.. my mistake.. it is of course and air barrier but not a vapour barrier.. my understanding of this is that it manages moisture from the inside to the outside.

PeteHeat

Hi,

I expect the companies applying the products have carried out the research, my experience is with possibly older technology where a company in Dublin was spraying foam under old slate roofs.

The idea was spray the underside (no felt / breather membranes) the benefit was supposed to be, insulate the roof and stop slates from slipping basically it was a miracle cure.

The problems arose after about five years because the roofs could not breathe, timber rot was a major problem for a number of reasons.

I may need to brush up on application procedures I can't understand how a 50mm air gap will be left between the foam and the plywood.

GreeBo

nmc1971 wrote: »

Sorry.. my mistake.. it is of course and air barrier but not a vapour barrier.. my understanding of this is that it manages moisture from the inside to the outside.

Whew, Im not going mad then!
Spray foams are effectively like insulating with a sponge. The medium can soak/wick water but air cannot pass through. Though I think there are some waterproof foams now, but not 100% sure.

gman2k

I have bio-based spray foam insulation in my timber frame house.
PM me for further details.