Anyone have this product? The walls are no issue. Just sprayed on against the RAB . Ceilings they want to spray it on the underside of the roofing underlay. Not sure if thats a good idea or not.
mrgts4,
Feb 6, 7:25am
No way, definitely not a good idea to spray on the underside of roof underlay. Why would a new house need a spray foam insulation, whats wrong with traditional insulation?
martin11,
Feb 6, 7:48am
Does it meet the insulation requirements in the area for the walls ?
tweake,
Feb 6, 9:08am
afaik spray foam needs to go against something solid. also afaik underlay you don't want insulation touching it, there is typically a gap under it before the insulation.
whats in the plans? this should have been decided on at planning stage and should be on the plans.
spray foam does have an advantage with air sealing, but you need to do all the other details to make that work. you need to have a sheathed roof for starters and seal up all the air leaks the spray foam won't get to.
dastedly,
Feb 6, 8:53pm
The form is good stuff ,But if there is a fire then very bad stuff
denlah,
Feb 7, 8:20am
Looked at spray foam to replace the batts in my 120 Sqm ceiling but the price quoted was horrendous and they stipulated that if the roof angle at the eaves was to tight they would have to pull the ceiling gib extra costs. I thought they didn't want the job.
tweake,
Feb 7, 8:30am
i'm not sure on exact pricing, but afaik spray foam is more expensive than traditional batts, especially closed cell foam. pulling the ceiling gib doesn't make any sense as thats what they would be spraying it on to. they would have to pull the roofing off.
claire351,
Feb 9, 6:57am
Just trying to increase the insulation value . Considering the amount of timber in the walls .
tweake,
Feb 9, 7:31am
is this on a building in progress or just in design phase?
don't use closed cell foam as its too vapour resistant. if you have a lot of timber you may be better to look at thermal break, ie external insulation. there is one you can use instead of RAB board.
one issue i see in a lot of "designer" homes is huge amount of glass so they have a huge amount of support structure, very little space for insulation and has massive thermal bridging.
tygertung,
Feb 9, 8:49pm
I don't think it is a good idea to have a house hermetically sealed as then it won't breathe very well and it will be difficult for any moisture to escape.
I think this may have been a problem in the 90s when moisture could get in through cracks, but there was not enough airflow so it couldn't get out and there was issues with mold and even rotting wood in the framing.
tweake,
Aug 19, 12:57pm
yes/no.
"breathe" is the wrong term. walls have absolutely no need to breathe air whatso ever. but houses must "breathe" which is why we have ventilation, ie open a window.
moisture moves through timber and other materials. its a bad idea to stop it. things like 90's EIFS is polystyrene which lets very little amounts of moisture through it, its a really dumb idea to fix that to the framing. but leaky homes is more about the idea that you can make a house "water proof".
there is exterior insulation which does allow moisture to move through it.
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