jsmith6752
Well-known member
I just picked up some 1 1/2" foam board made by Firestone. It is used in roofing applications. It is ISO 95+GL. I want to use it under a floating slab. Do you think I can get by with it? thanks
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Firestone
- Thread starter jsmith6752
- Start date
rburke65
Well-known member
I just looked at this stuff as there was a large dumpster filled with this stuff in a mall parking lot. They were replacing the roof on a JC Penneys. I had no idea what it was called until now. I just Google it and found that it has a compressive strength of >138kpa and the conversion equates to a compressive strength about 18 psi. I think the recomendated psi is 25 psi so I think that you and I are SOL. But, just my opinion. No HVAC guy here.....just an Electrician. But I have read that you only need 15psi in reality. At 15 psi, that's 2160 psi over a square foot....That is a lot of weight that this stuff can handle.
Last edited:
OP
jsmith6752
Well-known member
Who's to say it could be used as perimeter insulation.
OP
jsmith6752
Well-known member
option 2 With an R9 rating it should be ok for the ceiling. I was thinking about laying it on top off the rafters which are 2' on center. I was going to buy the 1/2" foam board with foil as my ceiling. At $13 for a 4 x 8 sheet for the Firestone it seems logical to go that route. I want to install vinyl soffit material (as I saw on another post) for the entire ceiling. Any thoughts? thanks
I don't know if i would do that. There is a reason they sell proper insulation for ceiling.
ISO board is great when you do bitumen roofing because it gives the roof / rubber/ mod bit, whatever a cushioned surface, while adding insulation to a flat roof deck.It's more of a decoupling method from the roof deck really. The R value of it is just not enough to be the sole insulation method.
1. The iso board doesn't expand or contract like the wood, so you will get gaps and bulges with temperature changes if you screw it in place.
2. If you just lay it, make it floating, it will deform. the corners raise up and it just won't look nice, or make a useful seal.
3. R9 is a little weak for ceiling. I like R30 and higher. R40 and up is what I recommend all the time.
4. Find some proper insulation. I recommend Roxul for its ease or use, cutting, and no damn itching all over you body for a week. It will cost a bit more, but you get around 40sq ft, much higher R value. Iso board is not that cheap if you think about it.
ISO board is great when you do bitumen roofing because it gives the roof / rubber/ mod bit, whatever a cushioned surface, while adding insulation to a flat roof deck.It's more of a decoupling method from the roof deck really. The R value of it is just not enough to be the sole insulation method.
1. The iso board doesn't expand or contract like the wood, so you will get gaps and bulges with temperature changes if you screw it in place.
2. If you just lay it, make it floating, it will deform. the corners raise up and it just won't look nice, or make a useful seal.
3. R9 is a little weak for ceiling. I like R30 and higher. R40 and up is what I recommend all the time.
4. Find some proper insulation. I recommend Roxul for its ease or use, cutting, and no damn itching all over you body for a week. It will cost a bit more, but you get around 40sq ft, much higher R value. Iso board is not that cheap if you think about it.