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rigid foam board with fiberglass backing on both sides


rmcfall's Avatar
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12-20-09, 07:27 AM   #1  
rigid foam board with fiberglass backing on both sides

I came across some "seconds" of rigid foam board today. The foam board was 1" thick 4x8 sheets and the seller called it roofing foam. It looked like polyisocyanurate, but with a fiberglass backing on both sides. The price was good-- $350.00 for 48 sheets. However, I was afraid of the fiberglass backing on both sides. Also, the sheets weren't flat from where they have been outside, but I imagine they would go back to flat again? Can this sort of foam be stacked together in layers even though it has the fiberglass backing? Problems with moisture/mold? Can it be used along basement walls?

 
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12-28-09, 01:42 PM   #2  
Strangely the first time I heard about this was about 6 hours ago. i read of a guy who seemed to know a good bit, he had put it in his basement and after some time had to rip a bit of the wall down for plumbing and found that this stuff had performed well without mold issues. I have no idea where I found the thread or how I found it unfortunately

 
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01-04-10, 09:40 PM   #3  
This does sound like plyiso. I am using it in a cathedral ceiling; three layers of 2 inch. I purchased new and have been assured by the manufacturer and saleperson that the fibreglass is not a vapour barrier and that therefore it can be stacked without problems i.e it will allow vapour to flow through. The foil backed is a different story. I find it does flatten and that is a great price by the way.

 
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01-05-10, 05:36 AM   #4  
Where did you find this stuff? I haven't seen it anywhere else locally... Who is the manufacturer?


Posted By: hironomous This does sound like plyiso. I am using it in a cathedral ceiling; three layers of 2 inch. I purchased new and have been assured by the manufacturer and saleperson that the fibreglass is not a vapour barrier and that therefore it can be stacked without problems i.e it will allow vapour to flow through. The foil backed is a different story. I find it does flatten and that is a great price by the way.

 
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01-05-10, 04:08 PM   #5  
I'm in Canada (Saskatchewan) and got it at a roofing supply store. I think it is a chain you might also have called "Roofmart". It is called "IKOtherm" and produced by IKO.

Really easy to work with, as it cuts like butter with a jigsaw, handsaw or circular saw, but man those fibres are nasty - wear gloves and eye protection. I sealed the edges with spray foam (which sort of defeats any environmental advantage). As per a post on another thread, I found that leaving a 1/4 inch gap made it easier to fill than trying to cut them precisely.

I am not sure it responds as well to direct moisture (i.e. directly against concrete in a basement wall) as poystyrene, but you could likely email IKO and ask. They were great about responding to me. As I said, I was assured that the foam and facing are vapour permeable and so o.k. stacked within the wall (or ceiling in my case) cavity.

 
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01-05-10, 05:26 PM   #6  
Just curious...did you fill the entire depth of the gaps, or just fill it enough to seal things things up? That is, if the 1/4" gap is a total of 6 inches deep, did you fill the entire 6 inches or just the initial inch or so?



Posted By: hironomous As per a post on another thread, I found that leaving a 1/4 inch gap made it easier to fill than trying to cut them precisely.

 
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01-05-10, 05:32 PM   #7  
Posted By: rmcfall Just curious...did you fill the entire depth of the gaps, or just fill it enough to seal things things up? That is, if the 1/4" gap is a total of 6 inches deep, did you fill the entire 6 inches or just the initial inch or so?
I used this approach and personally aimed to do more along the lines of filling 6" deep as opposed to just a seal. This was at my rim joists where I was using 2" chunks of foam so it's no big deal to make it as deep as that.

 
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01-05-10, 06:32 PM   #8  
I did each layer separately, since I figured any cold air getting betwen layers would deccrease the insulating value, so I only had two inches to fill at a go. Cause the foam expands so much, if you get it into the crack, it pretty easily fills an inch or two of depth,

It goes a long way, but I still used a lot of cans. The foam is strong enough to move the sheets though, so it proved important to fasten them well to the studs (I used drywall screws). All of this adds to the cost. If you want to maximize your savings and insulating value, you might be best to fill the cavities with batts and use the foam sheets as a layer over the studs to provide a thermal break.

 
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