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Old 01-04-2009, 05:18 PM   #1
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seal gaps in attic


Hi. How do I seal the gaps in my attic? CAn I use the "foam spray" great stuff...thanks

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Old 01-04-2009, 05:33 PM   #2
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seal gaps in attic


What gaps are you you thinking of sealing?

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Old 01-04-2009, 09:18 PM   #3
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seal gaps in attic


I just finished sealing my attic last night. The great stuff works well, but get the 'Fireblocker' in the tall orange can. I couldn't find it at Lowe's, but Home Depot has it for just under $10 a can. It won't work very well though if your attic temp is under 45-50 degrees F. The company says they don't suggest using it under 40F because it won't expand and set-up properly. There is also fire blocking caulk available, but one can of the foam equals about 10 or 15 cans of the caulk.

I let the warm air from the house flow up there most of the day through the hatch to bring the temperature up. When I used it last night, the temp up there was around 45 degrees, so the foam would flow out of the can really well for a few minutes and then slow down to where it was just barely coming out. I filled the bathroom sink with warm water and let the can sit in there for 5 minutes or so. Then the foam would come out really well again for a few minutes. I hated to do it this way, but I was almost done and didn't want to wait until spring to finish. Also, the straws that come with the can of foam break fairly easily when it's cold. The foam did expand and set up properly though. Today I used a serated knife to cut the excess foam off so that the batts of insulation would lay flat without any gaps under them. I didn't cut the stuff near the electric wires, just the excess from filling the gaps between the side of a top plate and the drywall.

If you have any hot pipes coming up through the attic floor, you shouldn't use Great Stuff to fill the gaps around them if the pipe reaches a temp of 240F or more. An HVAC guy might be able to tell you what to use around the hot pipes. Have fun
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Old 01-04-2009, 10:34 PM   #4
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Originally Posted by gma2rjc View Post
I just finished sealing my attic last night. The great stuff works well, but get the 'Fireblocker' in the tall orange can. I couldn't find it at Lowe's, but Home Depot has it for just under $10 a can. It won't work very well though if your attic temp is under 45-50 degrees F. The company says they don't suggest using it under 40F because it won't expand and set-up properly. There is also fire blocking caulk available, but one can of the foam equals about 10 or 15 cans of the caulk.

I let the warm air from the house flow up there most of the day through the hatch to bring the temperature up. When I used it last night, the temp up there was around 45 degrees, so the foam would flow out of the can really well for a few minutes and then slow down to where it was just barely coming out. I filled the bathroom sink with warm water and let the can sit in there for 5 minutes or so. Then the foam would come out really well again for a few minutes. I hated to do it this way, but I was almost done and didn't want to wait until spring to finish. Also, the straws that come with the can of foam break fairly easily when it's cold. The foam did expand and set up properly though. Today I used a serated knife to cut the excess foam off so that the batts of insulation would lay flat without any gaps under them. I didn't cut the stuff near the electric wires, just the excess from filling the gaps between the side of a top plate and the drywall.

If you have any hot pipes coming up through the attic floor, you shouldn't use Great Stuff to fill the gaps around them if the pipe reaches a temp of 240F or more. An HVAC guy might be able to tell you what to use around the hot pipes. Have fun

do you have a vapour barrier on your ceiling?...
did you fill in all the gaps (including the ones that are in between the ceiling floor and the vent stack? what about ones that are in between light fixtures and the ceiling? thanks
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Old 01-04-2009, 10:35 PM   #5
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seal gaps in attic


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What gaps are you you thinking of sealing?
the gaps in between the vent stack and the ceiling of the attic...and the light fixture hole and floor ceiling...and the exahust fan-box and the floor of the ceiling...basically, anywhere where there is "daylight" where I can see into the 2nd floor below the attic floor...
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Old 01-05-2009, 12:06 AM   #6
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do you have a vapour barrier on your ceiling?...
There wasn't one up there, and I ended up not putting one in, but I wish I could have. The reason is that there are spots up there that I cannot reach well enough to put down and properly tape a vapor barrier. Since I can't cover all of it, it made no sense to do any of it. I was also told that the paint in the rooms below serves as a vapor barrier (although not as good as 6mil poly). The paper backing on the batts of insulation are suppose to serve as a vapor barrier also, although I can't imagine it would be very good since the edges are only stapled, not taped, which allows some moisture to get through. If I was starting from scratch I would put the vapor barrier up and tape every seam before drywalling.

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did you fill in all the gaps (including the ones that are in between the ceiling floor and the vent stack? what about ones that are in between light fixtures and the ceiling?
I filled every gap I could reach. The vent stacks were the hardest to reach, but I was finally able to use the spray foam and fill those gaps. At first, I didn't think there were any ceiling fixtures, but there was one for a ceiling fan and one for a hallway light. But even though I couldn't see a gap around either of them, I still sprayed a little foam around each round box just in case there was a little air coming through. I found all of the wall top plates and filled every hole that had a wire coming through it and there were also a few holes that had no wires. Last night when I went up there, I thought it would take me an hour at the very most (Ha!). But when I started moving the batts of insulation around looking for wiring holes, I found that there were long gaps along the sides of each top plate where they meet the drywall. I ended up spray foaming along both edges of every top plate. It wouldn't be so bad if the pitch on the roof wasn't so low.

You'll want to fill every gap you find. If there is one you're not sure about, ask someone here before you fill it. Are you going to put down a vapor barrier? It's a good idea if you can do it. Although, in some parts of the U.S. it's not recommended. If you go on the Department of Energy website, I think they have a map that tells whether or not you need a vapor barrier. Do you have baffles and vents in your attic already? Is your bathroom fan(s) vented to outside the house?


Table 1. Locations of Attic Air Leaks and Sealing Methods
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Old 01-05-2009, 01:05 AM   #7
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seal gaps in attic


i believe the only difference between regular foam and the fireblock is the color
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Old 01-05-2009, 07:01 AM   #8
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i believe the only difference between regular foam and the fireblock is the color
I believe you are correct. They are both "Minimal Expanding Polyurethane Insulating Foam Sealants". But only the Fire Block foam is tested and approved for sealing fire and smoke penetrations.

Just to clarify for code-approval purposes:

"Great Stuff" brand, the "Gaps & Cracks", "Big Gap Filler", & "Windows & Doors" foams are UL classified as a "sealants".

The Great Stuff "Fire Block" foam is colored for "code-identification". But unlike the other foams, it is tested and approved for "Impeding the spread of fire and smoke through service penetrations". - UL Classified ASTM E84, ASTM E814 (modified), UL 1715
http://www.techstreet.com/cgi-bin/de...uct_id=1034383
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Old 01-05-2009, 07:06 AM   #9
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For filling gaps around smoke stacks, the required materials should be high-heat rated. Examples: Fire-rated insulation and a high heat-rated sealant.
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Old 01-05-2009, 08:55 AM   #10
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I believe you are correct. They are both "Minimal Expanding Polyurethane Insulating Foam Sealants". But only the Fire Block foam is tested and approved for sealing fire and smoke penetrations.
Then it's probably not worth paying double for the fireblock if it's just a difference in color. Where would wilsonfrench get the fire-rated insulation or high heat-rated sealant?
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Old 01-05-2009, 09:07 AM   #11
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...Where would wilsonfrench get the fire-rated insulation or high heat-rated sealant?
Fire rated insulation: Roxul - http://www.rockwool.us/sw34066.asp
A Building Supply/Lumber Yard place should have it. Call around and ask, rather than waste gas and time, looking for it.

High heat sealant: Big Box stores should have it in their wood stove/fireplace areas. Also fireplace/wood stove stores should carry it.

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