Rim Joists and Vent duct insulation

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Tyler R
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Rim Joists and Vent duct insulation

Post by Tyler R » Thu Jan 03, 2019 3:29 pm

20190103_140918.jpg
Floor Vent Duct
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Hey guys! First time posting! Shannon I love all of your videos, they have helped me through a lot. What brings me here now are two questions, one is rim joist insulating. I have watched the videos with fibreglass/poly which looks terrible, also watched the 2" rigid insulation with low expansion foam one. I am between those two methods as spray in is not an option financially. What the question is, which method is best with what I've got? Rigid needs roxul still due to fumes generated when burning, so does that being cost way up using that method? Is just using fibreglass and going through the pain of poly and acoustical sufficient just terrible to do? Having a hard time deciding. The second question is how can I insulate around that vent ducting? Old build had insulation tucked in behind it, no vapor barrier. Can I use cans of low expansion foam? Can I use fibreglass and poly over without it melting or anything? Looking for the answer that doesn't include moving it to an interior wall as there are three and it's a PIA. Thanks in advance!!
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Rim Joist
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Tyler R
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Joined: Thu Jan 03, 2019 3:16 pm

Re: Rim Joists and Vent duct insulation

Post by Tyler R » Thu Jan 03, 2019 3:32 pm

Pictures are sideways for some reason, sorry.

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Shannon
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Re: Rim Joists and Vent duct insulation

Post by Shannon » Thu Jan 03, 2019 5:37 pm

So for the joist ends that are infilled with concrete you could actually install foam across the top of the concrete (in that top gap) fill above it with canned foam to seal . Then install a horizontal piece lapping back onto the top of the framed wall plates about 2" and back to the concrete.Finally a vertical piece on top of that horizontal piece right to the bottom of the sub floor above. Push this piece back against the concrete and then seal all gaps and joints with canned foam. You can then place batt insulation in to fill the remaining space. As long as you are installing a ceiling you usually would not need to cover the foam with Roxul, check with your local codes.

Batt insulation and sealed poly works also but it is tough to get a perfect seal.

With that duct if you can get a sheet of foam between it and the concrete wall that would be great. You will loose a lot of heat value in winter once the air travels through that duct. Otherwise you can seal in beside it with canned sprayfoam. You also can poly over it. There will never be enough heat to melt poly against duct.
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Tyler R
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Joined: Thu Jan 03, 2019 3:16 pm

Re: Rim Joists and Vent duct insulation

Post by Tyler R » Sat Jan 05, 2019 10:58 pm

Shannon wrote:
Thu Jan 03, 2019 5:37 pm
So for the joist ends that are infilled with concrete you could actually install foam across the top of the concrete (in that top gap) fill above it with canned foam to seal . Then install a horizontal piece lapping back onto the top of the framed wall plates about 2" and back to the concrete.Finally a vertical piece on top of that horizontal piece right to the bottom of the sub floor above. Push this piece back against the concrete and then seal all gaps and joints with canned foam. You can then place batt insulation in to fill the remaining space. As long as you are installing a ceiling you usually would not need to cover the foam with Roxul, check with your local codes.

Batt insulation and sealed poly works also but it is tough to get a perfect seal.

With that duct if you can get a sheet of foam between it and the concrete wall that would be great. You will loose a lot of heat value in winter once the air travels through that duct. Otherwise you can seal in beside it with canned sprayfoam. You also can poly over it. There will never be enough heat to melt poly against duct.
Thanks Shannon! I have a question though... You say use a "horizontal piece'' then a "vertical piece". What are you referring too? Fibreglass? Sorry I'm not following. I'm good up until after the canned spray foam lol.

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Shannon
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Re: Rim Joists and Vent duct insulation

Post by Shannon » Sun Jan 06, 2019 12:45 pm

Horizontal and vertical rigid foam. The reason I say in that order is because the joint between the two is easier to see and fill with canned foam after.
Does that clear it up?
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Tyler R
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Re: Rim Joists and Vent duct insulation

Post by Tyler R » Sun Jan 06, 2019 4:25 pm

Shannon wrote:
Sun Jan 06, 2019 12:45 pm
Horizontal and vertical rigid foam. The reason I say in that order is because the joint between the two is easier to see and fill with canned foam after.
Does that clear it up?
Yes! Like this? See my cheesy drawing.
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Re: Rim Joists and Vent duct insulation

Post by Shannon » Sun Jan 06, 2019 4:31 pm

yup exactly. Remember to spray foam joint in rigid foam, all edges and between top wall plate and rigid as well.
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