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Waste of time sealimg rim joist in a walkout basement?


Tony P.'s Avatar
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CT

02-08-18, 06:43 AM   #1  
Waste of time sealimg rim joist in a walkout basement?

I have an uninsulated basement 55% concrete and 45% walkout and am starting a substantial project to add insulation to the walkout and seal the rim joists. I will not be sealing the walkout walls due to cost issues.

My question relates to sealing the rim joists over the walkout portion. This appears to me to be similar to sealing rim joists between a first and second floor. As I will be insulating but not sealing the walkout walls, I am wondering whether it's worthwhile or just a waste of time to seal the rim joists in that walkout area by applying 2" XPS to the rim joist. It strikes me that air from the walkout wall will move up from the walkout wall, irrespective of the XPS.

Note, I'm asking only about the rim joist over the walkout, not the typical rimjoists over sill plates.

Thoughts, please.

 
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XSleeper's Avatar
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02-08-18, 06:49 AM   #2  
You would treat it just like every other rim on the house.

 
Tony P.'s Avatar
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02-08-18, 07:03 AM   #3  
You would treat it just like every other rim on the house
Do builders typically seal rim joists between first and second floors and not the walls to the floors, themselves?

 
XSleeper's Avatar
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02-08-18, 07:23 AM   #4  
Are you asking about where a wall sits on top of a subfloor? If not, I don't understand the premise of your question at all. There is no difference. All rim joists are insulated the same way. It doesn't matter where they are, they are all built the same.

Walls have a top plate that separates the floor joist space from wall space. If you don't air seal the rim joist, exterior air can travel down the floor joist cavity just like it's a duct because that cavity is not completely filled with insulation like a wall is. And the foam is far superior to fiberglass when it comes to air sealing. The perimeter foam provides that air barrier.

 
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