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Insulting rim joist with uncapped block foundation

I am planning on insulating the rim joist and sill plate for the entire house. I have a concrete block foundation. Some sections are capped with a smaller brick type block. Another section has a wood sill plate and other sections are simply open block at the top of the foundation. I am planning on using spray foam for the insulation to get the rim joist, a few inches of the subfloor and the top of the foundation. What should I do about the section of open block? Should I fill it with spray foam? Use rigid foam to fill each block first? Let it be? Please advise and thank you in advance.

Posted Sat, 01/25/2014 - 12:48


2 Answers

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Your spray foam contractor will "insult that no good for nuthin rim joist" and take care of the open top blocks as needed.

Answered by aj builder, Upstate NY Zone 6a
Posted Sat, 01/25/2014 - 13:11

Helpful? 0

You needn't fill the block cavites completely. Stuffing a plug of shredded fiberglass batt in the top is a sufficient stop for closed cell foam- no need for carefully sculpted rigid foam plugs. Open cell foam wouldn't even need that- just an initial spritz at the holes before going ahead with the rest. The expansion ratios are like 100:1, and it doens't take long for the droplets that caught the edges of the hole to fill in.

Block wall foundations can leak a lot of air (even below grade), and it may be worth giving it the full flash-foam treatment with closed cell foam, or full coverage rigid foam sealed at the top to your rim joist/sill sealing job.

Answered by Dana Dorsett
Posted Mon, 01/27/2014 - 16:17
Edited Mon, 01/27/2014 - 16:19.

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