# Basement Rim Joist in CT



## Windows on Wash (Aug 30, 2011)

I'm not aware of any code requiring R-30 at the rim for your zone.


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## Bud9051 (Nov 11, 2015)

Hi son,
I looked up CT as a zone 5 area and if you look at floor R-value for floors it shows R-30. However, note "g" says "Or insulation sufficient to fill the framing cavity. R-19 is minimum." He is probably thinking that refers to the rim cavity, when in fact that note is in reference to a fully insulated floor with a cold basement or crawlspace.

A rim cavity as part of a finished, insulated, and heated basement would be the worst a wood framed wall at R-20. Talk to them again to clarify what is required and if you can meet that with a combination of rigid plus batt insulation.

An additional note would be to go crazy air sealing the sil plate to the foundation plus all seams. Some use the can foam, but I prefer an inexpensive caulking or even construction adhesive. Foam may have a shorter performance life than a caulk and I have some stray gobs of construction adhesive that will take a grinder to remove.

Here is the link for the 2009 energy codes I referenced.
https://energycode.pnl.gov/EnergyCodeReqs/

Bud


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## Gary in WA (Mar 11, 2009)

I agree to use some caulking on the wood rim/joist/floor sheathing joints to flex and remain the air-seal you need before adding the foil-faced foamboard which stops both interior/exterior moisture from forming on the rim/insulation interface to dry the rim quicker. Unfaced XPS will keep moisture against the wood longer, also taking longer to dry during the springtime/summer months. Without air sealing the rim, you would have trouble meeting any house/addition pressure test- now required in many locales per newer Energy Codes, pp.16; https://www.energycodes.gov/sites/default/files/documents/BECP_Buidling%20Energy%20Code%20Resource%20Guide%20Air%20Leakage%20Guide_Sept2011_v00_lores.pdf

Gary
PS. IMO, caulk is flexible to move (and still air-seal) with the RH of the wood swelling/contracting during seasonal changes when adhesive wouldn't.


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## Gary in WA (Mar 11, 2009)

If the unfinished rooms are to remain unfinished/unheated, then the floor R-values would be in force. This is your thermal boundary. If the rooms are heated, the R-values of the rims would be for walls; many pics- http://www.nrel.gov/docs/fy13osti/55802.pdf

Gary


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## sonofbuster (Feb 23, 2015)

Thanks for the replies and links. I emailed a request for more info past "R-30" from the last email, but in the meantime I'll do some reading. Thanks again.


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## Crazyjake8493 (Sep 26, 2014)

R-30 would be overkill, he most likely looked at the R-value for floors. Not sure what the code says exactly, but the general rule of thumb that I've heard and gone by is rim joists should match the R-value of the exterior walls. My walls and rim joists are both R-13.


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