0 Helpful?

Spray foam - how thick to air seal a rim joist?

What is the minimum thickness of spray foam on a rim joist for effective air sealing? I'm using a disposable 2 part 200 board foot kit.

Asked by Walter Gayeski
Posted Sep 4, 2014 10:10 PM ET

Tags:

4 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.
1 Helpful?

Walter,
Assuming you are doing a perfect job, I would put the minimum at 1 inch.

A thicker installation may allow you to be somewhat imperfect in your application technique (although it's always possible to screw up this type of work, regardless of how thick the foam is).

Answered by Martin Holladay, GBA Advisor
Posted Sep 5, 2014 5:58 AM ET

2.
1 Helpful?

New home tract built I am adding electric circuits in basement. Check this out, they sprayed closed cell on the rim joist and that's it. The thickness, 1/8-1/4".

The builders are loved for the attention to improving the lawn after you move in though... House "looks" nice, who is gonna be looking at insulation.

Answered by aj builder, Upstate NY Zone 6a
Posted Sep 5, 2014 8:09 AM ET

3.
1 Helpful?

For air-sealing purposes you can first "picture frame" it shooting a thin initial shots directly at the seams you're trying to seal, then go over it with a 1/2-1" shot directly on the major field of the wood for vapor retardency.

Even a half-inch of 2lb foam is a ~ 2perm vapor retarder that won't wick moisture during condensation events, but a mere 1/8-1/4" shot is only about as vapor tight as standard latex primer paint.

Answered by Dana Dorsett
Posted Sep 8, 2014 1:37 PM ET

4.
0 Helpful?

Who remembers Flash and Batt? I recall articles illustrating moisture and mold problems in wall cavities where the foam is less than 2 inches. Why would this application be any different when the foam is less than 2 inches? Aside from the perm rating any thickness will block air flow. The risk of moisture and mold is another issue to consider.

Answered by Richard Beyer
Posted Sep 8, 2014 1:55 PM ET

Other Questions in General questions

Dense packing cellulose - height of cavity

In General questions | Asked by Graham Fisher | Feb 28, 15

Best way to have a wood fireplace?

In Energy efficiency and durability | Asked by Clara Kim | Feb 22, 15

Multi split with ceiling fans?

In Mechanicals | Asked by alok khuntia | Feb 27, 15

Foil-faced batt insulation effect on wall construction?

In GBA Pro help | Asked by Michael Kalustov | Feb 27, 15

Recommendation for minisplits vs. gas-fired HVAC for new Massachusetts building

In Mechanicals | Asked by Bill Perkins | Feb 25, 15
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!