Sealing crawlspaces and insulating them with polyurethane foam

Joe Lstburek and John Tooley are both sold on sealing crawlspaces.  I saw a short bit of "Holmes Inspections" on HGTV where they sprayed 2 lb polyurethane foam directly onto the dirt floor underneath a raised kitchen addition and sealed the crawlspace essentially turning it into (semi?) conditioned space. I think they sprayed it onto the dirt, I could be mistaken.

My question is: Does it make sense to spray the foam onto the dirt so as to avoid having to install a moisture/vapor barrier, seal it with tape and them add foam on top of that and seal it with tape.

Does anyone have a good supplier of the thick white material that the East Coast companies use on their sealed crawlspaces?

Can anyone direct me to the best practices for such a project? I'm also wondering if someone has a detail for sealing and waterproofing the 12x4 vents in the stucco.

Mr. Tooley stated that sealing/insulating a crawlspace can yield a 15% energy savings. Does anyone have experience with energy savings percentages in California's Central Valley?

It seems that sealing under houses has many benefits but where are the great examples of it done right?


George Matthews

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Ground cover in the crawl space with have NO effect on foundation movement caused by soil MC. That is an exterior drainage issue.



The sealed crawlspace concept is very popular here in North carolina and surrounding states.  The best place to go for answers to your questions is and look up in their foundation sealing section.  Some thoughts regarding your questions:

  - It does not make sense to spray foam onto the dirt.  The ground is a surprisingly good insulator.  You want to insulate the peripheral walls of the crawlspace using a code-compliant R-value foam that is approved for exposed use under the Foam Plastics section of the Califormia Residential Code.  In North Carolina, Dow Thermax Sheathing rigid insulation is by far the most popular option and was the one used by Advanced Energy when they built test residences to gauge the effectiveness of sealed crawlspaces.

  - Raven Industries is the most popular manufacturer of poly to cover the ground and flash to the piers and wall insulation.

  - Advanced Energy constructed twelve test houses and determined that a home with a sealed crawlspace should produce about 18% energy savings over a home with conventional foundation vents.  Of course, that data was generated in Eastern North Carolina and results will probably differ in the Sacramento Valley.  The good news for you is that the Advanced Energy Data suggested the bulk of the energy efficiency improvement came during the warm months so some reasonable level of savings should be expected in California.  Humidity levels may impact the amount of that savings.


If you have any questions, please feel free to contact medirectly to discuss further


Scott Cummings

Sr. Technical Service Engineer

Dow Building Solutions

Charlotte, NC

I have a question about how to create a termite viewing area in a PU spray foamed foundation wall.

In crawlspace encapsulation one wants to bring the thick white plastic sheet up the foundation wall and make a nice connection with the foam (my insulation contractor does anyway). In doing that how would one create an area of 4" open clear concrete to look out for termite tunnels? Has any solved this problem?

My client who is teetering on the fence about encapsulating his unpleasant smelling crawlspace is thinking of just getting terminix out to inject termite poison into the ground around the perimeter before the project.

Anybody have a great detail for both energy efficiency and termite protection/observation? Thanks!



There's a good piece on encapsulated crawl spaces here, and it almost-but-not-quite answers your question.


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