Thursday, November 19, 2009
Do not spray foam your crawlspace foundation walls
One of the fastest growing crawlspace industries is spraying open cell or closed cell foam on crawlspace foundation walls. While I agree that foam is the most efficient type of insulation, it is rarely applicable in below-grade crawlspace environments. WHY, you might ask?. In the Midwest, crawlspaces are usually a below-grade foundation type. The foundation of a below-grade crawlspace is almost always susceptible to water and moisture intrusion from groundwater. So what, you might ask? Well, Spray foam insulation traps water and moisture in the block wall or between the wall and the foam. This moisture has nowhere to go but UP, due to the capillary action (wicking) of moisture on a foundation. Up above the foundation is a sill plate, floor joist, bandboard, and subfloor. These are all wood components that are susceptible to wood rot and mold growth when the moisture content in the wood rises.
We are in homes on a daily basis that had their foundation sprayed years earlier and now are paying thousands of dollars in structural wood repair. Most wood rot in a crawlspace is noticeable early and most of the outside wood structure is saved by some type of moisture control system. When the walls and wood are covered with spray foam, no one can detect the problem early. Homeowners do not find out until the house starts sinking and and all of the plates and joists must be replaced. The spray foam will speed up the wood rot process.
The picture above and below shows wood that has rotted behind the spray foam.
Just to be clear, every crawlspace has different amounts of moisture intrusion and some with lower levels may never have wood rot occur. However, moisture intrusion can increase over a period of years as new development pushes water into older areas. So if you still choose to foam your walls, just know, you are always susceptible to wood rot.
In below grade crawlspaces, the proper way to insulate is to encapsulate the crawlspace and seal off outside air from entering the crawlspace. Next, condition the crawlspace. Rigid Foam board can also be installed to the walls for added insulation. For more information, see my post "How to insulate a crawl space - Encapsulate and Condition"
While the title to this post seems to suggest that you should never spray foam your crawlspace foundation walls, that is not always the case. Many solid, poured foundation walls are not as susceptible to water intrusion; therefore, they could be insulated with spray foam. See my post "Insulating above-grade crawlspaces - spray foam the walls" if you have a BONE -DRY (above-grade or solid poured foundation) crawlspace.
If you need professional advice on how to insulate your crawlspace, give us a call @ 1-877-409-2837 or SIGN UP ONLINE for a FREE CONSULTATION.
Thanks for reading the rambling thoughts of a crawlspace inspector,
Larry Ralph Jr
Crawlspace Insulating Series:
Cold Floors above a Crawl Space
Do not use fiberglass insulation in a crawl space
Foundation Vents are causing higher heating costs
How to insulate crawlspaces - Encapsulate and Condition
Insulating above-grade crawlspaces - spray foam the walls