Thursday, November 19, 2009
Insulating above-grade crawlspaces - spray foam the walls
For those who do not know, a crawlspace above grade refers to a crawlspace with a ground floor that is level with the outside ground level. In many instances, these crawlspaces can be considerably dry. Since many crawlspace above grade are somewhat dry, the best method of insulating is to encapsulate with plastic and apply spray foam to the walls and exterior wood framing. I am a large advocate of the foam method of insulating; however, only when the conditions are optimal (a dry crawlspace). The biggest mistake a homeowner can make when insulating a crawlspace is to spray foam the foundation wall when it is wet or damp. The foam will trap the moisture in the foundation allowing it to rot the structural components such as the sill plates, floor joist ends, and bandboard. For more information on whether you should spray foam your crawlspace walls, see my post "Do not spray foam your crawlspace foundation walls".
The proper method to insulating a DRY crawlspace is to first encapsulate the ground moisture and seal off outside air. This is achieved by installing 20 mil plastic over the ground floor and up the walls by at least 12". (Warning: Encapsulation liners should normally be installed within 3" of the top of the foundation wall, but since the crawlspace foundation is dry and we will be applying spray foam to the walls, there will be no need to.) All the seams of the liner should be taped, and the wall plastic should be fastened and adhered to the foundation wall. Once the encapsulation liner is installed, all of the foundation vents should be insulated and sealed. Sealing the foundation vents prevents cold, freezing air from entering the crawlspace in the winter (cold air still drafts in even when the vents are closed); and hot, humid air from entering in the summer. This is by far the most important step in insulating a crawlspace, and if you didn't do anything else, you could look at 10% - 15% energy savings in a fully vented crawlspace by just encapsulating. Once encapsulation is finished, the crawlspace can be conditioned.
The next step would be to hire a contractor to spray the interior crawlspace foundation walls and wood framing with closed cell foam. They would spray from the bottom of the foundation wall covering some of the plastic up to the subfloor and between the floor joists.
This is by far the best method to insulating a dry, above-grade crawlspace; however, this requires hiring 2 separate contractors that will probably try to talk a homeowner out of using the other contractor. The encapsulation company will want to just encapsulate the crawlspace and add foam board to the walls. This system will work just fine, but it isn't the most effecient. The foam contractor will want to just insulate the walls and throw down a vapor barrier, which still leaves the vents open to bring in cold air in the winter, and does not prevent all moisture from evaporating into the structure. A homeowner will have to be insistent on this exact process when speaking with both contractors.
As I said before, this process will only work in an already dry crawlspace which anymore seems like a rarity. If there are ANY signs of moisture at all, the insulating process will be completely different. Please refer to crawlspace insulating series for more information.
Check out this video on insulating a basement wall with spray foam.
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
Do not spray foam your crawlspace foundation walls
How to insulate crawlspaces - Encapsulate and Condition