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Best Way to Insulate Crawl Space with Spray Foam: Walls or Ceiling?

Creating an air seal in your crawl space is a great idea in the process of creating a comfortable home, but is spraying foam on the walls or ceiling more efficient? There are reasons why one crawl space spray foam installation might be favored over the other, and that comes down to what is in the space. It all comes down to where the mechanicals in your home are located.

First and foremost, when adding spray foam insulation to your crawl space all of the old insulation needs to be removed first. It doesn’t matter if the ceiling or the walls are being sprayed, that old stuff has to go. It’s dirty, nasty, probably wet, and really, it’s just in the way. A good contractor will get that old insulation out of your crawl space, so the spray foam has a nice clean surface to adhere to. It just comes down to whether the ceiling or the walls will be sprayed, and that decision is made based on whether there are mechanicals or ductwork in your crawl space.

Insulating the Crawl Space Walls with Spray Foam

If there is any ductwork or mechanicals running through the crawl space, then a good contractor will recommend laying plastic down on the ground and spraying the walls. Once the old insulation has been removed from the crawl space, the installation crew will run a hose down into the crawl space as part of the preparation for installation. The crew then will lay a layer of plastic on the crawl space floor and up the walls. They will then apply the spray foam to the walls.  This method seals off the foundation of the home and allows the crawl space to be the same temperature as the rest of your home. You want this because the cold air coming into the crawl space can actually cool down those ducts, thus making your furnace work overtime. The rim joist is also included in this installation.

Insulating the Crawl Space Ceiling with Spray Foam

If there aren’t any mechanicals or ductwork in your crawl space, then your insulation contractor may recommend insulating the ceiling. The preparation for this method is similar to spraying the crawl space walls, except no plastic is used. Again, the old insulation will be removed and a hose will be run down into the crawl space. Next, the installation crew will spray the foam on the underside of your floor. This method will air seal the crawl space separating it from the rest of the home. The crawl space will then be outside of the building envelope, which means it won’t be the same temperature as the rest of your home but also will no longer allow cold air to move through it and into your living space.

The Building Science Corporation recommends spray foam for the crawl space no matter which installation method is used. This is because the insulation material creates an air barrier that will work to make your home more energy efficient and comfortable.

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