Crawl Space Spray Foam Insulation

Many older homes around Dallas–Fort Worth sit on pier-and-beam foundations, with an open, vented crawl space under the floor. Outside air moves through it all year. In winter the floors run cold and drafts come up around pipes, ducts and floor registers. In summer, humid air hangs under the house. Closed cell foam sprayed on the underside of the subfloor and the rim joists seals the floor from below and insulates it in one step.

Why closed cell under a house

A crawl space is damp. Open cell foam and fiberglass batts can hold moisture, and batts under a floor often end up sagging or on the ground. Closed cell bonds to the wood, doesn’t absorb water, and at about 1.5″ and thicker it acts as a vapor retarder, so ground moisture doesn’t move up into the floor. At 2″ it gives about R-13.

What we spray

• The underside of the subfloor, between the joists, so the floor is sealed and insulated.
• The rim joists around the edge of the house, where most of the air leaks in.
• Around pipes, wires and duct boots that go through the floor.

We keep plumbing cleanouts, shutoff valves and the access opening clear.

Before we spray

The crawl space has to be dry. On the measure we look for plumbing leaks, standing water, poor drainage around the house and wood damage. Those need to be fixed before foam goes in, because foam shouldn’t cover a moisture problem. We also need room to crawl and spray. Old batts hanging from the joists come out first; see insulation removal.

If your home has a termite treatment contract, ask your pest company whether they want an inspection strip left clear along the top of the foundation. We can leave one.

Ductwork under the floor

Some older homes have heating and cooling ducts in the crawl space. Sealing the floor above them helps the rooms, but the ducts still sit in outside air. In those homes we may recommend a different approach, such as sealing and insulating the crawl space walls instead of the floor, and we will explain the options on the measure.

Ignition barrier

Foam left exposed in a crawl space that is entered only for service usually needs an ignition barrier. Some foams are tested to go without one in crawl spaces; others need a coating. Your quote lists what applies.

Crawl space questions

Will crawl space foam keep my pipes from freezing?

It helps, because the floor and the space right under it stay warmer, but it is not a guarantee. Pipes that run through open crawl space air can still freeze in a hard freeze. Insulating the pipes themselves and closing the foundation vents during a freeze protect them better.

Why not just put fiberglass batts between the floor joists?

Batts don’t stop air, they hold moisture in a damp crawl space, and they tend to fall down over time. Closed cell foam seals the floor, stays put and resists moisture. It costs more than batts, but it does the job batts are supposed to do.

How much room do you need under the house?

Enough for an installer to crawl and reach the underside of the floor with a spray gun. Very low spots, or areas blocked by ducts and pipes, may have to be done differently. We check clearances on the free measure.

Can you insulate the crawl space walls instead of the floor?

Yes. For a sealed crawl space, foam goes on the perimeter walls and rim joists, a heavy vapor barrier goes on the ground, and the vents are closed. That approach makes sense when ducts or plumbing run through the crawl space, but it changes how the space is ventilated, so we plan it with you and your HVAC contractor.