Closed Cell Spray Foam, Explained for Colorado Homes
Closed cell spray foam is a rigid, high density insulation that goes on as a liquid and cures into an air barrier, a vapor retarder, and an insulation layer at once. This guide is for Greeley and Weld County homeowners deciding whether it belongs in their crawl space, attic, or pole barn, and what it costs.
What is closed cell spray foam, exactly?
Closed cell spray foam is a two part polyurethane product. An installer mixes the two chemical sides at a heated spray gun, and the mixture expands on contact with the surface, then hardens within seconds.
The name describes the structure. Each tiny gas bubble in the cured foam is a sealed cell with walls that neighboring cells do not share openings with. Nothing moves through easily: not air, not water vapor, not heat.
That closed structure is why the material is rigid enough to knock on. Closed cell spray foam delivers R-6.5 to R-7 per inch, the highest R-value per inch of any insulation a residential crew installs on a normal job.
How is closed cell different from open cell spray foam?
Both products are sprayed polyurethane, and both seal air leaks. Everything else about them differs, because open cell foam's bubbles are broken open. That makes it soft, light, cheap, and permeable to water vapor.
The short version: closed cell buys performance per inch and moisture control, open cell buys volume per dollar. A cathedral ceiling with a three inch cavity needs closed cell. A wide open attic floor with room for sixteen inches of material does not.
| Property | Closed cell | Open cell |
|---|---|---|
| R-value per inch | R-6.5 to R-7 | R-3.5 to R-3.7 |
| Vapor behavior | Vapor retarder at about 2 in | Vapor open, needs a separate plan |
| Density | Rigid, roughly 2 lb per cubic foot | Soft, roughly 0.5 lb per cubic foot |
| Adds rack strength | Yes, bonds to the framing | No |
| Water resistance | Does not soak up bulk water | Absorbs and holds water |
| Installed cost | $1.00 to $1.50 per board foot | $0.45 to $0.75 per board foot |
If you are weighing the two for a specific project, the closed cell service page walks through assembly by assembly, and the spray foam cost calculator puts a range on your square footage in about ten seconds.
Want to know which foam your crawl space actually needs? Call (970) 414-2650
Where does closed cell foam earn its price in Weld County?
Four spots come up over and over on jobs around Greeley, Evans, and the county's farm roads.
- Crawl spaces. Ground moisture and cold air both come from below. Closed cell handles both in one pass, which is why sealed crawl space work almost always specifies it.
- Rim joists. The band of framing where the floor meets the foundation is the single leakiest strip in most pre-1980 Greeley houses. Two inches of closed cell shuts it down.
- Metal buildings and pole barns. Condensation drips off cold steel all winter. Foam bonded to the panel keeps warm indoor air from ever reaching that cold surface.
- Vaulted or cathedral roof decks. When there is no room to stack depth, R-value per inch is the only lever you have.
Chinook winds matter here too. A warm downslope wind can push forty miles an hour across the Front Range and drive air straight through a leaky band joist. Foam that seals and insulates in the same step is a real answer to that, which is why it pairs so well with air sealing work in the attic.
What does closed cell spray foam cost?
Installed pricing runs $1.00 to $1.50 per board foot in Northern Colorado. A board foot is one square foot at one inch of depth, so two inches over 1,000 square feet is 2,000 board feet.
That math puts a typical two inch crawl space wall job at a few thousand dollars, and a full three inch roof deck considerably higher. Per square foot of surface, most closed cell work lands between $2.00 and $4.50 depending on depth.
Full ranges by project type, including open cell comparisons and removal add ons, live in the Greeley spray foam cost guide.
When is closed cell the wrong choice?
Three situations. First, an open attic floor with unlimited depth, where blown-in cellulose or fiberglass reaches R-49 to R-60 for a fraction of the price. Second, a house with an active roof leak or plumbing leak, because foam over wet framing traps the water instead of fixing it.
Third, any assembly a code official or building scientist says needs to dry toward the inside. Foam is permanent. Getting the assembly right before the hose comes out matters more than the product choice itself.
For a broader look at the concerns people raise online, read why spray foam is sometimes called a red flag.
Common questions about closed cell spray foam
Is closed cell spray foam worth the extra money?
In a crawl space, a rim joist, a metal building, or anywhere moisture is part of the problem, yes. Closed cell delivers roughly twice the R-value per inch of open cell and stops water vapor at the same time. In a vented attic with plenty of depth to fill, cheaper blown-in material usually buys more R-value per dollar.
Does closed cell spray foam need a separate vapor barrier?
At about two inches of thickness and up, closed cell foam is its own vapor retarder, which is why crews use it against crawl space walls and rim joists. Always confirm the thickness with the installer and with the Weld County building department for your specific assembly.
How thick should closed cell spray foam be?
Two inches gets you roughly R-13 to R-14 and vapor control. Three inches lands near R-20. Attic roof decks in climate zone 5B often need more than that, so the depth is set by the R-value target, not by habit.
R-value guidance referenced from the U.S. Department of Energy's insulation material comparison: energy.gov.
Get a real number for your foam project
Tell us the room, the square footage, and what it is doing wrong. You get a straight price range on the phone and a firm quote after we look at it.
Call (970) 414-2650Greeley, Evans, Windsor, Eaton, Johnstown, Milliken, Severance, and Weld County.