How to Use a DIY Spray Foam Kit: Rim Joists, Sheds and Small Jobs
Updated · See the full spray foam insulation cost comparison
Foaming a 1,500 sq ft attic from kits yourself: $8,215–$8,495 in kits and gear, 14–24 hours — about what a pro charges.
- Kits pay off on rim joists, a shed or a few hundred board feet of gaps — jobs where a pro's minimum charge is the whole price. Above that, kits cost what a contractor charges.
- Full-face respirator with organic-vapor cartridges, coveralls, gloves. Everyone else out of the building until it's cured and aired, 24 hours minimum.
- Tanks at 75–85°F and a substrate above 50°F, or the foam comes out thin, crumbly and short. Warm the tanks indoors the day before.
- Spray in 1-inch passes and let each rise before the next. One thick pass overheats, shrinks and pulls away. Two inches of closed-cell on a rim joist is R-13 and a finished air seal.
Before you start
Read the cost comparison first if you’re deciding between a kit and a contractor. The short version: kits cost as much per board foot as a pro’s installed price, so they only pay where the pro’s minimum charge dominates — rim joists, a shed, a small outbuilding, gaps around a foundation. This guide is written for a rim joist at 2 inches of closed-cell foam. The steps are the same for a shed or small gap job. They aren’t for an attic or a garage; get quotes for those.
Two conditions before you commit: the surface is a clean, dry, framed cavity you can reach standing or kneeling, and you can send everyone else out of the building for a day.
What you need
For a 1,500 sq ft basement rim joist: a 200 board-foot closed-cell kit plus a small canister, or a 600 board-foot kit if you’re also doing a shed or gaps; a full-face respirator with organic-vapor cartridges; disposable coveralls, nitrile gloves and goggles; plastic sheeting, tape and acetone; a fan, work lights and a handsaw. Priced list on the cost page. Kits include the gun, hoses and tips.
The two things that decide how it turns out
Temperature. Cold tanks or a cold wall produce off-ratio foam that’s dense, dark and short. Everything else in this job is forgiving; this isn’t. Warm the tanks overnight and don’t spray on a surface below 50°F.
Respirator discipline. The rim joist is a confined space and isocyanate vapor is invisible. Full-face respirator with organic-vapor cartridges, on before the valves open, off only after you’ve left the space. Sensitization from one bad exposure is permanent.
Step by step
-
Size the job and buy the kit
Measure the area in square feet and multiply by the depth in inches for board feet: a rim joist is the linear feet around the basement times the joist depth in feet (10 inches is 0.83 ft), so 150 ft × 0.83 × 2 in = about 250 board feet. Buy a kit at least 20% bigger than that — 70–85% of rated yield is what you'll get. Buy the respirator, cartridges, coveralls and gloves at the same time.
-
Prep the surface
Foam only sticks to clean, dry, dust-free surfaces. Vacuum the rim joist cavities, pull out old fiberglass, and scrape loose paint or debris. Fix any water leak first — foam over a wet rim joist traps moisture against the wood. Fill gaps wider than 1/2 inch with backer rod or canned foam so the kit foam has something to bridge.
-
Mask everything
Plastic and tape over the floor beneath the work, wiring you don't want buried, pipes, windows, the water heater and furnace, and anything within 10 feet. Overspray is a fine mist that travels. Clear a path to the exit and open a window with a fan pulling air out — not blowing in.
-
Warm the tanks and get dressed
The tanks should read 75–85°F: keep them in a heated room overnight, or on a heating blanket. Shake each tank for a minute. Suit up completely — coveralls with the hood up, gloves taped, full-face respirator with fresh organic-vapor cartridges — before opening a valve. Everyone else leaves the building now.
-
Connect and test-spray
Attach the hoses, open both tank valves fully, and fit a tip to the gun. Spray a 10-second test onto a piece of cardboard: good foam is a light, even color and rises to about 3 times its sprayed thickness within a minute. Dark, glassy, crumbly or slow-rising foam means one tank is cold or a hose is kinked — stop and fix it. Never spray on the work until the test looks right.
-
Spray in 1-inch passes
Hold the gun 18–24 inches from the surface and move steadily, laying down about an inch. Work into the corners of each cavity first, then the field. Let each pass rise and skin (2–5 minutes) before the next. Build to 2 inches for a rim joist or unconditioned space, 3 for a heated one. Keep the gun moving between cavities; if you stop for more than 30 seconds, change the tip — a clogged tip sprays off-ratio.
-
Finish and let it cure
Once the depth is right, close the tank valves, trigger the gun to relieve the hose, and leave the space with the fan running. The foam is tack-free in minutes and cured in about an hour, but keep everyone out for at least 24 hours while it off-gasses. Trim any foam that stands proud of the framing with a handsaw once it's hard.
-
Clean up and dispose
Wipe any wet overspray with acetone right away. Remove the masking carefully — cured foam on the plastic pulls off cleanly. Bleed the tanks fully before disposal: open the valves outdoors with the gun disconnected until they stop hissing, then check local rules — some areas take empty tanks as scrap steel, others want them at a hazardous-waste day. Cartridges go in the trash; gloves and coveralls too.
What would this cost you? The spray foam insulation calculator prices the DIY version with the tools you already own and a value on your time, next to a pro quote.
Frequently asked questions
How many board feet is a spray foam kit?
Kits are sold by rated yield: 200 board feet (a rim joist or a shed) for about $400, and 600 board feet for $700–$1,000. A board foot is one square foot at one inch deep, so a 600 board-foot kit covers 300 square feet at 2 inches. Rated yield assumes perfect conditions; plan on 70–85% of it. A 1,500 sq ft basement rim joist — about 150 linear feet by 10 inches — needs about 250 board feet at 2 inches, which is a 200 kit plus a small canister, or most of a 600.
What safety equipment do I need for DIY spray foam?
A full-face respirator fitted with organic-vapor cartridges (a P100 dust mask is not enough — isocyanate vapor passes straight through), disposable coveralls with a hood, nitrile gloves taped at the cuff, and safety goggles if the respirator is a half-mask. Ventilate with a fan pulling air out of the space, and keep everyone else, including pets, out of the building until the foam has cured and the space has aired for at least 24 hours. Isocyanate sensitization is permanent.
What temperature does spray foam need?
Tanks at 75–85°F, the surface you're spraying above 50°F (60°F is better), and air that isn't humid enough to leave the surface damp. Cold tanks are the most common DIY failure: the two parts don't mix at the right ratio, and the foam comes out dark, dense, crumbly or off-ratio. Bring the tanks inside for a day before the job, or wrap them in a heating blanket, and never spray on a cold basement wall in winter without warming it first.
How thick should each pass of spray foam be?
About one inch, then let it rise and skin for a few minutes before the next pass. Closed-cell foam generates heat as it cures; a single 3-inch pass can overheat, scorch, shrink and pull away from the framing — or in bad cases smolder. Build to depth in layers. Two inches of closed-cell is R-13 to R-14 and is the standard rim joist depth; go to 3 inches for a heated shop.
Can I spray foam my attic myself?
You can, but the math is against it: a 1,500 sq ft attic roof deck is 5,000–10,000 board feet, which is 9–15 kits at $700–$1,000 each, before the ignition-barrier coating code requires over exposed attic foam. That's $8,215–$8,495 against a typical $7,500 professional quote, done lying on your back in a hot attic with a fogged respirator. Kits are for rim joists, sheds, small outbuildings and gaps.
How do I clean up spray foam overspray?
You mostly don't — cured foam bonds permanently. Wipe wet foam immediately with acetone or the kit's cleaner; once cured it can only be cut or scraped off, which damages most surfaces. Mask everything you don't want foamed with plastic and tape before you start, including windows, wiring, the floor, and anything within 10 feet downwind. Trim proud foam flush with a handsaw or a serrated knife after it cures.
Sources
- Insulation Workers, Floor, Ceiling, and Wall (SOC 47-2131), Occupational Employment and Wage Statistics , U.S. Bureau of Labor Statistics, 2026-04
- How Much Does Spray Foam Insulation Cost? , HomeGuide, 2026-09
- How Much Does a DIY Spray Foam Insulation Kit Cost? , HomeGuide, 2026-09
- How Much Does Spray Foam Insulation Cost? , Angi, 2026-09
- Types of Insulation , U.S. Department of Energy, 2026-09
- Quick Safety Tips for Spray Polyurethane Foam Users , U.S. Environmental Protection Agency, 2026-09
- International Residential Code, Section R316: Foam Plastic , International Code Council, 2026-09
Figures last reviewed . See how we estimate.