Choosing the Right Spray Foam Insulation for Your Home Improvement Project

spray foam insulation

You need your money more than the electric utility company does. That’s the point of having a well-insulated house: It keeps you comfortable, no matter what the weather or season, while saving more of your heating and cooling dollars. Spray foam insulation does the job better than other choices.

Understanding the different spray foam formulas, application methods and practical uses is critical to a successful installation.

Long ago, houses were poorly insulated (if at all), first with sawdust and later with vermiculite, little absorbent pebbles that resembled kitty litter and sometimes, when wet, acted like it too. Modern building technology delivered cellulose, Styrofoam and fiberglass batts — reliable performers when used in the right applications. But the newcomer on the block, spray foam insulation, has better insulating power, resists mold and insects and also works in areas where other insulation doesn’t.

Understanding the different spray foam formulas, application methods and practical uses is critical to a successful installation.

Open-Cell vs. Closed Cell Spray Foam Insulation

Each spray foam insulation product, no matter how it is applied, falls into either the open-cell or closed-cell category. Spray foam insulation in an aerosol can is typically closed-cell, but both low-pressure and high-pressure sprayers apply both types interchangeably.

So what’s the difference? Sure, both look much the same, insulate well and eliminate the need for a separate vapor barrier. But closed-cell is more rigid, exceptionally dense and offers a higher R-value, at 6.6, than open-cell spray foam insulation does at 3.9. Incidentally, open-cell is comparable to other insulation products while closed-cell insulates about twice as well. This means it takes twice as much open-cell insulation to achieve the same R-value as the closed-cell.

Closed-cell expands a little more slowly and creates a better moisture and air barrier than open-cell. Open-cell, in contrast, expands and cures quickly, causing the tiny cells to expand so fast that they break and fill with air, which results in a soft, slightly spongy insulation that is more moisture-permeable than closed-cell.

Location is Everything

A slow-curing formula of open-cell spray foam insulation is favored when retrofitting wall insulation. An installer makes small holes in the drywall and inserts a sprayer nozzle, which fills the cavity with a liquid that expands, like hair mousse or shaving cream, inside the wall. Using other formulas may cause your wall to bulge under the pressure and even burst.

In new construction, open-cell is often chosen for ceilings, interior walls – it soundproofs twice as well as closed-cell – and most anywhere you would use cellulose or fiberglass. Closed-cell should be used wherever moisture will be a problem, but either closed-cell or open-cell can be used in other, drier applications.

Spray Foam Equipment: Professional vs. DIY Installation

High-pressure sprayers attached to large drums of two-part foam formulas cover a lot of area quickly and are useful for larger jobs such as roofs or major renovations. Professional applicators bring a spray rig on a commercial truck to the house. Long hoses are threaded around and into the house where the installers, who wear protective gear, spray the insulation. This is not a DIY job. Not only is the equipment expensive, but specialized training is required.

With the proper protective wear, which includes eye goggles and a respirator along with long pants and sleeves, an ambitious do-it-yourselfer can wield a low-pressure sprayer hooked to portable tanks of two-part foam insulation formulas.

Smaller projects, such as crawl spaces and attics, are suitable for low-pressure sprayers. With the proper protective wear, which includes eye goggles and a respirator along with long pants and sleeves, an ambitious do-it-yourselfer can wield a low-pressure sprayer hooked to portable tanks of two-part foam insulation formulas. This generally isn’t something you can rent; disposable and refillable tanks are sold as part of a spray foam insulation kit; the cost is steep. In addition, using the sprayer successfully can prove tricky. Most experts recommend leaving low-pressure sprayers to the professionals, so proceed with a DIY installation only after you thoroughly read the instructions enclosed in the kit. Sprayer operation and other specifications will vary slightly by manufacturer.

Designed to fill smaller cracks, gaps and holes around the house, canned spray foam can be found at most general department stores and home improvement centers. Looking much like a bottle of canned air or lubricant, the one-part closed-cell spray foam has an attached nozzle that makes pointing, inserting and spraying easy. Although foam from a can won’t go very far, it's the perfect choice for homeowners who need to fill a few small insulation gaps.

Preparing for Spray Foam Insulation

Whether you are spraying a low-pressure foam insulation or using spray foam in a can, establish a plan of action before you begin. Examine the house envelope – the skin of the house, if you will, where heat meets cold – and identify areas where you see daylight, feel a draft or find an obvious lack of insulation. Make a list so you know exactly where to go, step-by-step, as the foam can very quickly clog the nozzle of a sprayer or can.

Open a window or turn on a fan to provide ventilation while you work, and have children and pets leave the area.

Clean debris from surfaces and sink or remove nails you encounter. Unlike painting or staining, detailed cleaning isn’t necessary, but it’s smart to remove or eliminate anything that will keep the insulation from bonding completely.

Before beginning, cover floors or nearby furniture and other items with plastic sheeting to protect them from excess spray. Cut scraps of plastic and tape in place over electrical outlets and light switches to prevent foam from invading the receptacle. Turn off any sources of flame near the installation area, as the foam is extremely flammable during installation. Open a window or turn on a fan to provide ventilation while you work, and have children and pets leave the area.

DIY: Spray Foam in a Can

Shake the can for about a minute to thoroughly mix the contents. Assemble the bottle, attaching the straw applicator or nozzle to the can top. Working quickly, stick the applicator into a gap or hole and squirt to fill about halfway. The foam insulation will swell instantly. Move on to the next spot, adding more foam to previous areas, if they need it, only after waiting 10 to 15 minutes or until the first layer is dry. Spray a little water over top before adding more insulation.

If the hole is overfilled, feel free to trim away the excess with a utility knife or other tool. This allows you to hang sheathing, trim or any material you desire without a bulging surface underneath. Cure the foam insulation overnight before altering. It will shave easier when hard.

As with any method of application, take care to avoid overfilling holes, especially around items such as windows and doors. Overzealous and inexperienced applicators may damage window and door frames or even break things if too much insulation exerts excess pressure.

Where to Apply Canned Spray Foam Insulation

As tedious and expensive as it would be, you could insulate with a can of spray foam insulation anywhere you would use a sprayer. However, due to the small amount in each can, it wouldn’t be practical. Some areas, in particular, are prime candidates for your attention with canned foam:

  • Seal gaps around windows and doors. Pull trim off to access space around the jambs that the builder may not have insulated properly. Take care to avoid overfilling these areas.
  • Add foam around wire and pipe entry spots, vents or other intrusions through the exterior walls. Spray foam does not harm wiring.
  • Insulate around plumbing in the bathroom and kitchen.
  • Squirt insulation around dryer vents, working from either inside or outside the house.
  • Inspect the sill plate in the basement. Where the wood framing meets a foundation there may be a gap. Fill areas such as these with insulation.
  • Seal around penetrations, such as around registers and HVAC vents, from the attic to the ceiling.
  • Run a bead around the attic trap door and along the eaves in the attic.
  • Add insulation where the siding meets the foundation on the house exterior. Leaving exposed foam on the exterior doesn’t harm anything.
  • Surround any electrical, water, gas or HVAC inlets and outlets. Even the smallest hole allows insects, pests and moisture or air entry to your home.
  • Insulate around outdoor faucets and exhaust fan outlets.

Hardcore DIY: Spray Foam with Low-Pressure Sprayers

If you’re taking a leap of faith and attempting a low-pressure installation on your own, assemble the sprayers as directed. From a distance of about two feet away, aim the sprayer nozzle at the wall and spray in an even sweep across the surface. Practice a few times to get the feel; spraying foam insulation is like spray-painting a car or other item. You need a light, steady fan of insulation applied with a swing of your arm.

For best results, check the temperature of both the ingredients and the environment before spraying foam insulation. Apply when temperatures range between 60 and 80 degrees Fahrenheit.

Use a back-and-forth technique to spread a thin but even coat of less than an inch in depth. Continue down the wall, ceiling or other surface, steadily applying more in a zigzag pattern. Any time you stop for longer than 30 seconds, you must change the sprayer nozzle or you risk clogging the machine, which may force you to purchase another one.

After two or three minutes, the foam will have reached full inflation depth of about an inch. Remembering your R-values – 3.9 for open-cell and 6.6 for closed cell – add another sweep to increase your R-values and energy efficiency. Each inch in depth will deliver the R-value stated, so multiple layers offer doubled or tripled values.

Avoid spraying a thick layer in one sweep to prevent it from simply falling off the surface. For best results, check the temperature of both the ingredients and the environment before spraying foam insulation. Apply when temperatures range between 60 and 80 degrees Fahrenheit.

Aftercare for Spray Foam Insulation

Don’t simply paint over foam and treat it as a finished surface inside your home. Like any foam insulation, expanding foam ignites quickly and easily and the fumes it emits are toxic. Building code generally insists that interior applications are covered with a fire-resistant sheathing. Drywall works exceptionally well, as it resists burning for about 15 minutes. In addition, do not spray foam with chemicals such as gasoline or expose it to extremely high temperatures or heat sources to prevent chemical reactions or combustion. Consult your local building code for further information about building safety requirements in your area.