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insulation, walls

When to use spray foam insulation

From open cell and closed cell to soy and DIY kits, here’s everything you need to know about insulating with spray foam.
by Rhea Seymour

How does spray foam work?

Polyurethane foam is sprayed directly onto wall and floor cavities as a liquid and quickly transforms into thick, hard foam insulation. There are two categories of foam: half-pound open-cell foam and higher density two-pound closed-cell foam, which acts as a unique air and moisture barrier in one. “Half-pound has certain uses like insulating interior walls, and it’s better than fibreglass batts, but it doesn’t compare to two-pound closed-cell, which does a better job of making a home airtight than other types of insulation,” says Andrew Cole, chair of the Canadian Urethane Foam Contractors Association in Winnipeg. It’s also resistant to mould growth, unlike fibreglass and cellulose, which can trap unwanted moisture and organic material.

What are the benefits of insulating with spray foam?

Highest R-value
Closed-cell foam is the highest-R-value insulation material available, at up to R6 per inch (the higher the R value of a material, the greater its resistance to the movement of heat). “Using thermal imaging cameras with a blower door, it’s not uncommon to see missing pieces of fibreglass or a two-inch gap between batts where heat can be lost,” says Gwendal Castellan, an independent certified energy advisor who works with City Green Solutions in Vancouver. “With well-installed foam that’s less likely to happen because it’s sprayed on.”

Space savings
Spray foam takes up much less space than fibreglass or blown-in cellulose. Its thickness depends on where it’s applied, but it averages about three inches deep once installed.

Energy savings
With an energy-efficient furnace, you can see savings of up to 40 percent or more if your house is reinsulated with spray foam.

Are there any drawbacks?

Not all green
Well-insulated homes are eco-friendly, but the insulation itself isn’t. Polyurethane spray foam products may contain soy, vegetable oil or recycled bottles but they are primarily made of oil or petroleum.

Since UV light degrades the foam, it always needs to be covered. To retrofit, plan to remove and replace drywall.

What room is right for spray foam?

All foams are flammable and require an ignition barrier if installed near a flame source, such as a furnace or water tank. Otherwise, closed-cell spray foam can be used anywhere. It’s especially effective in attics and the rim joist cavities in basements, where the floorboards rest on the foundation. “Existing attics have a high failure rate because warm air enters the attic and moisture mats down the fibreglass and reduces its R value from 40 to about 12,” says Cole. “Adding fibreglass atop a two-inch barrier of closed-cell foam will operate at R50.”

Is spray foam suitable as a DIY project?

Spray foam off-gasses during installation so installers wear protective gear. “Homeowners are not adequately trained and shouldn’t be inhaling the isocyanates in spray foam or getting them on their skin,” says Cole. According to the U.S. Environmental Protection Agency, exposure to isocyanates and other spray-foam chemicals during installation may cause adverse health effects like asthma.

Spray foam is also messy. “You’d have to be very handy to do it yourself,” says Castellan. “With closed-cell foam, there’s a risk of fire if you spray it up too thickly too soon so if you’re going to get a DIY kit, be aware of the challenges. Make sure to read the specifications and instructions carefully. Hopefully the vendor is able to offer training support as well.”

What does it cost?

Closed-cell spray foam is the most expensive insulation choice, says Cole, at about $3-$3.50/sq. ft. (with thickness of three inches) for walls and $4-$5/sq. ft. to replace fibreglass with foam in an attic (it’s pricier because the product is a combo of closed-cell and cellulose insulation). On the upside, it can be installed faster than other insulations and it lasts a lifetime. “We estimate the payback period is five to seven years,” says Cole. A DIY kit that covers 200 sq. ft (with thickness of one inch) with a hose-and-gun assembly costs about $465.

You might be eligible for government rebates on insulation. Find out how much with our Rebates Finder.

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