spraying foam insulation in an attic
Q: I'd like to insulate my basement ceiling with a do-it-yourself polyurethane foam spray kit. Are they hard to use?
John Rudnicki, Lakeland, Tenn.

A: Tom Silva replies: Spray foam is great insulation, but it's fairly demanding to apply; the kit instructions have to be followed exactly. In fact, study them before you buy your kit so you know what you're in for.

Foam is very sticky; you'll need to wear disposable coveralls with a hood, and gloves, a face mask, and eye protection. It takes some practice to spray foam evenly and, because it expands so dramatically, to control its depth; 2 inches is all you need to seal the joist cavities. You need a clear area so that you can work without interruption; any pause longer than 30 seconds will clog the nozzle and require putting on a new one. It's also critical that the air temperature stays between 75 and 85 degrees.

Here's a simpler, less expensive alternative: Cut some 2-inch-thick rigid-foam insulation and glue it to the subfloor between the joists or support it with nails driven partway into the joists. Then fill any gaps between the edges of the foam boards and the joists using the canned spray foam sold at home centers or hardware stores. An even easier option is to nail the foam panels against the bottom edge of the joists and seal the joints with canned foam, but you'll lose some headroom and access to any pipes and wires between the joists. As with spray-foam kits, protect yourself and the floor from the dripping globs of canned foam. A full face shield, gloves, and a hat would be a good start.

Whichever insulation you choose, make sure that all of it is covered with a layer of ½-inch drywall to shield it from fire.

Shown: homeowners who want to spray their own foam should copy what the pros do and cover themselves completely before pulling the trigger.
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