"We are building a new home near the Oregon coast on a particularly windy site. My contractor tells me we should use spray-foam insulation. What is that and is he right?"
Answer from Ross Sanders
Your contractor is definitely on to something here. Sprayed insulation has been around for a while, but in recent years, it has been increasingly used in highly energy efficient houses.
In traditional "stick-framed" construction, fiberglass batting insulation strips are stapled in between the wood studs to insulate exterior walls. These battings are sized to fit between the studs (typically 16" or 24" on center depending on the stud depth), but they tend to leave air gaps at the edges, top and bottom. To reduce air flow through these gaps and through the batting themselves, a separate vapor barrier is added to the interior of the wall assembly before the interior finish is added. Unfortunately, this vapor barrier is often damaged, incomplete, and penetrated by things like wall switches, outlets, and plumbing.
Sprayed insulation, usually a two-part foam mixture sprayed by a large paint-gun, acts to a large degree as its own vapor barrier. The expanding foam fills the study cavity and seals small gaps, then expands outward to completely fill the void. Any insulation bulging out beyond the wood studs is then trimmed off to create a smooth surface for the interior finishes. The insulation value of sprayed products vary by manufacturer, but can provide very good thermal protection for your home. As you might guess, sprayed insulation is typically more expensive than batting, but it can create a warmer, drier interior environment which will save you money in the long run. Note that there are hybrid systems which use a 2" sprayed insulation layer to seal the outside of the stud cavities with traditional batting insulation added to fill the remainder of the cavity. This hybrid approach has priced favorably on projects in my experience, so it may be worth mentioning to your contractor.
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