Spray Foam Insulation in Boston, MA

Spray foam insulation is a polyurethane product that is mixed at the gun, expands as it lands and bonds to wood, brick and stone. Its big advantage over batts and loose fill is that it stops air as well as heat. In older Boston houses, air leaks cause most of the discomfort: cold air pulled in at the sill, warm air escaping at the top plates and roof. Foam is the most direct way to close those gaps where loose fill cannot.

Open-cell

Open-cell foam is light, about half a pound per cubic foot, and expands a lot. It fills irregular cavities, stops air and dampens sound, at R-3.5 to R-3.7 per inch according to HomeGuide. It allows some water vapor through, so in Climate Zone 5A it is used where the vapor side is handled another way, or between heated floors. It costs less per square foot than closed-cell.

Closed-cell

Closed-cell foam is dense, at R-5 to R-7 per inch. At typical thickness it is a vapor retarder and does not absorb water, and it adds stiffness to the surface. That makes it our usual choice for rim joists, brick and fieldstone foundation walls, the underside of low-slope triple-decker roofs, floors over open porches and anywhere space is tight. It costs more, so we use it where those properties matter.

Where foam is not the answer

On an open attic floor, the cheapest way toward the R-60 listed in the Massachusetts stretch code summary is to seal the gaps and blow loose fill. In closed plaster walls, dense-pack cellulose is usually more practical. We will tell you when foam is not the best buy for a space.

Typical Boston foam jobs

Rim joists around the basement of a two-family. The rafters of a finished third-floor room in a Victorian. The ceiling of a top-floor triple-decker unit under a flat roof, when the cavity is too shallow for loose fill. The floor of a room built over an old porch. Exposed stud walls during a kitchen or bath gut renovation. Each of those is a case where foam's air sealing and R-value per inch make the difference.