Is spray foam insulation worth it?

Short answer: Sometimes. Spray foam is an excellent air barrier, but the DOE lists it as expensive [1]. It earns its cost on rim joists, block walls, roof decks, pole barns and metal buildings. For a typical vented attic floor, blown in fiberglass or cellulose is usually the better value.

Where foam earns it

The DOE rates sprayed foam an excellent air barrier that can eliminate the need for separate air-tightness detailing, and lists its best uses: the perimeter of vented attics, roof decks of cathedralized attics, vaulted ceilings, flat roofs, basement walls, and walls with siding removed [1]. On rim joists the DOE says the best moisture control comes from filling the joist cavities with spray foam [1].

Where it usually does not

An open, vented attic floor with room for 14 or more inches of blown insulation. There, blown fiberglass or cellulose gets you to R-49 or R-60 for far less. ENERGY STAR also rates spray foam an advanced job that needs a certified installer [2], and the DOE notes foam installation calls for protective equipment and ventilation [3].

Closed cell or open cell

Closed cell is about R-6 per inch and more costly; open cell is vapor-permeable, lower R-value and less expensive [4]. Around here we usually recommend closed cell. The full comparison, with the DOE's table, is on our insulation questions page.

Our spray foam work.

More questions

Is closed cell better than open cell?

Closed cell is about R-6 per inch, a vapor retarder and more costly; open cell is vapor-permeable, lower R-value and less expensive. For most jobs in Ohio we recommend closed cell.