SPRAY FOAM VS. RIGID BOARD INSULATION FOR OHIO CRAWL SPACES

If you've had your crawl space inspected and found wet, sagging fiberglass insulation hanging from the floor joists, you already know it needs to go. Fiberglass batt insulation was never meant for the damp, unconditioned environment of a crawl space. Once it gets wet — and in Ohio, it always gets wet — it loses its R-value, traps moisture against the wood, and becomes a mold habitat.

After removing the failed fiberglass, the two main options for crawl space wall insulation are closed-cell spray foam and rigid foam board. Both work. The right choice depends on your foundation type, budget, and the condition of your crawl space walls.

CLOSED-CELL SPRAY FOAM

Closed-cell spray polyurethane foam delivers roughly R-6.5 per inch of thickness. At two inches, you're at R-13 — well above the R-10 minimum recommended for Ohio's Climate Zone 5. But the R-value is only part of the story.

Closed-cell foam also functions as an air barrier and a vapor retarder. It adheres directly to the foundation wall, sealing cracks, gaps around rim joists, and irregular surfaces that rigid board can't fully contact. For older Twinsburg homes with fieldstone or rubble-stone foundations — common in pre-1940 construction — spray foam is often the only insulation that can conform to those uneven surfaces.

The tradeoff is cost. Professionally installed closed-cell spray foam runs approximately $2 to $3 per square foot, depending on thickness and accessibility. It also requires specialized equipment and must be applied by trained installers to ensure proper expansion and adhesion.

RIGID FOAM BOARD (XPS AND POLYISO)

Rigid foam board insulation — typically extruded polystyrene (XPS) or polyisocyanurate (polyiso) — delivers approximately R-5 per inch. Two-inch panels provide R-10, which meets the Zone 5 minimum. The panels are cut to fit, mechanically fastened or adhered to the foundation wall, and all seams are sealed with foam-compatible tape or caulk.

Rigid board is less expensive than spray foam — typically $1.50 to $2.50 per square foot installed. It works extremely well on flat, regular foundation walls: poured concrete and concrete block foundations that are in good condition and relatively plumb. The installation is also less specialized, which can translate to faster project completion.

The limitation is coverage on irregular surfaces. Rigid board leaves gaps on bowed walls, around protruding stones, or at rim joist intersections where the fit isn't flush. Those gaps allow air movement behind the insulation, reducing its effective performance.

WHICH ONE FOR YOUR TWINSBURG HOME?

In our Twinsburg projects, the wall condition drives the recommendation. For older homes with fieldstone foundations, irregular block, or significant wall bowing, we use closed-cell spray foam because it's the only option that makes full contact with the surface. For newer construction from the 1970s onward with flat block or poured concrete walls in good condition, rigid board delivers excellent performance at a lower price point.

Both options perform well when combined with full encapsulation and dehumidification. Insulating the walls without controlling the moisture in the crawl space is like insulating a shower — the insulation only works as part of the complete system.

Not sure which option fits your home? We assess the wall condition during our free crawl space inspection and recommend the insulation type that makes sense for your specific foundation.