Spray Foam Knowledge Quiz

Open-cell spray foam typically runs 0.45 to 0.90 per board foot, and closed-cell runs 1.00 to 2.50 per board foot installed. A board foot is one square foot at one inch thick, so thicker applications cost more.

Open versus closed cell, the thickness and R-value target, site access, prep work, whether the area is a roof deck or wall cavity, and removal of old insulation all affect the price. Closed-cell jobs cost more per inch and per square foot.

A typical attic runs 1,500 to 4,000 depending on square footage and the R-value target. Sealing the attic roofline rather than the floor changes the scope, so compare quotes on the same strategy.

Spray foam costs more upfront but seals air leaks, which is where most energy loss happens, and it lasts the life of the home without settling. Fiberglass is cheaper but does not air-seal and can sag or compress over time.

Closed-cell uses more chemical per inch, delivers about double the R-value per inch, and acts as its own vapor retarder and moisture barrier. Those properties justify roughly two to three times the per-board-foot cost.

Open-cell is cheaper, gives about R-3.5 per inch, and deadens sound, but it is vapor-permeable. Closed-cell gives R-6 to R-7 per inch, blocks moisture, and adds rigidity, making it the choice for roofs, basements, and wet areas.

Foam the roofline when ducts or equipment live in the attic, or for cathedral ceilings, creating a conditioned attic. Foam the floor when the attic is unconditioned storage, keeping the living space sealed below.

Yes. Closed-cell foam on below-grade walls resists moisture and insulates without fiberglass's mold risk. Just remember most codes require a thermal barrier such as drywall over the foam in living spaces.

Closed-cell foam becomes a vapor retarder once applied thick enough, typically 1.5 to 2 inches. Open-cell foam is vapor-permeable, so humid climates usually require a separate vapor retarder on the warm side of the assembly.

Small DIY kits work for rim joists, gaps, and small cavities, but they lay down thin coverage and cannot do a whole assembly properly. Professional application is required for full walls and roofs, and for any manufacturer warranty.

Look for a licensed, insured company with manufacturer-trained or certified applicators for the specific foam system they use. Ask to see training certificates and references from jobs at least one year old.

Ask about open versus closed cell, the target R-value and thickness, prep including removal of old insulation, temperature requirements for application, ventilation and re-entry time, and cleanup. Get the product name in writing.

A professional crew measures and documents the thickness in each area, and you can probe the cured foam to spot-check. If a building inspector is involved, they verify thickness and the required thermal barrier as part of the inspection.

Yes, in most jurisdictions, especially for additions, remodels, or roof assemblies. The building inspector checks foam thickness and that a thermal barrier covers the foam in occupied spaces.

That is fine, but confirm the crew doing your job is specifically trained and certified for spray foam application. Spray foam is chemistry-heavy, and crews that mostly install batts can misapply it.

Open-cell provides roughly R-3.5 to R-4 per inch, and closed-cell provides R-6 to R-7 per inch. Total R-value depends on thickness, so ask for the installed thickness, not just the R-number.

Most building codes require a 15-minute thermal barrier, typically half-inch drywall, over foam in living spaces, with intumescent coatings allowed in limited exposed areas. Skipping it fails inspection and is a fire hazard.

Most foams are low-VOC and cure within 24 to 72 hours, but the space must be ventilated during application and the installer's re-entry and reoccupancy schedule followed. Report any lingering strong odor to the installer immediately.

Expect a workmanship warranty from the installer plus a manufacturer warranty on the foam itself, and get both in writing. Ask what happens if adhesion or curing defects show up in the first year.

The components and surfaces need to be warm enough, often 50 to 60 degrees Fahrenheit or higher, for proper expansion and adhesion. Cold-weather spraying without conditioning can produce poorly cured, shrunken foam.

Thin application that misses the R-value target, poor prep leaving gaps at edges and penetrations, open-cell sold as closed-cell, no thermal barrier, and unvented roof assemblies without a proper moisture strategy are the classics.

Removal of old insulation, prep work, changes to roof ventilation, installing the required thermal barrier, and moving wiring or fixtures are common add-ons. Ask the contractor to scope the full assembly, not just the spraying.

Wrong mix ratios, low temperatures, moisture on the surfaces, or expired chemicals cause poor cure and odors. Professional rigs are calibrated and temperature-checked, which is why whole-home spraying is not a DIY job.

Closed-cell is expensive, and it is not always the right call: open-cell or a hybrid often meets the R-value target for walls and attics at lower cost. Let the R-value goal and moisture plan drive the choice, not the sales pitch.