Spray foam insulation: what to know

What the job involves, what changes the price, and what to ask a pro.

What spray foam insulation is

Spray foam insulation applies foam that expands to seal gaps and insulate attics, walls or crawl spaces. It is a specialized job because the foam chemicals must be mixed and applied at the right temperature by trained applicators, with protective gear and ventilation while it cures.

Signs you need it

  • There are large air leaks at the rim joists, the attic top plates or the crawl space walls, and the house drafts badly.
  • The crawl space is damp or cold, and you want to insulate and air seal the walls and the floor above.
  • The attic has gaps and penetrations that are hard to reach with batts or blown-in material.
  • You want to insulate a rim joist or an unfinished wall cavity before the finish goes on.
  • The existing insulation is worn out or has settled, and you want a continuous air barrier.
  • The house has a moisture problem in the crawl space or attic, and the contractor suggests a closed-cell foam.

What the pro does

  • Inspect the space and check for moisture, existing insulation, wiring, vents and any materials that the foam could cover.
  • Protect the rest of the house with sheeting, mask off the areas that should not be sprayed, and ventilate the work area.
  • Clean and dry the surfaces, and confirm the temperature and humidity are right for the foam type being used.
  • Spray the foam at the thickness the design calls for, in one or more passes, keeping the foam clear of recessed fixtures and vents.
  • Let the foam cure, then trim any overspray and check the coverage and the depth with a gauge.
  • Clear the work area, ventilate it as the foam cures, and tell the homeowner when the space is safe to re-enter.

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Foam type, such as open-cell or closed-cell, which have different materials and thicknesses.
  • Area to be sprayed and the thickness needed for the target.
  • Access to the space and the amount of masking and protection needed.
  • Whether the space has moisture or mold that must be fixed before the foam goes in.
  • Whether the job includes removal of old insulation, which adds time.
  • Whether ventilation or temporary relocation is needed while the foam cures.
  • Whether wiring or fixtures must be moved or protected.

What a written quote should spell out

  • The foam type and the thickness for each area.
  • The square footage covered, listed by space.
  • The masking, protection and ventilation steps included.
  • The moisture check, removal or repair work, listed separately.
  • The curing and re-entry time the homeowner should expect.
  • Warranty terms for the foam and the workmanship.

Questions to ask before you hire

  • Which foam type are you using, and why is it right for my space?
  • What thickness will you spray, and how will you check it?
  • Will you test the moisture in the space before you spray?
  • How will you protect the rest of the house, and how long will we be out of the space?
  • Are your applicators trained for this foam, and will the crew be on site the whole time?
  • How will you keep the foam away from recessed fixtures, the vents and the wiring?
  • What warranty covers the foam, and what does it not cover?

Red flags

  • The pro sprays foam over moisture or mold without fixing the source first.
  • The pro does not mask or protect the rest of the house, and cannot say how the work area is ventilated.
  • The pro cannot show the foam's data or the applicator training.
  • The pro covers recessed fixtures or wiring that the foam can affect.

What you can do yourself

Keep pets, children and anyone with breathing problems out of the house during the spray and cure, and clear the space of stored items. Tell the crew about any leaks or moisture you have seen. Do not spray, mix or handle the foam yourself, since application belongs to trained applicators, and do not re-enter until the crew says it is safe.

Licenses and permits

Spray foam insulation is often done by licensed or certified contractors, and applicators commonly need specific training and certification. Check with your state or local licensing agency for the requirements that apply to spray foam work in your area.

Spray foam insulation questions

Is spray foam safe in a home?

Once it has cured and the space has been ventilated, it is commonly used in homes. The foam chemicals are hazardous while they are being applied and cure, so the people in the house should stay out of the area until the crew says it is safe.

Why would I choose spray foam over batts?

Spray foam expands into gaps and seals them as it insulates, which batts cannot do. It is a more specialized install, so the choice depends on the space and the air leaks.

Can spray foam go over old wiring?

Not without an electrician checking it first. Foam over wiring can trap heat, and some foams must stay a set distance from recessed fixtures and certain electrical parts.

Do I need to ventilate after spray foam?

Yes, ventilate the space while the foam cures, as the crew directs. The crew tells you how long to keep the area closed and when it can be used again.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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