Spray foam is a modern form of insulation that is fast to install, offers great R value, and stops drafts that pull air from your home. Spray foam insulation can be installed nearly anywhere in a home, but there are areas you should avoid.

Generally, you can install spray foam in walls, attics, and crawl spaces as long as you follow a few safety rules. For example, never apply spray foam insulation around a heat source like a furnace door or gas pilot light. Spray foam is flammable and can emit harmful gasses like carbon monoxide if it ignites.

Spray foam fills in the tiny gaps and spaces that leak conditioned air from your home, helping maintain a constant temperature inside. Because the foam expands up to 3x its original size, you must exercise caution and not overfill a void. 

Here we will discuss where you can apply spray foam insulation and areas you should avoid. 

Spray Foam In Attic: YES 

Spray foam insulation is great for attics with a floor as well as vaulted and cathedral style attics. Attic insulation can be installed between and over ceiling joists and trusses, between the rafters, or both.

Spray foam insulation has the insulation effectiveness of fiberglass batts, seals gaps better than caulk, and installs very quickly like loose fill. Spray foam insulation is great for attics because it does not hold moisture, compact, or require fasteners.

Spray foam is available in several configurations, but can be generally separated into open cell and closed cell formulations. Open cell spray foam insulation is the kind you find in a small can with an applicator spray tube. Open cell is great for filling small gaps around doors and windows.

Closed cell spray foam insulation is the best option for insulating an attic because it has more R value per inch than open cell foam. Closed cell foam is more dense than open cell foam although it does not expand as much, making it ideal for large areas.


  • Creates a vapor barrier as it cures
  • Does not settle or compact
  • Resistant to moisture, reducing mold and mildew
  • Closed cell foam has nearly double the R value of fiberglass


  • Safety gear and training is required to install
  • Relatively expensive

Spray foam insulation is applied using pressurized chemicals that mix together as they exit a spray nozzle, forming a sticky foam. As the foam expands it traps tiny air pockets inside the foam, which act as a thermal barrier.

Spray foam insulation can replace cellulose, loose fill fiberglass, fiberglass batts, or mineral wool in an attic. Spray foam will not harbor nearly as much moisture as these other options, making it a superior choice as a low maintenance material.

Summary: Spray foam insulation is a great choice for any type of attic space. 

Spray Foam In Interior Walls: YES 

Spray foam insulation is an excellent choice for insulating interior walls because it provides excellent sound deadening. Interior walls are primarily insulated for sound absorption, like between a living room and a home theater, or to keep one room warmer than another. 

Closed cell spray foam is the best option for walls because it can provide an R value of about 20 in a 2” x 4” stud wall. For comparison, fiberglass batts provide less than half as much R value by volume, so the batts must be thicker than spray foam to achieve the same R value.

Other insulation options include mineral wool and loose fill, but these do not offer the speed, effectiveness, or durability of spray foam insulation.

Summary: Spray foam insulation is an excellent choice for insulating walls.

Spray Foam In Exterior Walls: YES 

Spray foam is excellent for exterior walls due to its ability to insulate and seal at the same time. Depending on the building codes where you live, exterior walls may need to contain as much as R-19 insulation. Spray foam can surpass this R value in a 2” x 4” wall, but most fiberglass batts would require a 2” x 6” wall to achieve the same R value.

In most installations, closed cell spray foam insulation is sprayed between the wall studs and allowed to expand. After fully curing (about 24 hours), professionals use a heated wire or sharp blade to trim away any excess insulation that may have expanded beyond the studs to maintain a flat surface for drywall.

Other options include mineral wool and fiberglass batts, as well as loose fill in certain situations. However, none can compare with the effectiveness, installation speed, and durability of spray foam, making it ideal for exterior walls.

Summary: Spray foam insulation is excellent for insulating exterior walls.

Spray Foam In Basement: YES

Spray foam insulation can work great in a finished basement wall as long as a stud wall is present as well. If the basement is unused the spray foam can be applied directly to the concrete or block wall, just as in a crawl space.

Spray foam is also the first choice for insulating between floor joist or trusses because the product does not require a vapor barrier, additional sealing, or mechanical fasteners. Traditionally this space would be insulated with fiberglass batts, which require additional sealing and staples to achieve the same result.

However, if the basement will be finished as living space, the spray foam will need to be covered with drywall or other durable wall covering. This means either building a stud wall parallel to the masonry or installing furring strips on the masonry to attach the wall covering to.

Spray foam insulation can be applied directly to basement walls if the space will just serve as storage or will remain empty. 

Summary: Spray foam insulation is excellent for use in a basement.

Spray Foam In Ceiling: YES 

Closed cell spray foam insulation is fantastic for ceilings because it works just as well for vaulted ceilings as it does for flat ceilings. Modern construction is most done using trusses, which is very friendly to vaulted and cathedral ceilings. This is why you often see vaulted ceilings in even moderately priced homes.

Traditionally, loose fiberglass or cellulose was the first choice for ceiling insulation because it was DIY friendly, cost effective, and had a long lifespan. However, these are most effective on flat ceilings because they rely on gravity to remain in place. Loose fill insulation used in a vaulted ceiling will gather at the lowest point, making it less effective and inconsistent.

Before spray foam, fiberglass and mineral wool batts were popular for vaulted ceilings because they relied on either compression or mechanical fasteners instead of gravity. However, spray foam eliminates the need for tight fits and staples, relying on its sticky texture for adhesion.

Summary: Spray foam is a great insulation material for any type of ceiling.

Spray Foam In Roofing: Maybe

Open cell spray foam is a common sight around roofs, eaves, dormers, and chimneys. However it should be noted that spray should not be used outdoors unless it will be protected. Spray cannot be left out in the elements, so it must be covered with flashing, siding, caulk, or other exterior grade sealant.

However, spray foam is much better at sealing air gaps than caulk because it does not move once it cures. Caulk will often either harden and become brittle, or be pulled so hard by warm, expanding wood and detach.

Open cell spray foam is commonly applied from the roof to dormer windows and chimneys, but will always be covered with an exterior grade material. 

Summary: Spray foam insulation can be used around the roof, but it must be protected.

Spray Foam in Garage: YES 

Spray foam insulation is awesome for garages, whether they are attached or detached. ADUs (accessory dwelling units) are often found above garages, as are storage lofts. Insulation is critical to both the garage and any space above it, and none work better than spray foam.

If your garage is built from masonry, metal, or wood framing you can apply spray foam effectively. However, you will need to vary your technique depending on the design of the garage. 

If your garage has stud walls, you can apply the spray foam just as you would inside the home, using a spray foam kit. If no studs are present and the space is used often, consider adding a wooden stud wall, as it will make using any insulation easier, and provide a place for the wall covering.

It is not recommended to apply spray foam directly to a metal building using older spray foam technology as these products may be acidic and accelerate corrosion. Condensation can form, leading to wet floors and mold growth

Garages are traditionally insulated with fiberglass batts or loose fill. Spray foam is faster, more effective, and more adaptable than either batts or blown in insulation. However, spray foam does generally cost more to purchase and install than batts or loose fill.

Summary: Spray foam insulation is awesome for any garage.

Spray Foam Crawl Space: YES 

Spray foam insulation is without a doubt the best option for insulating a crawl space. Crawl space walls are notoriously difficult to insulate with batts, mineral wool, or any insulation that requires fasteners.

Spray foam is perfect for crawl space walls because it requires no additional construction, sticks to uneven surfaces, and will not absorb moisture like fiberglass batts. Closed cell spray foam is the most common option because as mentioned earlier, it works best in large areas.

Closed cell spray foam should not be applied to damp crawl space walls, so pros use fans to dry the surface before applying the foam directly to the masonry. The foam is also ideal for the floor above. Usually sprayed between the floor trusses, spray foam will also add significant rigidity to the floor system.

Summary: Spray foam insulation is perfect for crawl spaces.

Spray Foam Between Floors: MAYBE

Generally, insulating between floors is treated like insulating interior walls. Since both sides of the floor are heated and cooled, insulation is typically only installed to either dampen sound transmission between floors or to control different temperatures from floor to floor.

Insulating between floors is common in apartments of course, because they are not necessarily the same temperature and may not share a love of drums. 

In a residential home, spray foam is ideal for insulating between floors, but the foam must remain clear from recessed light fixtures and fan motors that may reside between the floors. Keep spray foam at least 2” from recessed light fixtures, bathroom vent fans, and other generators of heat.

Summary: Spray foam is great for insulating between floors as long as precautions are taken.

Where Should Spray Foam Insulation Not Be Used?

Spray foam insulation, whether open cell foam or closed cell, has a few limitations to where it can be used. Here is a partial list of locations where fiberglass batts and styrofoam insulation are a better option than spray foam and a few places where spray foam is prohibited:

  • Near any source of open flame
  • Within 2” of a recessed can light (unless the fixture is rated for contact)
  • Around bathroom vent fans 
  • Within 2” of a dryer exhaust vent
  • Near ovens, furnaces, ranges, or grills
  • Outdoors, unless it will be protected
  • PEX tubing manifolds and recirculation pumps

Justin's been in construction for over 20 years in both new build and renovation. With experience in both commercial and residential construction, he specializes in healthier and more energy-efficient homes.

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