Can You Spray Foam Behind Drywall?

Your walls need more insulation. If there's any insulation in the walls, it isn't doing much. You'd like a non-invasive solution for your exterior walls. Is spray foam the solution you need so you won't have to remove your drywall or begin a remodel project?

South Central Services has insulated hundreds of existing homes around Greencastle, PA with spray foam. Many homeowners are seeking insulation upgrades to make their homes more comfortable and affordable to live in. While you can add spray foam to some areas of your home to boost energy efficiency, exterior walls are usually not one of these areas.

By the end of this article, you will understand:

• Why drywall causes accessibility issues for most insulations
• Why spray foam insulation cannot be installed behind drywall
• What insulation could be used in your exterior walls instead
• Where else spray foam can be installed in your home

Drywall Presents Accessibility Issues For Many Insulations.

When a new home is being constructed, there is a clear order of operations. The foundation has to be poured first. We build from the ground up. After there is a frame, insulation can be installed. The drywall is hung after insulation, and furnishings aren't brought inside until the home is nearly completed.

Insulating an existing home is a different process. The drywall is already hung, and there is no easy access to the wall cavities behind that drywall.

Batt insulation cannot be stuffed into these blocked cavities. While dense pack cellulose can be blown inside, it is a messy installation that has limitations. Dense pack requires drilling a hole between every stud so each cavity can be insulated. For these reasons, we avoid dense pack in this application.

Besides the apparent accessibility problems, drywall also obscures the substrate. There could be any number of issues inside a wall, including pest infestation or moisture. Even if batt insulation could be stuffed inside or dense pack could be blown inside, the installer has no way of knowing the conditions that insulation would face.

Spray Foam Insulation Cannot Be Installed Behind Drywall.

Since traditional insulations like fiberglass batts and blown-in products aren't suitable, many wonder if spray foam can solve this problem. After all, spray foam is a spray-applied product. Spray foam even expands after being sprayed.

At first glance, spray foam may seem like a perfect solution. However, the actual mechanics of this product make drywall an impossible obstacle, just like with traditional insulations. We only insulate the exterior walls of existing homes during major renovations when drywall is torn down.

There are two reasons why spray foam cannot be installed behind drywall.

1. Existing insulation must be removed
2. Spray foam requires spray technique

Let’s examine each of these in more detail.

1. Drywall Prevents The Removal Of Existing Insulation.

Spray foam insulation can only be installed after removing any existing insulation. We sometimes get this question when homeowners want to upgrade attic insulation. No matter how much money was invested in batt or blown-in solutions, all of that insulation must be removed before installing spray foam.

Spray foam works by adhering to the substrate it is sprayed against. Any existing insulation compromises the seal and adhesion of the foam.

Since drywall is firmly in place, removing existing insulation is next to impossible.

For the sake of argument, let's assume that your exterior walls don't have any insulation in them. Why can't spray foam be the solution for your intact walls?

2. Spray Foam Insulation Adheres In Place When Sprayed.

Even if the wall cavities are completely empty, drywall still causes accessibility problems.

When spray foam is installed, it adheres in place. While spray foam insulation may look as simple as pointing and spraying, properly installing it requires training and technique.

As you can see in the video above, these open wall cavities have spray foam installed in the edges before spraying the center of the cavity. This technique, called window framing, ensures that spray foam adheres in the crevices of the wall cavity. Without window framing, the application could have gaps or air pockets.

No matter how you approach spray foam with drywall, it doesn't work. If you tried to spray from above, you could not properly adhere to anything. You would just be aimlessly filling the cavity with pockets of foam.

Accessing the walls incrementally from inside or outside the home cannot work, either. Entry points small enough to fit the spray nozzle without causing significant damage cannot provide enough accessibility.

There is a range of motion that spray foam installation requires, and drywall cannot be worked around.

What Else Can Be Done To Better Insulate Your Home?

At this point, you may be pretty frustrated. What are you supposed to do if expanding foam cannot insulate your exterior walls?

There are two pieces of good news.

Injection Foam Can Be Used In Existing Walls With Drywall.

While spray foam insulation cannot be used in exterior walls, another kind of expanding foam insulation has had some success for exterior walls.

Injection foam is different than spray foam insulation, although many online resources conflate the two. Injection foam is made up of ingredients different from spray foam insulation. Injection foam is also a slow-rising foam.

Open cell spray foam expands almost instantaneously, while injection foam takes time for its chemical reaction to complete.

The entire purpose behind injection foam is to solve the adhesion and accessibility challenges that spray foam faces with intact drywall. Unfortunately, injection foam cannot solve the problem of existing insulation.

Like spray foam, injection foam should only be installed in an empty wall cavity. Any insulation in the exterior wall cavities can become trapped by the foam or prevent the foam from reaching the entire cavity. Additionally, the existing insulation may have moisture or mold problems.

South Central Services only recommends injection foam for homes without insulation in the exterior walls. Even then, we recommend looking into other insulation upgrades with fewer risks.

We have seen too many homeowner testimonials of injection foam gone wrong when the presence of existing insulation was ignored. This is the main reason why we do not install injection foam ourselves. We can be confident when installing spray foam insulation in accessible areas of a home's thermal envelope. In these accessible retrofit areas, we can control the application, chemical reaction, and result.

If Drywall Is An Obstacle, Consider Other Insulation Upgrades.

What's the other good news? Other areas of your home are accessible for spray foam upgrades. While you might not be able to put spray foam insulation in your walls, you can insulate other critical areas of your thermal envelope.

When we approach a poorly insulated home, our attention goes to the attic, basement, and crawl space. Not every home has all three of these areas, but these places are where we like to start.

Just like your exterior walls, your attic and your below-grade spaces are part of the home's thermal envelope. They form the barrier between your comfortable interior and the outside temperatures. Unlike your exterior walls, these areas are accessible.

No drywall is blocking the way for spray foam insulation in an attic, basement, or crawl space. We can seamlessly apply spray foam insulation and deliver an airtight seal. We can also offer a vapor barrier in below-grade areas like the basement and crawl space. All of these features help to protect your home from air infiltration problems.

These upgrades translate to lower energy costs, a more comfortable home, and better indoor air quality. When your conditioned air cannot randomly escape the house, you pay less to maintain your desired temperature.

The Bottom Line About Why Spray Foam Can’t Be Used Behind Drywall

Spray foam insulation is a premium product that delivers a high R-value and an airtight seal. However, spray foam is also a complex product that a trained contractor should install. For spray foam to adhere and offer superior performance, it must be installed correctly.

Drywall gets in the way of that correct installation. Not only does drywall hide any problems and existing insulation within the wall cavities, but it also blocks the range of motion necessary for spray foam.

For some homes, injection foam can be an alternative for exterior wall insulation. This product resolves the accessibility problems of spray foam but should only be used in empty wall cavities.

If your wall cavities have some existing insulation or you are more interested in spray foam insulation, you can upgrade the insulation in your attic, basement, or crawl space instead.

Now that you know why spray foam can’t be installed behind drywall, your next step is to:

• Discover if your attic has enough insulation
• Learn where to insulate in your basement
• Compare vented and encapsulated crawl spaces