It seems like it should work, and that insulating your existing walls through the attic would be the quickest and easiest way.
I thought the same thing before I started working in the foam insulation industry. Now I know this not only isn’t the best practice but could leave homeowners not fully covered.
RetroFoam of Michigan has more than 15 years of experience insulating homes across the lower peninsula. I myself have more than a dozen years of experience working with homeowners to solve the problems they are experiencing.
With my experience, I understand how the injection foam insulation works and what is the best way to install it. Let’s take a deeper look at this installation myth, and why it won’t work in your home.
Installing Foam Insulation in Existing Walls
Out of 10 homes, I give an estimate to, at least four of those homes ask if insulating the exterior walls with injection foam can be done through the attic or soffit.
It might seem like the easier option to just inject from the top down, but in reality, this isn’t an effective method at all.
There are two problems with trying to add exterior wall insulation this way.
First of all, at the top of the wall, there is a thing called a top plate. This top plate doesn’t give an installer the room they need to drill into the wall cavity and run the hose in to inject the foam. So, this first issue comes down to there just not being enough space to work in.
The second problem is there’s no way to account for any stops and windows that could get in the way of the installation. This could leave a homeowner with gaps in their insulation coverage.
The best and most common way to insulate existing walls with injection foam insulation is from the outside.
Injection Foam Insulation Installation Process
Installing injection foam in your existing exterior walls is quick, simple, and usually can be done in just one day.
In most cases, we insulate those exterior walls from the outside, but we have injected the foam from the inside when needed. The installation process can vary slightly depending on the type of siding you have on your home.
For homes with aluminum or vinyl siding, installation crews will remove a piece and drill a hole into each stud cavity. A member of the crew will then run a Slim Jim up and down the cavity to ensure there are no fire stops or studs that will inhibit the hose and to feel for the next stud. This method gives the installer a good idea of the cavity size from top to bottom and side to side.
RELATED: How Do Crews Know if the Wall Cavity is Full When Injecting Foam Insulation?
The injection hose is then run-up to the top of the stud cavity and then all the way down to the bottom. If there are any obstructions, another hole will be drilled in the cavity to ensure it is completely filled.
Once the installation is complete, the drilled holes are plugged, and the siding is replaced.
The process for wood and brick siding is slightly different.
Wood siding can possibly be removed depending on the condition it is in. If we can’t remove it, then the crew would drill through it to inject the foam. Those holes would be plugged with a tapered wood plug.
Homes with brick siding can be done without removing any of the bricks.
A 5/8-inch hole is drilled through the mortar joints to inject the foam. Once installation is finished, those holes are re-mortared with a standard gray mortar.
Learning More About Foam Insulation
Now that I have dispelled the myth about injection foam insulation, you might be curious to learn even more truths about the material.
If you are ready to continue your foam insulation educational journey, check out the Learning Center on our website.
RELATED: Clearing Up Misconceptions about Spray Foam Insulation
