When homeowners start thinking about adding insulation to their homes, one question we hear a lot is: “Can you just inject the foam insulation into my walls from the attic?”
It sounds like a simple solution – just pour the foam down into the wall cavities and call it a day. Unfortunately, it’s not that easy. In fact, this method won’t properly insulate your walls at all.
Let’s break down why injecting foam insulation from the attic doesn’t work, and how professionals actually insulate existing walls the right way.
Here’s the thing: your walls aren’t big, open spaces.
Inside those wall cavities are all kinds of obstacles – fire stops, studs, electrical wires, plumbing, and windows – that prevent foam from flowing evenly down the wall.
Even if you could drill straight through the top plate (which you can’t, because it’s a solid 2x4 that caps the wall), the foam wouldn’t fill the entire cavity. It would hit an obstruction, spread unevenly, and leave large gaps with zero insulation.
That’s the opposite of what you want when trying to improve your home’s comfort and energy efficiency.
So while it might sound easier to pour insulation from above, you’d end up with spotty coverage and wasted material.
Absolutely – but it has to be done correctly.
You can insulate existing walls without tearing out drywall by injecting foam insulation from the outside. There is also the option to drill from the inside through the drywall, but never from the attic.
This process is minimally invasive and provides a complete, continuous layer of insulation that can dramatically improve comfort and energy efficiency.
If you really want to create an effective air seal and make your home more comfortable, here’s how professionals do it right.
The process of insulating existing walls with injection foam, like RetroFoam insulation, varies depending on your exterior – vinyl, wood, brick, or stucco.
Each exterior type requires a slightly different approach to ensure complete coverage.
Crews go around the entire house, drilling small holes into each stud cavity.
This allows them to access the space inside your walls – where the magic happens.
If your home has a vinyl or aluminum exterior, a row of siding is removed around the house, and holes are drilled into each stud cavity. If wood siding can’t be removed, holes are drilled through the boards to access the wall cavity.
The crew uses a special tool to check for obstructions by moving it up, down, and side-to-side in each cavity. If they find an obstruction, they’ll drill another hole above or below it. This ensures every section gets filled completely.
If the home has a brick or stucco exterior, the smaller holes are drilled at the top, middle, and bottom of each stud cavity.
Once each cavity is ready, the installer injects the foam.
As the material fills the space, it fills all of the nooks and crannies, creating an air seal inside the wall. That’s what helps eliminate drafts and cold spots throughout your home.
After the foam has been injected, the drilled holes are plugged, and if the siding was removed, it is replaced.
Injection foam insulation is one of the best ways to insulate finished walls in an existing home because it doesn’t require major demolition or interior disruption when done from the outside.
Here’s why injection foam is the best choice for existing walls:
If you’d like to see how the installation process looks for your specific siding type, visit our Learning Center to explore videos and articles on how RetroFoam is installed.
Adding Insulation to Exterior Walls: Installing RetroFoam with Different Siding Types
Insulating Exterior Walls from Inside with RetroFoam
Yes!
Injection foam can be installed from the exterior of your home without disturbing the interior drywall.
Absolutely.
By drilling small holes from the outside and injecting foam, experienced insulation contractors can insulate existing walls that likely have little to no insulation, depending on when they were built.