The open cell spray foam you see sprayed into new walls can’t go into a wall that already has drywall on it. It comes out of a spray gun, expands about 100 times in seconds, and has to be laid on in passes that the installer can see. Inside a closed wall, nobody can see it, aim it or trim it, so it leaves voids or pushes on the drywall. For finished walls, the products that work are injection foams made for closed cavities, dense-pack cellulose and blown fiberglass.
Homeowners ask us for “spray foam in the walls” all the time, usually after hearing how well it seals. We get why. Our Grizzly Insulation Co crews spray open cell foam in Denver homes every week, so here’s the honest reason we won’t spray it into your finished walls, and what we do instead.
How Does Open Cell Spray Foam Get Installed?
It goes onto open framing before drywall. Two liquids mix at the gun, hit the sheathing and puff up within seconds. The installer works in passes, watching the depth, then trims any extra flush with the studs. Our guide to SPF insulation shows how it works.
That process needs eyes on the foam. The crew has to see each cavity fill to the right depth and catch any gaps around wires or boxes.
Why Can't Open Cell Spray Foam Go Into a Closed Wall?
Because you can’t see or steer it. Through a small hole, the foam fills whatever is closest to the nozzle first. It can skip spots behind wires and fire blocks and leave empty pockets. Push in too much and the fast rise can bow or crack the drywall.
There’s also no way to trim it. Extra foam has nowhere to go, and you can’t check the finished depth without opening the wall anyway.
Is There Any Foam That Works in Existing Walls?
Yes, but it’s a different product. The Department of Energy’s guide to types of insulation notes that some foams are made to be injected into wall cavities. These injection foams rise slowly and gently, so they flow around obstacles without pushing the drywall out.
Only if the siding and sheathing come off. Then the wall is open again, and open cell or closed cell foam can be sprayed normally. That makes sense during a full re-side, but rarely on its own.
You’ll sometimes hear that any foam “pumped into the walls” is the same as spray foam. Nobody has shown that. Regular spray foam and injection foam are different chemistry with different rise speeds. Asking an installer which one they’re using is fair, and our blog on injection foam vs spray foam lays out the differences.
Can You Remove Just a Strip of Drywall to Spray Foam?
Sometimes, but it rarely saves much. Some crews cut a strip of drywall near the top or bottom of each wall to reach the cavity. The trouble is that a spray gun still can’t reach the whole bay from a narrow slot, so voids are likely.
It works better for small areas, like a single wall in a remodel or a band joist you can reach from a closet. For whole walls, dense-pack or injection foam through small holes is cleaner. Our insulation removal team can pull old batts out first if a wall does get opened.
Is It Worth Opening the Drywall for Spray Foam?
Usually not just for insulation. Removing and replacing drywall, plus taping and painting, often costs more than the foam. During a big remodel, though, when the walls are open anyway, it’s a great time to spray.
If your house were ours, we’d use dense-pack or injection foam in closed walls and save spray foam for open walls, rim joists and attics. That’s how we approach most Denver homes. Our spray foam insulation team can tell you where it fits best.
How Long Does It Take to Insulate Closed Walls?
Most homes take one to three days. The crew finds each stud bay, drills a small hole near the top, fills the cavity and plugs the hole. Holes can go in from outside under the siding or from inside through the drywall.
Injection foam needs a little curing time, while dense-pack cellulose is ready right away. Either way, you’ll need some light patching and paint afterward. On a typical Denver bungalow with plaster walls, we usually work from the outside to keep the mess out of your rooms. There’s more on the method in our foam injection guide.
Do Closed Denver Walls Even Need Insulation?
Many older ones do. Plenty of Denver homes built before the 1970s have empty or half-full walls. Cold outside walls, drafts at outlets and rooms that never warm up are the usual clues. Our list of signs your home needs better insulation covers more.
Choose the Right Insulation for Existing Walls in Your Denver Home
Open cell spray foam needs open walls. For finished walls, injection foam, dense-pack cellulose and blown fiberglass do the job without tearing anything out. Pick the method that matches the wall you have.
Want warmer walls without demolition in your Denver home? Grizzly Insulation Co can help. We’re BPI Certified and an Xcel Energy rebate partner.
Why Open Cell Spray Foam Insulation Can’t Go Into Existing Closed Walls
The open cell spray foam you see sprayed into new walls can’t go into a wall that already has drywall on it. It comes out of a spray gun, expands about 100 times in seconds, and has to be laid on in passes that the installer can see. Inside a closed wall, nobody can see it, aim it or trim it, so it leaves voids or pushes on the drywall. For finished walls, the products that work are injection foams made for closed cavities, dense-pack cellulose and blown fiberglass.
Homeowners ask us for “spray foam in the walls” all the time, usually after hearing how well it seals. We get why. Our Grizzly Insulation Co crews spray open cell foam in Denver homes every week, so here’s the honest reason we won’t spray it into your finished walls, and what we do instead.
How Does Open Cell Spray Foam Get Installed?
It goes onto open framing before drywall. Two liquids mix at the gun, hit the sheathing and puff up within seconds. The installer works in passes, watching the depth, then trims any extra flush with the studs. Our guide to SPF insulation shows how it works.
That process needs eyes on the foam. The crew has to see each cavity fill to the right depth and catch any gaps around wires or boxes.
Why Can't Open Cell Spray Foam Go Into a Closed Wall?
Because you can’t see or steer it. Through a small hole, the foam fills whatever is closest to the nozzle first. It can skip spots behind wires and fire blocks and leave empty pockets. Push in too much and the fast rise can bow or crack the drywall.
There’s also no way to trim it. Extra foam has nowhere to go, and you can’t check the finished depth without opening the wall anyway.
Is There Any Foam That Works in Existing Walls?
Yes, but it’s a different product. The Department of Energy’s guide to types of insulation notes that some foams are made to be injected into wall cavities. These injection foams rise slowly and gently, so they flow around obstacles without pushing the drywall out.
Our blog on injection foam installation walks through how it’s done.
What Are the Other Options for Insulating Closed Walls?
There are two common ones besides injection foam:
Our blown-in insulation teams handle both. We cover the whole process in our guide for insulating existing interior walls.
Can You Spray Foam a Wall From the Outside?
Only if the siding and sheathing come off. Then the wall is open again, and open cell or closed cell foam can be sprayed normally. That makes sense during a full re-side, but rarely on its own.
You’ll sometimes hear that any foam “pumped into the walls” is the same as spray foam. Nobody has shown that. Regular spray foam and injection foam are different chemistry with different rise speeds. Asking an installer which one they’re using is fair, and our blog on injection foam vs spray foam lays out the differences.
Can You Remove Just a Strip of Drywall to Spray Foam?
Sometimes, but it rarely saves much. Some crews cut a strip of drywall near the top or bottom of each wall to reach the cavity. The trouble is that a spray gun still can’t reach the whole bay from a narrow slot, so voids are likely.
It works better for small areas, like a single wall in a remodel or a band joist you can reach from a closet. For whole walls, dense-pack or injection foam through small holes is cleaner. Our insulation removal team can pull old batts out first if a wall does get opened.
Is It Worth Opening the Drywall for Spray Foam?
Usually not just for insulation. Removing and replacing drywall, plus taping and painting, often costs more than the foam. During a big remodel, though, when the walls are open anyway, it’s a great time to spray.
If your house were ours, we’d use dense-pack or injection foam in closed walls and save spray foam for open walls, rim joists and attics. That’s how we approach most Denver homes. Our spray foam insulation team can tell you where it fits best.
How Long Does It Take to Insulate Closed Walls?
Most homes take one to three days. The crew finds each stud bay, drills a small hole near the top, fills the cavity and plugs the hole. Holes can go in from outside under the siding or from inside through the drywall.
Injection foam needs a little curing time, while dense-pack cellulose is ready right away. Either way, you’ll need some light patching and paint afterward. On a typical Denver bungalow with plaster walls, we usually work from the outside to keep the mess out of your rooms. There’s more on the method in our foam injection guide.
Do Closed Denver Walls Even Need Insulation?
Many older ones do. Plenty of Denver homes built before the 1970s have empty or half-full walls. Cold outside walls, drafts at outlets and rooms that never warm up are the usual clues. Our list of signs your home needs better insulation covers more.
Choose the Right Insulation for Existing Walls in Your Denver Home
Open cell spray foam needs open walls. For finished walls, injection foam, dense-pack cellulose and blown fiberglass do the job without tearing anything out. Pick the method that matches the wall you have.
Want warmer walls without demolition in your Denver home? Grizzly Insulation Co can help. We’re BPI Certified and an Xcel Energy rebate partner.
Frequently Asked Questions
Regular spray foam can’t. Injection-grade foams are made for closed walls.
Dense-pack cellulose, blown fiberglass or injection foam.
It shouldn’t when installed right. It rises slowly and gently.
No. It’s sprayed too, so the same problems apply.