For an attached garage, the best insulation goes on the wall you share with the house. Use fiberglass or mineral wool batts, seal every gap so car fumes stay out, and cover the garage side with drywall as the fire code requires. The outside garage walls only matter if you heat the space. For a detached garage, skip insulation unless you plan to heat it or use it as a workshop. If you do, closed cell spray foam or batts with a vapor-smart facing are the usual picks.
Garages are confusing because they’re half outdoors and half part of the house. Our Grizzly Insulation Co crews insulate both kinds in Denver every month, so here’s how we decide what each one needs.
Do You Need to Insulate Garage Walls at All?
It depends on how the garage connects to the house. The wall between an attached garage and your living space acts like an outside wall. Heat leaks through it, and so can exhaust fumes.
A detached garage is different. If you never heat it, insulating it does little for your energy bills. Our main guide to insulating a garage covers doors and ceilings too.
What Is the Best Insulation for an Attached Garage Wall?
Batts in the shared wall, plus careful air sealing. Here’s what we recommend:
Shared wall: R-13 or R-15 batts in a 2×4 wall, R-19 to R-23 in a 2×6. See R-15 insulation.
Mineral wool if you want extra fire resistance and sound control.
Air seal around outlets, pipes and the house door.
Outside garage walls: only if you heat the garage.
What Does the Code Require for Attached Garage Walls?
Fire separation, not R-value. The International Residential Code’s garage rules, summarized in this residential garage separation tip sheet, call for at least half-inch drywall on the garage side of the shared wall. Rooms above the garage need 5/8-inch Type X drywall on the ceiling below. The door into the house must be solid or fire-rated and self-closing.
That means any insulation in that wall should be covered by drywall on the garage side. Foam can’t be left exposed there.
Why Does Air Sealing Matter So Much in an Attached Garage?
Because garages hold car exhaust, gas cans and lawn chemicals. Gaps in the shared wall let those fumes drift into your home. Insulation alone doesn’t stop air.
You may hear that a well-insulated wall “blocks fumes.” Nobody has shown that batts stop air movement. They slow heat, not air. If your garage were ours, we’d caulk and foam every gap in that wall before any insulation goes in. Our air sealing service handles it.
What Is the Best Insulation for a Detached Garage?
Only insulate it if you heat it. For a heated workshop:
Closed cell spray foam for metal or pole buildings. It seals, insulates and stops condensation on steel. See what closed cell spray foam is.
Batts in a wood-framed detached garage, covered with drywall or plywood.
An insulated garage door, since the door is often the biggest wall in the building.
If there’s a bedroom or bonus room above the garage, yes. That floor is one of the coldest spots in many Denver homes, because cold garage air sits right under it. The ceiling needs insulation that touches the subfloor above, plus air sealing around ducts and pipes.
For a garage with only attic space above, insulate the attic floor like any other attic. Our blog on ceiling insulation R-value shows the targets, and R-13 insulation covers the common wall batt.
Does an Insulated Garage Door Matter as Much as the Walls?
The big door is often the largest single wall surface, and a thin steel door leaks heat fast. Insulated doors or door panel kits help, and so does a new bottom seal.
In an attached garage you don’t heat, the door matters less for your energy bill. The shared wall and the ceiling under any rooms above come first. Our blog on a cold draft in the house explains how garage air can sneak into living space.
Should Garage Wall Insulation Be Faced or Unfaced?
It depends on which side is heated. The paper facing on batts usually goes toward the warm side. In a heated garage, that’s the garage side. On the shared wall of an unheated attached garage, it’s the house side. Our blog on faced vs unfaced insulation explains the rule.
Can Mice Get Into Garage Wall Insulation?
They try. Garages are a favorite entry point for mice in Denver, especially in fall. Sealing gaps at the bottom of walls and around the garage door keeps them out. See pest-resistant insulation for materials they don’t like.
Is Insulating Garage Walls Worth It in Denver?
For the shared wall of an attached garage, almost always. It warms the rooms next to the garage and keeps fumes out. A detached garage is only worth insulating if you’ll heat it through Denver winters.
Choose the Best Insulation for Garage Walls Based on How You Use the Space
For an attached garage, insulate and seal the shared wall first. For a detached garage, insulate only if you heat it. Match the material to the building, and cover it the way code requires.
Want your garage done right in Denver? Grizzly Insulation Co can help. We’re BPI Certified and an Xcel Energy rebate partner.
The Best Insulation for Garage Walls in Attached vs Detached Garages
For an attached garage, the best insulation goes on the wall you share with the house. Use fiberglass or mineral wool batts, seal every gap so car fumes stay out, and cover the garage side with drywall as the fire code requires. The outside garage walls only matter if you heat the space. For a detached garage, skip insulation unless you plan to heat it or use it as a workshop. If you do, closed cell spray foam or batts with a vapor-smart facing are the usual picks.
Garages are confusing because they’re half outdoors and half part of the house. Our Grizzly Insulation Co crews insulate both kinds in Denver every month, so here’s how we decide what each one needs.
Do You Need to Insulate Garage Walls at All?
It depends on how the garage connects to the house. The wall between an attached garage and your living space acts like an outside wall. Heat leaks through it, and so can exhaust fumes.
A detached garage is different. If you never heat it, insulating it does little for your energy bills. Our main guide to insulating a garage covers doors and ceilings too.
What Is the Best Insulation for an Attached Garage Wall?
Batts in the shared wall, plus careful air sealing. Here’s what we recommend:
Our batt insulation tean does this work regularly.
What Does the Code Require for Attached Garage Walls?
Fire separation, not R-value. The International Residential Code’s garage rules, summarized in this residential garage separation tip sheet, call for at least half-inch drywall on the garage side of the shared wall. Rooms above the garage need 5/8-inch Type X drywall on the ceiling below. The door into the house must be solid or fire-rated and self-closing.
That means any insulation in that wall should be covered by drywall on the garage side. Foam can’t be left exposed there.
Why Does Air Sealing Matter So Much in an Attached Garage?
Because garages hold car exhaust, gas cans and lawn chemicals. Gaps in the shared wall let those fumes drift into your home. Insulation alone doesn’t stop air.
You may hear that a well-insulated wall “blocks fumes.” Nobody has shown that batts stop air movement. They slow heat, not air. If your garage were ours, we’d caulk and foam every gap in that wall before any insulation goes in. Our air sealing service handles it.
What Is the Best Insulation for a Detached Garage?
Only insulate it if you heat it. For a heated workshop:
Our spray foam insulation team handles metal buildings and shops.
Should You Insulate the Garage Ceiling Too?
If there’s a bedroom or bonus room above the garage, yes. That floor is one of the coldest spots in many Denver homes, because cold garage air sits right under it. The ceiling needs insulation that touches the subfloor above, plus air sealing around ducts and pipes.
For a garage with only attic space above, insulate the attic floor like any other attic. Our blog on ceiling insulation R-value shows the targets, and R-13 insulation covers the common wall batt.
Does an Insulated Garage Door Matter as Much as the Walls?
The big door is often the largest single wall surface, and a thin steel door leaks heat fast. Insulated doors or door panel kits help, and so does a new bottom seal.
In an attached garage you don’t heat, the door matters less for your energy bill. The shared wall and the ceiling under any rooms above come first. Our blog on a cold draft in the house explains how garage air can sneak into living space.
Should Garage Wall Insulation Be Faced or Unfaced?
It depends on which side is heated. The paper facing on batts usually goes toward the warm side. In a heated garage, that’s the garage side. On the shared wall of an unheated attached garage, it’s the house side. Our blog on faced vs unfaced insulation explains the rule.
Can Mice Get Into Garage Wall Insulation?
They try. Garages are a favorite entry point for mice in Denver, especially in fall. Sealing gaps at the bottom of walls and around the garage door keeps them out. See pest-resistant insulation for materials they don’t like.
Is Insulating Garage Walls Worth It in Denver?
For the shared wall of an attached garage, almost always. It warms the rooms next to the garage and keeps fumes out. A detached garage is only worth insulating if you’ll heat it through Denver winters.
Choose the Best Insulation for Garage Walls Based on How You Use the Space
For an attached garage, insulate and seal the shared wall first. For a detached garage, insulate only if you heat it. Match the material to the building, and cover it the way code requires.
Want your garage done right in Denver? Grizzly Insulation Co can help. We’re BPI Certified and an Xcel Energy rebate partner.
Frequently Asked Questions
R-13 to R-15 in 2×4 walls and R-19 to R-23 in 2×6 walls.
On the shared wall of an attached garage, yes. Code requires drywall on the garage side.
Yes, especially in metal or heated detached garages.
Only if you plan to heat it or use it as a workshop.
Yes, along with insulating the garage ceiling under those rooms.