How to Insulate a Garage That Already Has Drywall Up?

You can insulate a finished garage by drilling 4” holes in the drywall to fill each stud bay with blown-in insulation. Cellulose and stonewool can be blown through these holes to insulate garage walls and ceilings that already have drywall on them.

An alternative is to strip the drywall completely to install insulation batts. Drywall can then be installed back and screwed into the wall studs or replaced with new drywall or other materials such as OSVB.

Insulating a finished garage seems like a complicated task. The biggest problem when you want to insulate a garage that already has drywall up is losing money by tearing existing drywall or by doing a poor insulation hob. In some cases, you can lose money by hiring expensive contractors, but the job is DIY if you know what to do and where to get the tools you need from.

2 Ways to insulate a finished garage that already has drywall up?

You can insulate a finished garage with blow-in insulation. This can be done by cutting holes in the drywall. A 4” hole should be enough.

If the theory is easy practice is where you will encounter all types of problems in.

1. Blow-in cellulose insulation technique

Blow-in cellulose is the least intrusive method of insulating garage walls and garage ceilings that are already finished. Garage walls with drywall installed are normally based on a wooden frame with studs installed at 16”. Insulation can be blown between these studs when you drill holes in the drywall for the insulation blower to get inside.

You can borrow a cellulose blower from Home Depot or Lowe’s

Renting out equipment is the easiest way to insulate a garage that already has drywall up when you’re on a budget. The big stores such as Home Depot and Lowe’s should have this equipment available for a quick job.

Blow cellulose insulation between studs

A garage that already has drywall installed can be insulated with blow-in cellulose without completely removing drywall. Blown-in cellulose is the easiest choice for most homes.

For garages that are next to the house, you need to think about fire safety as well. Noncombustible insulation is ideal when you have at least one common garage-house wall. Stonewool (R14) is one of the best non-flammable types of insulation for garage walls and garage ceilings.

Heat rises quickly and you need to start garage insulation with ceilings first. This is where you want to completely cover all areas with blow-in insulation.

If you’re afraid your garage might suffer from high humidity there are all types of non-organic insulation materials you can consider. Even if you have humidity levels above average in your garage stoneweool isolation is not going to retain that humidity. Synthetic insulation prevents moisture even behind drywall on your garage’s walls and ceiling. Check out the best place to buy insulation in our latest garage shopping guide.

2. Insulating garage walls already drywalled by stripping the sheetrock

A simpler but more expensive method is to strip the drywall and go for higher-grade insulation such as insulation batts. You can remove drywall individually and then use a type of synthetic insulation to add thermal protection to your garage which might equate to a warmer climate by a few degrees.

Using OSB instead of drywall

When the insulation is installed between the studs you have the option of either putting drywall back up or adding OSB panels instead. Make sure your garage is not next to your home as OSB is not a fire-safe material. Metal cladding can also be an option when it comes to finishing up garage walls. We took a closer look at cheap garage wall covering in a recent article.

Final words

A garage is best insulated with blow-in insulation cellulose when drywall is already installed. If drywall can be removed fiberglass or stonewooll batts are preferable between the studs before placing the sheetrock back.


Is insulating a garage worth it?

Yes, insulating a garage is worth it. Insulated walls and ceilings add thermal protection of at least a few degrees as well as better sound insulation.

Do you need a vapor barrier when insulating a garage?

Garage walls and ceilings are normally installed with a vapor barrier. This is a must in high-humidity garages. But ensuring proper ventilation is still required to prevent mold formation.

Can you drywall an unheated garage?

Yes, you can drywall an unheated garage but only as long as it doesn’t have high humidity. Cold temperatures aren’t going to damage drywall as much as high air humidity.

Do you need mold-resistant drywall in your garage?

Mold-resistant drywall is ideal to prevent mold formation. Make sure to install a good ventilation system in your garage first if measurements indicate high air humidity.