How To Insulate A Garage Ceiling That’s Already Drywalled?

Last Updated on September 18, 2023 by Web Operator

How To Insulate A Garage Ceiling

In many garages across the US, the roof space overhead is often overlooked. The insulation is not considered at all, let alone a ceiling. Often a garage that was previously used only for storage and/or parking cars becomes a place that the house residents hope to use as a livable part of the house.

While the ideal time to insulate a garage ceiling would be before the drywall ceiling is installed, it is possible to install insulation after drywalling without needing to remove the drywall. This is done with injection foam insulation, blow-in insulation, or installation from the attic above.

Whatever your reasons for needing to insulate your garage ceiling, there are several options available that will allow you to install the necessary insulation without the need to remove the drywall. Each option has its advantages and disadvantages, but they will all help to bring down your heating and cooling costs.

How To Insulate A Garage Ceiling Already Drywalled

How To Insulate A Garage Ceiling Already Drywalled

There are several reasons a homeowner might want to insulate their garage ceiling after drywalling.

  • Perhaps you’ve decided to turn your garage into a livable space for the rest of your house, or you simply want to prevent an uninsulated garage from causing havoc with the temperatures in the rest of the house.
  • Perhaps the attic space above your garage is suffering due to a lack of insulation below, creating a need for insulation in the garage ceiling.

Whatever the reason for installing insulation, several options are available to you. Firstly, the most logical option would be to install insulation on top of the drywalling. This is done from the attic space above the garage. 

This is the easiest option because almost any type of insulation can be used. There is no requirement to create any holes in the drywalling that need patching up afterward. Naturally, this method can only be used if it’s possible to access the space above the ceiling.

The next method to be discussed is using injected foam insulation to fill the gaps between the rafters. This is done simply by drilling holes in the drywall, inserting a hose into the hole, and filling up the cavity between the drywalling and the joists.

The third alternative is to make use of blow-in insulation. This is usually loose-fill fiberglass or cellulose insulation blown into the joist cavities, filling up all the gaps to create a well-insulated ceiling.

A few other alternatives exist, including the installation of rigid foam board insulation on top of the existing wall before installing timber boards over the top or installing plasterboard over the existing drywall. These methods tend to reduce the ceiling height and may not necessarily pose a long-term solution, so it’s important to bear these facts in mind.

Insulating From Above

The first method of insulating a garage ceiling that has already been drywalled is by far the simplest. It requires, however, that the space above the ceiling of your garage is not only accessible but large enough for a human to enter it in order to conduct work.

If the space above your garage ceiling meets the above-stipulated criteria, you can go ahead and install the insulation of your choice. Loose-fill insulation such as cellulose is an effective option here. This type of insulation is sold in large bags, and all you need to do is lay it in all the spaces between the joists on top of the ceiling that has already been installed.

Ensure that the loose insulation fills every nook and cranny, but be sure not to compact it. It tends to do a better job of insulating when air is able to move around it more effectively. The height of the insulation should be between ten and twelve inches overall.

Batt or roll insulation is another good option and is usually made of fiberglass, cotton, or wool. These rolls of insulation can be laid either between the ceiling joists or over the top of them. They can also be placed over any existing loose-fill insulation.

Injection Foam Insulation

Injection Foam Insulation

Injection Foam Insulation is highly effective at insulating above a ceiling that has already been drywalled. In order to install it, holes are drilled through the drywall into the cavities between the joists. It’s important that you locate all of the joists using a stud finder to ensure that no cavities are missed.

A hole is drilled into each cavity, and the injection foam is simply pumped through the holes, filling up the entire cavity before the hole is sealed off and repaired. The biggest benefit of this type of insulation is that it fills every crevice above the ceiling, ensuring there are no openings for hot air to escape or for cold air to enter.

Blown-In Insulation 

cellulose insulation

Blown-in insulation is manufactured using the same materials as conventional insulation batts or rolls. The main difference is the form in which they come, being loose as opposed to being formed into rolls.

Cellulose insulation is generally made using recycled paper products, while fiberglass wool is simply made from glass fibers. Mineral wool, on the other hand, is made using blast iron slag.

The process of installing this type of insulation is simple. Simply buy as many bags as you need of the insulation, drill holes through the drywalling, and blow the loose form insulation into the cavities using a specially designed blower with a long hose.


Previously, you may have thought the only way to insulate your garage ceiling after drywalling has been installed is to rip out the drywalling, install the insulation, and then reinstall the drywalling afterward.

Fortunately, it is not necessary to go to these extents thanks to the methods described above. 

Whether you decide to opt for injected foam insulation, blown-in insulation, or any other applicable method, you can be assured of a successful insulation project that will assist in creating a livable space in your garage all year round.

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Barry Gray

Hi, I’m Barry. I’ve loved woodworking and bringing things back to life for more years than I care to remember. I hope my passion for tools comes across loud and clear in everything you read here on The Tool Square.