How To Insulate A Garage Ceiling That Is Finished?

If you are setting out to heat or cool your garage, insulation is the first (and arguably the most important) step. Insulation does not work if it is not complete. You can have the best insulated garage floors and walls and roof in the world, but if you don’t insulate the ceiling, all of your expensive heat is going to rise into the rafters. If you haven’t insulated the roof, that heat will just escape into the great outdoors.

What If You Have A Finished Room Above The Garage?

What If You Have A Finished Room Above The Garage

Even if you have a finished and insulated room above your garage, you will lose heat from the garage unless you insulate the ceiling. Lack of insulation will make heating the garage more expensive in winter, and it will make cooling the room more expensive in summer.

For these reasons, garage ceiling insulation is very important in terms of energy efficiency.

Safety is another very good reason to insulate your garage ceiling if you have a room above. A garage that is used to park cars, work on painting products, store fertilizer, etc. presents a significant risk in terms of air quality.

When you seal the garage ceiling and the floor of the room above, you seal out potentially dangerous fumes, which might rise into the room above without good insulation.

What Kind Of Insulation Is Best For Garage Ceilings?


The most often used insulation for an unfinished garage ceiling is fiberglass, which is available in rolls or batts. Fiberglass roll can be cut to the sizes you desire. Fiberglass batt is precut.

To insulate your garage ceiling using fiberglass insulation, look for R30 or R38 value insulation. The R value identifies the thickness of the insulation.

The thicker the insulation, the higher the R value will be. You can determine exactly what thickness you need by measuring your garage ceiling joists.

If using this type of insulation, you should also check your local building codes to see if you need to get faced insulation or if it’s alright to use bare insulation. Faced insulation is the kind that has a paper or plastic cover on one side which works to repel moisture.

This is a bit safer and easier to work with, and it is required in some places. The facing works as a vapor barrier to protect the insulation against dampness.

Blown in insulation

If you have a finished garage ceiling, you may want to have loose cellulose (recycled, shredded, fire resistant paper) or loose fiberglass blown in.

This is done by making a series of small openings in the finished ceiling and simply blowing the material into the spaces between the ceiling and the roof or floor above.

Spray foam

Another option for insulating either an unfinished or a finished ceiling is closed cell spray foam. Expanding spray foam will swell to fill up any gaps, cracks and odd spaces behind walls and between ceilings and floors or rafters above.

This water resistant expanding spray can be used to insulate the undersides of unfinished roofs, walls and ceilings. It can also be sprayed into the cavity between the roof or floor and a finished ceiling, or between exterior walls and interior sheetrock. It’s also excellent for filling in the odd gap or crack.

What Kind Of Equipment Do You Need To Insulate A Garage Ceiling?

Before you begin your garage ceiling insulation project, assemble these tools:

  • Scaffolding to access pitched roof or ceiling
  • Ladder and step ladder
  • Tape measure
  • Vapor barrier
  • Staple gun
  • Box cutter

You’ll also need protective gear and clothing to keep dust out of your lungs and eyes and to prevent itchy skin if you are using fiberglass insulation.

Be sure to have:

  • Closed shoes or boots
  • Long sleeved shirt
  • Safety glasses
  • Long pants
  • High socks
  • Dust mask
  • Gloves

Note that it’s best to do this sort of job during cooler weather because of the comfort level factor.

How Do You Install Garage Ceiling Insulation?

Luckily, installing garage ceiling insulation is an easy task, and it won’t take long if you prepare well, assemble your materials and organize your equipment in advance. Here’s how:

  1. No matter what kind of insulation you decide to use, you can use expanding foam to seal up any holes and gaps. For this purpose, it can be purchased in spray cans from your local home improvement center or hardware store.
  2. Make sure you will have good ventilation. Before you start insulating, install roof vents and/or baffles as needed to make sure moisture doesn’t build up and cause mildew growth in your new insulation. Vents let fresh air in.

Baffles help prevent insulation from getting bunched up near the roof edges. Keep in mind that you’ll need to leave three inches of clearance for electrical fixtures and equipment, which need good ventilation to avoid overheating.

TIP: It’s a good idea to install baffles around these fixtures, and this is required in some locations.

How To Install Insulation Stops

You’ll also need to leave one inch gaps in the insulation to provide ventilation for any wiring that is present.

  1. If you have an unfinished garage ceiling, you can either install fiberglass roll or batt insulation from below and then cover it with drywall, or you can install the drywall and then blow in foam spray or loose fill fiberglass or cellulose insulation from above.

How Do You Insulate A Garage Ceiling That Is Finished?

There are a couple of ways to insulate a garage ceiling that is finished. If you want to use fiberglass roll or batt, you’ll have to insulate from above. If there is an attic space between the ceiling and the rafters, you can go in and lay the material down between the rafters.

Lay In Insulation

When you install fiberglass roll or batts from above, be careful not to damage the ceiling below. If you are laying the fiberglass directly onto sheetrock, naturally you will not want to walk on the sheetrock or put any weight on it as you will fall right through!

Take some half-inch thick sheets of plywood into the attic to lay between the joists so you can move around without having to perform a balancing act.

Cut the fiberglass batt or roll to exactly fit the spaces between the joists. Keep in mind that you’ll also need to leave three inches of clearance around electrical boxes, light fixtures, ducts, pipes and chimneys.

Anything that could get hot will need room to breathe. Leave an inch of space for wiring. Use baffles as needed or required. When you lay the insulation down, be sure to make it so that the paper or plastic facing is on the downside.

Insulate the inside of the trap door to the attic, too. You can lose a lot of heat through an uninsulated door.

Blow In Insulation

You could also blow in loose insulation from above. To blow cellulose or fiberglass into your finished garage ceiling, you can either do it yourself or hire a service. If you don’t have the equipment needed, it is readily available as a rental from most home improvement centers.

To blow in insulation from below, you could drill openings in the existing ceiling, blow the fill in from below and then reseal the holes. This is a good way to do it if there is a room above the garage. It’s easier and preferable to tearing up the floor of the room in order to insulate the ceiling.

Keep in mind that, no matter how you add insulation inside your ceiling, you have to leave space for electrical wiring and fixtures, ducts, pipes and chimneys and set up proper clearance for them.

To do this, you would install baffles in advance. Use caulking to seal the baffles up and keep insulation out. For very high heat areas, like chimneys, surround them with sheet metal to prevent creating a fire hazard.

What If You Don’t Want To Tear Up Anything?

If you are renting, or you simply don’t have the ability or the desire to tear up floors or drill holes in the ceiling, there are a couple of simple fixes.

  1. Seal gaps. If you have a room above your garage, you can make it safer by filling in any gaps with foam spray.
  2. Add a layer of insulation by adding carpet pad, carpeting and rugs in the room above the garage.
  3. Below, on the ceiling of the garage, you can easily and affordably add foil bubble wrap insulation using a staple gun and/or two-sided foam tape. Seal the seams with contractor grade aluminum foil tape.

These are simple, affordable fixes that almost anyone can do. If you are renting, you can take your floor coverings with you when you move on. Foil bubble wrap insulation is a little bit of an investment, but it will save you lots of money in heating and cooling costs.

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