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How To Insulate Garage Ceiling Rafter?

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If you’re using your garage as a space that is allocated for other activities apart from parking your car such as carpentry or, working on music, then insulate garage ceiling rafter should be your top priority. Your space will be more comfortable and energy-efficient.

Fiberglass insulation is the most popular choice when insulating garage ceiling rafters because it is effective at preventing heat loss and easy to install. On the other hand, spray foam insulation is the most efficient type against sound, heat, and moisture.

How do you Insulate Garage Ceiling Rafters

How do you Insulate Garage Ceiling Rafters?

Before we get into details about installing your ceiling rafter, it is essential to decide which type of insulation you’ll need depending on:

  1. Climate you live in
  2. The current condition of your ceiling rafters i.e finished or unfinished
  3. Type of insulation

Different types of insulation available

When it comes to insulation, there are four main types you can choose from:

Fibreglass Insulation

Fiberglass insulation is made of glass wool. It is the most popular choice for insulating garage ceilings and walls. It comes in rolls or batts that can be easily installed.

It is relatively inexpensive, fire-resistant, and very effective at preventing heat loss. Installation is straightforward and can be done by a beginner with no prior knowledge.

KEEP IN MIND: It can be a bit itchy for your skin.

Rigid Foam Insulation

Rigid foam insulation is made of polystyrene. It comes in boards that can be easily cut to fit between ceiling joists so overall installation is even easier compared to Fibreglass.

With its expensive price tag and not as effective sound-absorbing capabilities as fiberglass is a bit less popular.

Spray Foam Insulation

Spray foam insulation is made of polyurethane. It comes in a can that can be easily sprayed between ceiling joists. This type of insulation is fire-resistant, very effective at preventing heat loss, and with high sound absorbance.

NOTE: It is the most expensive type of insulation but on the other hand the most effective one.

Cellulose Insulation

Cellulose insulation is made of recycled paper. It comes in a loose-fill form. It is the most environmentally friendly insulation, but it is not as effective at preventing heat loss as fiberglass or spray foam insulation.

NOTE: You'll need a blower and a hose to install cellulose insulation.

What Tools & Supplies Do I Need?

You’ll need the following tools to get the job done:

  • Tape measure
  • Utility knife
  • Stapler Gun and Staples
  • Screw gun
  • Caulking gun
  • Step ladder
  • Mask
  • Gloves
  • Goggles
  • Air vents
  • Insulation material

Steps to Insulating your garage ceiling rafters

Installing insulation is easy. It also depends on the type of insulation you’ll be using. According to industry experts, fiberglass insulation is the best way for a DIY project.

1. Measure the space

It is important to measure the ceiling space before installing insulation to ensure that you get the right amount and type of insulation. Measuring the space also helps in for planning purposes.

Measure the width and height of the space to calculate the exact amount of insulation you will need.

TIP: Order around 5% more insulation than measured so you won’t have to hold the project and order again if you used it all. Additionally, you can always return unused back to your store.

2. Check for cracks or holes

It is important to check the ceiling for any cracks or holes. If you find any, you will need to fix them before installing insulation. Possible water leaks can damage it and cause mold to grow.

The easiest method is to use special gaps and cracks sealant for insulation. It will fill up any cracks up to 3″ wide.

Pro Tip: If you already have mold and mildew present, you can use bleach to kill it. Mix one part bleach with three parts water then apply it to the molds using a brush or a spray bottle. Let the solution sit for about 10 minutes and then rinse it off with water.

3. Install air vents

This is important because air vents prevent the accumulation of moisture, which can cause mold to grow. It is also important to install them in the ceiling of a garage to prevent heat from building up.

  1. Measure the distance between the two joists and cut the vent to that size. You can use a hacksaw.
  2. Drill a hole in the center of the vent. The hole should be big enough for the screw to fit through.
  3. Attach the vent to the joist using a screw gun. If you are using metal brackets, you can also attach them to the joist using screws.

4. Cut and install insulation

If you are using batts, cut them to size with a utility knife. Make sure that the batts fit snugly between the joists. When using loose-fill insulation, fluff it up with your hands before placing it in the cavity.

Once the insulation is in place, use a stapler to secure it to the joists. Make sure that the staples are spaced evenly so that the insulation is secure.

TIP: If you are using batts, you can also install them perpendicular to the joists. This will create a tighter fit and prevent the insulation from falling.

For those, who like to visualize everything, this video explains the above-mentioned steps:

5. Install drywall to give a finished look

You can install drywall to give your garage ceiling a more refined look, once the insulation is in place. Make sure that the drywall is flush with the edges of the insulation.

Once the drywall is in place, you can prime and paint it to match the rest of your garage. Besides the clean look, It will add additional protection against moisture and dirt.

How to install insulation in finished ceiling rafters?

The best type of insulation for finished ceilings is blow-in or cellulose insulation. It is highly efficient because it fills all the spaces and does not leave any gaps.

  • To install blow-in insulation, you first need to find the studs in the ceiling. You can do this by tapping on the ceiling with your knuckles. The studs are the joists that support the ceiling.
  • Once you have found the studs, use a drill to make a hole in the center of each one. The hole should be big enough for the insulation to fit through.
  • Then, use a blower to blow the insulation into the holes. Make sure that the insulation is evenly distributed between the studs.
  • If you are using cellulose insulation, you will need to wet it down before blowing it in. This will make it easier to blow in and will help it to stick to the sides of the studs.

If you are a visual person, watch the video below for easy instructions.

You could also install fiberglass insulation if you want to avoid using blow-in insulation. The installation process is quite similar to the finished ceiling, except that you have to reverse the insulation to the back of the ceiling or attic instead of the front.

Difference Between Rafters and Trusses

Rafters are more common in newer homes and a better choice for insulation because you can insulate the spaces between the beams and make them tight.

If you have a truss ceiling, you can still install insulation. However, it is a little more difficult because there are no spaces between the trusses for insulation itself. You will have to drill holes in the trusses and then blow them into the holes.

Another option to think about for truss ceilings is rigid foam. These foam boards glue directly to the trusses and cover with drywall afterward.

What type of insulation is best for my garage ceiling?

The type of insulation you need depends on the type of ceiling you have in your garage. If you have rafters, then you can use fiberglass or blow-in insulation. If you have trusses, then you will need to use a different type of insulation such as rigid foam or spray foam insulation.

To further make it easy for you, I have done the research and shortlisted Best fiberglass and styrofoam insulation for you.

JOHNS MANVILLE Fiberglass Insulation

You’ll love the savings you see on your energy bill each month after installing this fiberglass insulation. It will make sure your home is warm in the winter and cool in the summer. Because its formaldehyde-free, you can rest easy knowing it will be safe for your family and your home.

Johns Manville insulation is available in a variety of R-values (11-38), so you can find the perfect product for your needs. We featured R19 because we believe it offers the best combination of affordability and thermal resistance.


  • Reduce noise
  • R-rated – Availalabe in variety of R-Values (R11-R38)
  • Keep garage warm in winter and cool in summer
  • Easy to install
  • No itching
  • Affordable and top quality
  • formaldehyde-free


  • Has printed paper on the side

Styrofoam Rigid Insulation Foam Boards

Styrofoam Insulation is the perfect way to keep your home comfortable all year round. We especially loved how Styrofoam board technology provides superior thermal, moisture, air and vapour performance, making sure your home is well insulated all year round.

These insulation foam boards are a great way to insulate your garage attic and joists as they are sturdy enough to support your ceiling rafters. Additionally, they are versatile, you can use them in a variety of DIY home projects.


  • Versatile
  • Easy to install
  • Sturdy and durable – does not crumble or make a mess
  • Reasonable price
  • Excellent thermal insulation
  • No sagging – good resistance to moisture
  • Fire resistance
  • Made in the USA


  • Only 1 inch thick
  • A bit difficult to cut

What are the benefits to insulate garage ceiling?

Insulation of a garage ceiling is quite common in America because of these added benefits:

Sound Dampening

One of the main benefits of insulating your garage ceiling is that it can help to reduce noise. This is especially beneficial if you use your garage as a workshop or for other loud activities.

Temperature Control

Insulating your garage ceiling will also help keep the inside temperature consistent. This will lead to reduced bills. Moreover, if you’re storing valuable items, insulation will protect them from extreme temperature changes.

Fire Prevention

Another important benefit of insulating your garage ceiling is fire prevention. When the insulation is installed properly, it will prevent fire to spread.

Protection Against Carbon Monoxide

Insulating your garage ceiling can also help to protect you from carbon monoxide poisoning. The insulation will help keep the garage sealed off from the rest of the house and protect you and your family from inhaling the lethal carbon monoxide.

Increase in Home Value

Insulation will increase your home’s value significantly. This is because potential buyers will see it as a bonus and be willing to pay more for the property.

What R-value insulation should I use in my garage?

The R-value of insulation is the measure of its ability to resist heat flow. The higher the R-value, the better the insulation resisting heat flow. To determine what value you need, you will first need to know how much insulation your garage ceiling can hold. Most homes have between R-13 and R-38 insulation in their ceilings. If you do

What does it cost to insulate a garage ceiling?

The cost of insulating a garage ceiling will depend on the size of the garage and the R-value of the insulation. Typically, the average cost to insulate a garage ceiling with fiberglass batt is between $1 and $2 per square foot.

Do you need a vapor barrier when insulating a garage?

A vapor barrier is not always necessary when insulating a garage. However, if your garage is not properly sealed, it may be beneficial to install a vapor barrier to prevent moisture from entering the insulation.

What kind of insulation is best for garage rafters?

The most common type of insulation is fiberglass insulation. This type of insulation is inexpensive and easy to install. Another option is spray foam insulation. Spray foam insulation is more expensive but it will provide a better seal against air, sound and moisture.

Do I need to insulate my garage door or should I leave it?

It is not necessary to insulate your garage door. However, if you want to keep adequate temperature control in your garage, it is recommended to order a pre-insulated type. Keep in mind that insulated garage doors are quite expensive.