Stapling Insulation To Garage Roof Trusses Energy Conservation:

Installing Fiberglass Insulation
In A Garage Ceiling

In This Article:

Fiberglass insulation is cut to length, placed between roof trusses and stapled to the framing. Insulation is notched around electrical boxes. Also: Some thoughts on heating a garage workshop.

Related Articles:
Skill Level: 2 (Basic) Time Taken: About 12 Hours

By , Editor


My garage is used for more than just parking cars. I work in my garage: car repairs, carpentry, welding, and much more. Working in a cold garage in the winter is downright unpleasant. An ideal garage workshop would be finished, insulated and heated.

But I'm not there yet. My garage needs some structural changes before I'm ready to do the interior finishing. I didn't want to spend another winter with an ice-cold garage, so I decided to make the one change that makes the greatest difference.

I discovered years ago that merely insulating the ceiling in a garage makes a HUGE reduction in heat loss. Before insulating the ceiling in this garage, I could run a kerosene heater with an output of 23,000 BTU's per hour and the temperature would increase by 3 or 4 degrees. After insulating the ceiling I found that the same heater would raise the temperature by 20 to 25 degrees.

The house I bought recently has a 24' x 24' detached garage with trusses spaced 24 inches on center.

There were 12 truss spaces or "bays" to fill with insulation.

Roof trusses before insulating garage.


When I began taking pictures, I had installed fiberglass just over halfway across the ceiling.


I used R11 kraft-faced fiberglass insulation in a roll, rather than pre-cut batts. The roll was about 70 feet long, and I needed about 24 feet for each bay. Each roll gave me strips of insulation that completely filled two bays and almost filled a third. The insulation I used was 23 inches wide, which fits snugly in the 22½" space between trusses.

When the trusses or ceiling joists are spaced 16 inches on center, I buy 15" wide insulation.

R-11 Fiberglass insulation, kraft-faced, 23" wide.


Cutting Fiberglass Rolls The Easy Way:

Since I didn't have a helper for this project, I figured that trying to handle 24 foot lengths of fiberglass would be kinda difficult. So I cut the insulation into 12 foot lengths.

To cut the insulation without having to measure every time, I made a mark by applying some duct tape to the floor (red arrows). I made the left edge of the tape about 12 foot 2 inches from the garage door. Experience has taught me that it's better to cut the insulation a bit long when insulating ceiling bays, because the fiberglass can overhang at the ends a little. Easy way to make repetitive cuts in roll of fiberglass insulation.


Cutting fiberglass insulation with a knife and ruler. I placed a scrap of plywood over the duct tape to act as a cutting board.

Then I just laid a 2-foot straightedge across the fiberglass and made a cut with a sharp knife.

I used one of those box-cutter knives with the blade extended about two inches.


One problem with roof trusses is that the bottom chords tend to flex side-to-side, so the distance between adjacent trusses isn't always 22½".

Consequently, the 23" wide fiberglass kept falling out before I could staple it in place.


After some very frustrating wrestling with long pieces of fiberglass, I figured out an easy way to support the insulation while I fastened it.

I clamped 4 or 5 bar clamps just above the lower edge of the bottom chord. These were inexpensive 24" bar clamps that I bought at Big Lots.

Quick-Grip clamps would work too, but bar clamps hold better.

Draping fiberglass over bar clamps to hold it up. Then I simply threaded the piece of insulation over the bar clamps.

I found it easiest to start in the middle of the group of clamps,  thread half of the material to one side, then thread the other end of the fiberglass over the remaining clamps (in this case, the clamps to my right).


After a few minutes I had the 12-foot length of insulation resting close to its final location.

Note the spacing of the clamps... these were about 2 to 2½ feet apart.

Using bar clamps to support fiberglass before stapling.


Then I began stapling the paper flaps to the bottom surface of the trusses.

I started at the wall, drove in a few staples, and then tugged on the insulation to pull it tight. With one hand tugging on the fiberglass, I stapled the flaps with my other hand.


It really helped to have an electric staple gun, since I could reach my arm out and easily drive a staple.

With a manual staple gun I would need to get my body beneath the tool to drive a staple, which means that I would have to move the ladder, stool or scaffolding that I used to reach the ceiling.


By the way... this is the rolling scaffold that I used to reach the ceiling. This thing is about 4 feet  long, so I was able to reach a sizable area before I had to move the scaffold.


The insulation had been stapled about 2 feet out from the wall. Notice how the kraft paper facing is smoother where it had been been pulled tight and fastened.


Stapling fiberglass R11 insulation to ceiling while pulling taut. This is another picture of me tugging on the insulation with one hand and stapling with the other.

When I had stapled up to a bar clamp, I removed the clamp and set it aside.

(Yeah, I know... I should be wearing eye protection, but they fog up when I'm wearing a dust mask.)

Wearing a dust mask is a good idea when working with fiberglass insulation because you will be breathing in tiny strands of glass fibers that float in the air. I find these glass fibers really irritate my nose and throat.

Here I'm stapling the the end of the first piece of insulation to be installed in that truss bay.

I started the next piece of fiberglass at this point and worked toward the other end of the garage.

As I mentioned earlier, I cut each piece of insulation half the length of the garage.

Why? Because a full-length piece is too difficult to handle. Also, cutting full-length pieces on the garage floor would have been a major hassle because the garage has too much stuff in it. If I had been doing this job in the summertime, I could have opened the garage door and unrolled the insulation from some point in the driveway and still made the cut on the garage floor.


The Proper Way To Staple
Kraft-Faced Fiberglass Insulation:

The Wrong Way (Sort Of):

When I stapled the paper flaps to the trusses, I folded the flaps over the face of the 2x4. BUT... this is NOT the proper way to fasten kraft-faced fiberglass insulation.

The problem with this method is that drywall cannot be glued to the framing, which most drywall hangers prefer to do.

I used this fastening method because when I do the interior finishing on this garage I will be screwing OSB (oriented strand board) to the ceiling, with no adhesive.

Alternative method of stapling fiberglass, not usually done.
I have also used this method when I am going to install rigid foam insulation over the studs before hanging the drywall.


Proper method of stapling fiberglass insulation to framing.

The Right Way:

The method recommended by insulation manufacturers is to staple the flap to the side of the stud, joist or truss. The red arrow shows where the staples go.

As you can see, the insulation can get crushed at the edges, and the R-value will be reduced slightly there.


Small Problems:

When I reached the wall, there was no easy way to complete the installation without gaps.

Note that the fiberglass extends above the wall far enough to reach the outside edge of the studs.


I tried pulling the insulation down, but it was impossible to make it lie flat with no gaps between the top plate and the fiberglass.


My Solution:

I used a stick of wood about 2 feet long to reach above the insulation and tap the fiberglass down against the top plate.

Coaxing fiberglass insulation to lay flat at wall.


Don't Forget Attic Access:

Before I started insulating the ceiling, I framed in a basic attic access hatch. I just fastened a couple of 22½" long 2x4's between the trusses. I spaced these boards about 4 feet apart so I could make an attic access hatch 4 feet long by  22½" inches wide. But I haven't built this attic access hatch yet, so I just stapled a piece of fiberglass over the access hole, for now.


Cutting Around Electrical Boxes:

Perhaps the greatest nuisance of installing fiberglass insulation is the need to cut the material around electrical boxes. Attention to detail is important here, because sloppy cut-outs will allow warm air to escape... this is important when insulating walls but doubly important when insulating the ceiling.

Cutting insulation around electrical boxes. I use ordinary scissors to cut fiberglass around junction boxes.

First I made a "plunge cut" just above the box, parallel to the long side. I snipped the paper first and then cut all the way through the fiberglass strands.


Then I snipped the insulation between my parallel cut and the edge. It's hard to tell if I've cut all the way through, so I usually cut repeatedly until I can't feel any more material being cut.

Then I removed the cut-out piece.

Using scissors to cut fiberglass insulation around outlets.


Next I pulled the insulation down around the electrical box and fastened the paper tabs to the framing.

I made the cut-outs about ¼" smaller than the J-box so the insulation fit snugly.

After I was done insulating this ceiling, I realized something... I should have placed a scrap of fiberglass directly above each electrical box. Each box has NO insulation directly behind it, so all of these outlets (there are 9 of them) are points where heat can escape easily.

In case you're wondering why there are outlets in the ceiling... I wired a series of outlets to a switch by the door, and then I plugged my shop lights into this network of switched outlets so all the lights can be turned on with the flip of a switch.


The completed insulation job.

Even though this insulation has an R-value of 11, which is pitifully low for Northern Michigan, when I run a heater in my garage I can raise the temperature to a comfortable level within an hour or so.

Fiberglass insulation installed in garage ceiling.

After I install OSB on the ceiling I plan on adding 4 to 6 inches of blown-in cellulose insulation above this fiberglass. I did this with my last garage, (which had insulated garage doors and R-13 in the walls) and my 23,000 BTUh kerosene heater could add easily maintain a temperature of 50 to 60 degrees higher than the outdoor temperature.


Some Thoughts On Heating A Garage Workshop:

Kerosene Heater and Circulating Fan This is the 23,000 BTU per hour kerosene heater that I mentioned earlier. I also use a large circulating fan, pointed straight up, to stir up the air. Without the fan, the air near the ceiling gets quite warm while the floor remains stone cold.

One drawback of kerosene heaters is that when ignited it takes a couple of minutes for the flame to reach full strength, and during this time they give off smoke and a nasty smell. They also stink when the flame is extinguished.

I light the kerosene heater outdoors, or (if it's windy) at least open all the doors so the smell doesn't linger inside.

I recently bought this 15,000 BTUh heater that mounts on an ordinary 20 pound propane tank. I like this heater because it only takes about 15 seconds to reach its full glowing-orange output. There is no foul odor when starting or extinguishing this heater.

But... propane bought by the small tankful is about 25% more expensive than kerosene, when the cost per unit of heat is calculated.

The best long-term solution is to install a small, reasonably efficient natural gas heater, which would cost about 60% less than kerosene. Eventually I will run a gas line to the garage and have a heater installed.

Propane heater that mounts on 20 lb. propane tank.


More Info:

Tools Used:

  • Sharp Knife
  • Scissors
  • Tape Measure
  • 2-Foot Straightedge
  • Electric Staple Gun
  • Rolling Scaffold
  • Bar Clamps, 24" (4 to 5)
  • Work Gloves
  • Dust Mask

Materials Used:

  • R-11 Fiberglass Insulation, 23" Wide
  • Staples, 1/4" Long
Related Articles:




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Written January 6, 2008