How to Insulate a Shed (2024)

Project Overview

Working Time: 1 or 2 days
Total Time: 1 or 2 days
Skill Level: Beginner
Estimated Cost: Around $0.90 per square foot of fiberglass insulation, or $1.75 per square foot of mineral wool insulation

Before You Begin

Fiberglass insulation (and mineral wool insulation to some extent) can cause itchiness. Insulation manufacturers recommend covering up from head to toe and wearing gloves. Install insulation in a well-ventilated area, if you can. It’s a smart idea to wear a respirator, safety glasses, and a hat.

Make sure to leave plenty of room on the shed floor for cutting fiberglass rolls to shape. For small sheds, it’s usually easiest to remove everything from the shed before starting this project.

Measure the walls, ceiling, and/or floor, and get enough insulation before starting the project. Most of the best shed plans utilize 2×4 framing, so use insulation that fits in these stud bays (the packaging is clearly marked with sizes). Typically, the faced fiberglass insulation that fits in a 2×4 stud bay will offer an insulation value of R13. (R-value measures how well insulation works to keep heat from coming into, or escaping from, a space. Insulation manufacturer Johns Manville recommends that exterior walls have insulation with R-values between 13 and 23.)

Finally, note that the following steps are ordered for regions where it is cold outside during the winter. For warmer climates that require air conditioning most of the year, you’ll want to install the vapor barrier before the insulation.

Step 1: Calculate how much insulation you need.

Most rolled fiberglass insulation comes in 8-foot-long strips, each of which are designed to fit between a 16-inch or 24-inch stud bay. To determine how much insulation you need, count the number of stud bays and rafter bays in your shed, divide that number by the number of strips in the package, and round up.

You can also use continuous rolls of insulation, which produce less mess and waste. To determine how many continuous rolls you need:

1. Measure the height of a stud bay and multiply that number by the number of stud bays.
2. Measure the length of a rafter bay and multiply that number by the number of rafter bays.
3. Add these numbers together to get an overall length.
4. Since rolls of 2×4 insulation are typically around 32 feet long, divide your overall number by 32 and round up.

Step 2: Prepare the shed.

Empty the shed completely and perform an initial inspection. Look for any signs of damage or leaks. Make repairs now, before the insulation is installed.

This is also a good time to spray expanding foam around any windows, as well as caulk exterior gaps and seams. Pay attention to gaps around windows, vents, and other areas where rain or snow can penetrate seams or connection points and soak the insulation.

Step 3: Measure and cut the wall insulation.

Measure the height of the shed wall stud bays and add 1 inch to allow for a snug fit. Roll out the insulation on the floor, paper side up. In the case of mineral wool insulation, simply lay the 4-foot strips out. Transfer the measurement to the strip of insulation and mark the paper with a permanent marker.

Compress the insulation at this mark by laying a level across the strip and pushing downward. Once it’s compressed, cut along the edge of the level with a utility knife until the insulation is cut to length.

Note: If there are two or more people working together, one can continue cutting more insulation to length while the other begins installing what has already been cut. To ensure the cutter can make up for any irregularities in wall height, the person installing can double-check the height measurement every few stud bays. A two-person installation method can go quickly with mineral wool insulation, as each bay requires two strips stacked one on top of the other. The installer can place the bottom strip while the other cuts the top strip to length.

Step 4: Cut around obstructions.

Sheds with electrical outlets and windows will have plenty of small areas to insulate around. While it’s possible to stuff insulation around these objects, doing so compresses air gaps inside the insulation and prevents the insulation from doing its job. Instead, cut the insulation to shape around obstructions.

It’s often possible to trim the insulation in place. When it’s not, though, use a tape measure to find the position of the obstruction and transfer the measurements to a piece of insulation with a permanent marker. Use an insulation knife to cut any holes for the obstructions.

Step 5: Install the vapor barrier.

Once the insulation is in the stud bays, it’s time to install the shed’s vapor barrier. For paper-backed fiberglass, this simply requires overlapping the studs with the paper wings on either side of the strip and stapling them to the studs. This holds the insulation in place and also forms the vapor barrier.

Unfaced mineral wool insulation requires a plastic vapor barrier installed on the inside of the studs. Starting at the bottom, roll the plastic out onto each stud bay and staple the plastic in place. Once the entire bottom of the wall is covered with plastic, start another row overlapping with the bottom edge of the first row by at least 6 inches. Once the vapor barriers are in place, use seam tape to tape any edges.

Step 6: Measure and cut the ceiling insulation.

Repeat this process for the rafters. Measure from the shed’s peak to the edge of the wall’s top plate and add 1 inch. Cut the strips on the floor in the same manner as before. Once they’re cut to length, climb the ladder and install the end of the first strip in the low end of the rafter bay first, moving upward toward the peak. Staple the paper vapor barrier tabs onto the rafters along the way.

Mineral wool can get very crumbly and make insulating a shed roof challenging. It often makes sense to install a few scraps of plastic vapor barrier across the ends of the rafters and slide the mineral wool into place over top of it. It’s also a good idea to wear a hat and safety glasses while working overhead with any insulation product.

Step 7: Install the vapor barrier over the rafters.

Leaving the scrap vapor barrier pieces in place for Rockwool insulation, install the vapor barrier on top of the shed roof insulation. At the bottom of the rafters, start the next row so it overlaps the previous row by at least 6 inches. Be sure to tape any seams when done.

Installing a vapor barrier in a shed can be a tedious process because the collar ties or ceiling joists might get in the way. If it’s necessary to cut the vapor barrier around these objects, tape any seams or cuts created to make it fit properly.

Step 8: Insulate the shed doors.

Insulating shed doors is important, but it’s not easy with standard rolled fiberglass or Rockwool insulation. Use rigid foam board insulation, as it’s the easiest and best insulation for a shed door.

Measure each door’s width and height, and transfer those measurements to a piece of foam board insulation. Using the level as a straight edge, cut the foam board to size with the insulation knife. Take note of any latches or door hardware that you’ll need to cut around.

Once the foam board is cut, glue it to the back of the shed doors with foam adhesive. Finish the project by installing a door sweep on the shed door using a drill and the hardware supplied in the door sweep kit.

Final Thoughts

Insulating typical shed walls isn’t a difficult project, but it does take at least a full day of work to complete. After the insulation and vapor barrier is installed and sealed, it’s a good idea to install drywall or plywood over the insulation to protect it, as even the smallest poke can affect the insulation’s performance. Once it’s covered, though, the shed will be comfortable and ready for your office furniture, gym equipment, or storage items, and the interior space will benefit from better and more consistent temperature regulation.