How to Insulate a Metal Shed [Best and Cheap Ways]

A metal shed is an excellent choice if you want a durable, maintenance-free solution for outdoor storage. My neighbor put one in his backyard a few years ago. He thought it would be a great place for a workshop. But when winter came, he realized that unless he wanted to freeze, he needed some insulation. The next step was to find out how to insulate a metal shed.

Metal sheds without any insulation amplify the exterior temperature. In Fall and Spring, warm days followed by cool nights results in condensation. Usually, this forms on the interior surfaces of the metal shed. Condensation means you will have water in your shed – not good! Properly insulated metal sheds negate this problem.

Insulating your metal shed is not difficult, but can be time-consuming, so plan on spending most of the day to do it right. Here’s how:

  • Measure the wall, ceiling, and floor area of your metal shed.
  • Remove internal wall sheathing, if necessary
  • Using closed-cell spray foam, coat the walls in 2-inch layers
  • Let the foam dry between layers
  • Apply closed-cell spray foam to ceiling in the same manner
  • Wait for the foam to dry
  • Lift shed to install rigid foam panels beneath the floor
  • OR, remove the floor to install rigid foam panels between joists
  • Re-install interior sheathing and flooring, if necessary

How to Insulate a Metal Shed

Reasons for Insulating a Metal Shed

Metal sheds are excellent thermal conductors. Unfortunately, good thermal conductivity is bad news if you want to have a dry shed. Why? Metal, much more than plastic or wood, absorbs the sun’s energy much more efficiently. Therefore, on a hot day, the inside of your metal shed will be much warmer than the inside of wood or plastic shed.

Condensation

So what if your shed is hot in the summer? When the shed heats up during the day, all of that heat wants to escape at night when the temperatures fall. Since metal is an excellent conductor of heat, it easily allows the internal heat of the shed to flee outside. When this happens, condensation forms on the interior of the walls and ceiling of the shed.

Since the moisture is too heavy for the external cold air of night, it forms condensation. If this happens night after night, you will find that the interior floor of your shed all around the base will have watermarks and, eventually, rust. It will even form on the ceiling and drop onto your floor. If you have a wood floor, this can cause rot and ruin the structural integrity of your metal shed.

Control Interior Temperature

Insulating your shed can reduce the amount of condensation on walls and ceilings. Limiting the heat transfer from the exterior walls to the interior will not only maintain a more comfortable interior temperature in summer but also reduce the amount of heat loss in the evening. Reducing heat loss in the interior means less condensation in the shed.

Another temperature control method is ensuring your metal shed has proper ventilation. Insulating in the summer has obvious benefits. In the winter it can keep you warmer if you have a small heater going inside. However, moisture from your body and the heater can get trapped in the metal shed and form condensation on your interior walls.

Adequate ventilation, such as a roof vent or vents in the gables of your shed are effective in removing moisture from the inside of the shed.

Acoustic Control

A metal shed is essentially a reinforced metal box that you store your equipment in. If you plan on having a workshop, music studio, or anything else that makes lots of noise in your metal shed, then be prepared for some seriously loud reverberations.

Operating a grinder or table saw in a non-insulated metal shed will not make you popular with the neighbors.

Therefore, insulation is a simple soundproofing solution. Whether you use fiberglass batts, rigid foam, or spray-foam, you can bank on your insulation dampening sounds coming from inside your metal shed.

Insulation Options for a Metal Shed

Insulating a metal shed is not much different than insulating any other type of shed. However, due to the thermal properties of metal versus wood or plastic, choosing the right insulation for a metal shed differs from insulating other types of sheds.

Fiberglass Batts

Fiberglass Batts insulationFiberglass batts are commonly used in metal sheds. Larger, prefabricated metal sheds sometimes come with fiberglass batt systems already installed. The prime advantage with fiberglass is that it offers good r-value, around R-13 for 4 inches while remaining inexpensive.

In a metal shed, moisture is the enemy. Fiberglass batts do not perform well when wet. Therefore, faced fiberglass batts that come in rolls are ideal. The faced part, whether vinyl, plastic, or even a paper composite, is perfect for sheds. The facing ensures moisture from the internal environment does not enter the fiberglass and ruin it’s R-value.

Some fiberglass batts are completely encapsulated by a plastic, vinyl, or other composite vapor barriers. These are more expensive, but also more resistant to moisture. This insulation rolls out and installs easily, and is highly durable. It works well on walls and ceilings.

Pros

  • Inexpensive
  • Easy to install
  • Good for walls and ceiling

Cons

  • Not moisture resistant
  • Faced batts are more expensive
  • Won’t work in sheds without studs

Rigid Foam Board

Metal shed insulationRigid foam board is another option for insulating a metal shed. However, many styles of the metal shed are not conducive to having foam board on the interior of the shed. Any shed with curved wall surfaces, such as a Quonset hut-style of a shed, will not readily accept a rigid piece of foam.

Many metal sheds have studs that are not the standard 16” or 24” apart. You may end up having to cut your foam many times to fit or double up pieces of foam to fit larger gaps. Either way, you will likely end up fitting foam into unusual-sized stud openings. While you can always tape seams and install a vapor barrier, gaps between foam panels will allow heat and moisture in and out.

Metal sheds without studs, like many of the prefabricated versions found in the parking lots of large home reno chains, don’t have any studs. In this case, installing a rigid foam board is a cheap alternative to using spray foam. Boards can be cut to fit the height of the shed, taped, and then another layer can go on top. Adhesive, strapping, or other fasteners can be used.

Rigid foam board is best used on the floor of a metal shed, where the foam can rest between the wood joists of the wood floor. If the floor is also metal, foam can still be used underneath the entire shed. Since foam has excellent moisture resistance, it is best used in shed floor insulating applications.

Pros

  • Excellent moisture resistance
  • Well suited to floor insulation
  • Offers decent R-value
  • Cheap alternative to spray foam

Cons

  • Cannot bend to fit curved surfaces
  • May not fit certain wall or ceiling cavities well

Spray Foam

Spray Foam InsulationSpray foam offers the advantage of being a vapor barrier along with having an extremely high R-value per inch rating. Closed-cell polyurethane spray foam effectively seals the inside of your shed from exterior thermal conduction and moisture.

Since this type of spray foam keeps moisture out, it can also keep it in during winter months if you heat your interior space or spend time in the shed. If that is the case, ventilating your shed is a must. Ventilation will remove excess moisture in your metal shed and keep the spray foam from getting condensation on the interior walls and ceiling.

Closed-cell polyurethane spray foam kits are available at most home renovation stores. They are quite expensive, but if you are doing it yourself, then you are halving your cost compared to hiring someone to spray for you. Simply spray onto the walls of the shed in 1-inch layers, and repeat the process on the ceiling.

Pros

  • Offers the best R-value
  • Also a vapor barrier

Cons

  • Lengthy application process
  • Expensive
  • Hard to remove once applied

Mineral Wool

Mineral Wool insulationSimilar in application to fiberglass batts, mineral fiber insulation also comes in batts for 4” and 6” wall stud applications. Mineral fiber has excellent moisture resistance. However, when in direct contact with moisture, it shrinks and loses it’s R-value.

Mineral fiber is made with various ingredients, such as crushed stone, so it is much easier to handle than fiberglass. Since this fiber is made up of molten rock, it is utterly fireproof although this might not be an issue with a metal shed.

Mineral fiber insulation does come in foil-faced versions, which are an option for metal shed use. However, they are more rigid than fiberglass faced and encapsulated insulation, making them more difficult to install in curved roofs or Quonset-style sheds. If your metal shed doesn’t have studs, then the application of this insulation is difficult.

Pros

  • Excellent R-value
  • Moisture, rodent, and fire-resistant
  • Easy to install

Cons

  • Faced products are expensive
  • Does not work well with curved shed structures
  • Difficult to apply in sheds without studs

Blown-in Cellulose

Cellulose Blow-in InsulationCellulose blow-in insulation is often a mixture of old newsprint, sawdust, or other paper waste products that are treated with fire-retardant chemicals. It offers a higher R-value than fiberglass and a similar R-value to mineral fiber. Since cellulose is a paper product, it is not completely fire or mold proof.

When installing blown-in cellulose in a metal shed, you must have some barrier affixed for the insulation to fall into. As well, your shed must have sheathing on the ceiling or a vapor barrier with an opening that allows you to fill it with cellulose.

Blown-in cellulose does have fire retardant chemicals; however, it is still a paper and wood product. Typically, paper and wood do not react well to moisture. Mold and reduced R-value are factors that make cellulose a less-viable option in a metal shed, even with a vapor barrier.

Pros

  • Offers higher R-value than fiberglass
  • Blown-in offers dense coverage

Cons

  • Difficult to apply
  • Not resistant to moisture, mold, or rodents
  • Needs a vapor barrier

What Is the Best Insulation for a Metal Building?

When choosing the right insulation for your metal shed, r-value and price are likely going to dictate what kind of insulation you put in your shed. As well, some insulation types require much more time and effort than others. Let’s take a look at how the various insulation types stack up against one another.

R-Value

The r-value of various insulation products varies depending on the specific brand, although we can still make fairly accurate assumptions on how well certain insulation can insulate a metal shed. Below, we’ll rank the insulation types based on r-value per inch of insulation thickness.

  1. Closed-cell spray foam – 7.0
  2. ISO rigid foam – 6
  3. Mineral fiber – 3.8
  4. Cellulose, blown-in – 3.5
  5. Fiberglass batts – 3.4

Price

All insulation products have many different brands to choose from, and not all are of the highest quality. We’ll take a look at the cost of various insulations using an average of R-13 per square foot.

Below is a ranking, from highest price to lowest, of the various insulation types you can use for your shed.

  1. Polyurethane closed-cell spray foam- $7.50/sq. Ft.
  2. ISO rigid foam- $1.20/sq. Ft.
  3. Mineral fiber- $0.55/sq. Ft.
  4. Blown-in Cellulose- $0.45/sq. Ft.
  5. Fiberglass batts- $0.40/sq. Ft.

Ease of Installation

Installation is another factor to consider, as some products may require special tools or safety equipment that will add to the cost of your project. While there is no concrete way to measure the easiest installation process, we can reasonably assume that rigid foam is the simplest and fastest installation method.

We’ll rank the ease of installation of all our insulation types, starting with the easiest first.

  1. ISO rigid foam – cutting foam to size is simple, although the rigidity makes getting a tight fit harder.
  2. Closed-cell spray foam – requiring special safety gear such as a suit and mask, closed-cell foam installation is labor-intensive. Once started; however, it applies quickly.
  3. Fiberglass batts – unfaced or faced batts sit between studs in the wall. If there are no studs, the installation gets tricky and you need to find fasteners to affix it to the walls.
  4. Mineral fiber – much like fiberglass, mineral fiber also sits between studs. Again, without studs, the application is difficult.
  5. Blown-in cellulose – less toxic than polyurethane closed-cell foam, loose cellulose is easy to apply. However, you need a barrier to ensure the loose-fill doesn’t spill onto your shed floor.

The Best Option for Insulating Metal Shed

Insulating Metal ShedClosed-cell spray foam is the best option for insulating your metal shed. It offers excellent R-value per inch, as it can achieve R-18 with little more than 3 inches of thickness. No other insulator can match that R-value, as mineral fiber, rigid foam, and fiberglass are all around R-13 for 4” walls.

Although you can purchase DIY closed-cell spray foam kits at your local home reno store, professional installation is best. These days, professional spray foam installation is much cheaper than in the past. Paying an expert to spray your metal shed with closed-cell foam will not break the bank.

DIY spray foam kits provide all the tools you need to complete the job. However, the applicators and nozzles often break, and many report having difficulty getting the right consistency of foam to come out of the applicator. Save yourself time and hassle and pay a professional. It might cost you $500 extra dollars, but the quality of the job will enhance the life of your metal shed.

Lastly, the application of spray foam on a clean surface is critical. Spray foam is ideal because of its coverage ability. It covers every last nook and cranny, keeping moisture and air out of your shed. Clean the wall surfaces completely and ensure they are dry before applying spray foam. If walls have any moisture, the spray foam can trap that moisture and rust can form on the interior or exterior shed surfaces.

Alternatives for Insulating Metal Shed

Rigid foam board is another excellent option, and cheaper than closed-cell spray foam. ISO rigid foam boards offer the highest R-value per inch of any other foam product such as EPS or XPS. Since all ISO foam insulation is faced, it is a vapor barrier. When using in a shed, this negates the need to purchase poly film or radiant barrier to act as a vapor barrier, reducing your cost.

ISO rigid foam is also very easy to handle. It cuts easily with a jigsaw, handsaw, or table saw and fits snugly between wall studs. Installation is quick once you have all your measurements, and the foam is very light and easy to handle.

If you don’t have studs in your shed, rigid foam still works well. You can affix the boards to the wall with strapping once applied, metal tape, adhesive, or other insulation fasteners. Boards are also conducive to layering, so you could use several layers of boards, overlapping gaps, for more insulation.

How to Insulate a Metal Shed

Insulating corrugated metal shed

Insulating a metal shed with spray foam requires a spray foam kit and safety gear such as a protective suit, mask, and respirator. Cleaning supplies to clean the inside walls of the shed are also a necessity. After cleaning, ensuring all surfaces are dry and free of debris will enable the foam to adhere without any water getting trapped underneath.

Here’s how to insulate a metal shed with closed-cell spray foam:

  1. Remove all items from your shed.
  2. Tape all windows, vents, outlets, switches and other openings with plastic.
  3. Wash down interior walls and ceiling, and then dry them thoroughly.
  4. Put on your safety gear, as per the directions on the spray foam kit.
  5. Spray the foam as directed. Start with the ceiling and work your way down to the bottom.
  6. If the shed has stud cavities, use a picture-frame pattern, filling in the middle of the cavity last.
  7. Ensure you do not spray more than 2” thick at a time. Doing more can pose a fire risk. Let the foam dry before attempting more layers.
  8. When done with the interior, you’ll want to insulate underneath your metal shed, if possible.
  9. Lift your shed, either with a jack or small tractor.
  10. Apply the spray foam in the same manner as you did on the interior. Again, make sure the bottom is clean and free of debris before application
  11. If you cannot access underneath your shed, remove the floor panels of your shed. If you have a backing underneath the entirety of the shed, you can spray between the joist cavities. If not, you’ll have to use rigid foam.

If spray foam is too expensive, the next best method would be ISO rigid foam boards to insulate the inside of your metal shed. Here’s how to insulate with ISO foam boards:

  1. Remove all items from the interior of your shed.
  2. Measure the area of the walls and ceiling. You want exact measurements as foam must fit snugly.
  3. Cut your foam board to fit stud cavities. If you don’t have studs, cut foam to stand vertically, fitting the height of your shed walls. Ensure the fit is tight, but not so tight that it distorts the shape of the foam. You can layer your foam as much as you want, but make sure additional layers are installed to offset foam board gaps. This ensures optimal insulation.
  4. Install foam in the ceiling. Cut foam pieces to fit tight between rafters. You can use construction adhesive or a strapping to affix foam board to the ceiling if there are no rafters.
  5. If you can access underneath your metal shed, measure the joist cavities. Cut foam to fit between joists. If there are no joists, lay the board down in an unbroken pattern to cover the entirety of the shed floor. Again, you can layer foam to improve the r-value.
  6. If you are unable to get under the shed, remove the floor of the shed. Install the rigid foam between the joist cavities. Alternatively, you can lay the foam over the joists in an unbroken fashion. If there are no joists put the foam board over the entire surface and re-install the flooring.

Conclusion

When installing insulation in your metal shed, remember that moisture is your number one enemy. Whether you use ISO rigid foam boards or spray foam, an appropriate vapor barrier and proper ventilation should always be in place.

When installing spray foam, ensure you follow all safety precautions as outlined in the directions of the kit. Although an effective product, spray foam has a host of chemicals that can damage your lungs and eyes. Use care when applying it yourself.

As always, thank you for taking the time to read this article on how to best insulate a metal shed. I hope it helps you when it is time for you to insulate your metal shed. If you have any questions or comments, please feel free to drop me a line, below.

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