How to Insulate a Metal Roof: Step-by-Step

If you have a metal roof or you’re planning to have one installed, insulation is an important part of keeping your home comfortable and energy efficient. (Incidentally, here at Erie Home, all our metal roofs are insulated.)

A Beautiful Erie Home Metal Roof featuring a Timberwood Roof

While we recommend trusting a professional roofer to manage this type of upgrade, we realize there are some very handy and experienced homeowners who like to DIY their home improvement projects. If you’re installing your roof yourself or want to add to or replace the existing insulation, we’ve compiled all the information you need to insulate a metal roof.

Why Do You Need to Insulate a Metal Roof?

Before you do anything, it’s important to understand why insulation matters. The first is comfort; when you insulate your metal roof, there will be less heat transfer between the inside and outside of the house.

This is important, as it helps to keep the heat inside the home or prevent the heat outside from getting in.

For example, when you’re running your heat in the winter, and your home is nice and toasty, you want to keep that heat inside. However, during the summer, once your AC has cooled your home and it’s 90 or 100 degrees outside, you don’t want that heat coming into your home.

A well-insulated roof will keep hot air in or out, depending on the season. This will make your home more comfortable and improve energy efficiency since you won’t need to run the heat or air conditioning as much. As a result, you’ll enjoy lower utility bills.

Good insulation will also keep condensation at bay. Since metal roofs can be a place where moisture accumulates, you’ll want that insulation to help prevent the temperature extremes that lead to excess condensation.

The Best Insulation for Metal Roofs

If you’re having your metal roof installed, the installers (or you, if you’re doing it yourself) can install rigid board insulation. The boards are made of polyurethane or polystyrene, and they fit together tightly between the roof and the roof deck.

If you’re applying insulation from your attic, you’ll use either fiberglass insulation or spray foam insulation. Fiberglass is less expensive and can be cut to your needs, but because it sheds tiny shards of glass, it can be dangerous to use without the proper protective equipment.

Spray foam is more energy-efficient but more expensive than fiberglass, and it can be tricky to install.

How to Insulate a Metal Roof: Step-by-Step

Unless you’re installing your new metal roof yourself, you won’t be able to install rigid board insulation on your own, so we’ll focus on fiberglass and spray foam insulation here.

The preliminary steps are the same, but depending on the specific type of insulation you’re using, you’ll need to refer to the manufacturer’s instructions.

  1. Gather your materials. In addition to the insulation itself, you’ll need other materials to protect your surfaces and keep the insulation in place.

For fiberglass, you’ll need staples, a utility knife for cutting the insulation, and scissors.

If you’re using spray foam, you’ll need the spray gun and hoses, drop cloths to protect the attic floor and anything else you have stored nearby, sealant to fill the gaps, and a foam applicator cleaner to keep the spray gun and hoses clean.

  1. Gather your personal protective equipment. This is essential because fiberglass contains microscopic pieces of glass that can get into your lungs and irritate your skin.

For this type of insulation, you’ll need to wear long sleeves, long pants tucked into socks, a hat, and a face mask to keep your airways clear.

If you’re using spray foam, you should wear something similar and might also want to wear a disposable suit to protect your clothing.

  1. Prepare your workspace. Clear out any items from your attic and open any vents or windows for good ventilation. This is a good time to check the underside of the roof for any moisture or leaks.

Lastly, if you don’t have a solid floor, lay down plywood so you can work safely.

  1. Install the insulation, following the instructions on the packaging. If you’re using fiberglass, you’ll cut the batts to size and place them between the rafters, being careful not to push hard on the insulation.

If you’re using spray foam, you’ll be aiming for even coverage.

  1. Seal any air leaks. Once the insulation is in, check it to see if there are any gaps or openings where air can seep in. Use caulking or more spray foam around any pipes, ducts, or ceiling fixtures.

Final Thoughts

Installing insulation for a metal roof can be tricky, so if you’re not experienced using these types of materials, we highly recommend you consult a professional. Having a professional roofing company like Erie Home install your insulation minimizes the risks of using fiberglass or spray foam. We’re also adept at sealing all air leaks and making sure everything is installed securely.

Contact Erie Home today at 1-800-862-6400 to learn more and to schedule a free consultation and estimate.

Frequently Asked Questions

What is the R-value of a metal roof?

The R-value stands for the resistance value. It measures how effectively a material prevents heat transfer. A bare metal roof has little to no R-value because metal conducts heat very well.

However, once you add insulation, the R-value will increase depending on what you’re using. If you live in a tropical climate, you’ll want an R-value of around 38; for the rest of the country, an R-value of 30 is usually sufficient.

What is the best way to insulate a roof?

The best way to insulate a roof depends on the type of roof, climate, and your specific needs. For pitched roofs, commonly used insulation materials include batts and rolls, rigid foam boards, and spray foam.

Batts made of fiberglass or mineral wool are easy to install between rafters. Rigid foam boards provide high insulation values with less thickness, while spray foam offers excellent air sealing and high R-values.

For flat roofs, rigid foam boards are often used above the roof deck, or a spray foam insulation can be applied directly on the roof surface under a protective layer. It’s essential to consider factors such as the insulation material’s R-value (its resistance to heat flow), moisture control, and ventilation needs to achieve the best performance.

Do you need an air gap between roof and insulation?

Yes, in many cases, an air gap between the roof and insulation is necessary to prevent condensation and ensure the roof structure’s longevity. This gap, known as a ventilation gap, allows for air circulation, helping to keep the roof deck dry and prevent moisture accumulation that could lead to mold growth and structural damage.

The specific need for an air gap and its optimal size can depend on the type of insulation, roofing material, and the climate.

What’s the cheapest way to insulate a metal roof?

The least expensive insulation type is usually fiberglass.

Can you put too much insulation in a roof?

Yes. Depending on where you live, you’ll want an R-value of between 30 and 38. If you use more insulation than required, you could end up with too much humidity and moisture, which can lead to mold growth and excessive condensation.

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