Metal roofing offers many advantages. It’s incredibly durable and long-lasting. It’s one of the greenest solutions on the market, and it’s aesthetically pleasing. With all of that said, high thermal conductivity can be problematic when insulation isn't included in the building design.
An effective insulation strategy stops heat transfer, but it does far more than that. Insulation is also very effective at reducing noise during heavy rain, hail, and even extreme wind. Proper insulation with vapor barriers also reduces moisture. Eliminating moisture is key to decreasing a number of common roofing problems.
When it comes to insulation for metal roofs, there are a large number of options available. We'll look at a few of the most common in this post.
Fiberglass batt insulation is one of the more popular types for roofing. It’s relatively inexpensive and available in a wide variety of different R-values. In case you’re not familiar, R-value determines thermal resistance. The higher the R-value, the more insulating the material is. Variable R-value is key because different climates need different levels of insulation.
Should you insulate your metal roof with fiberglass batts? If budget is a concern, fiberglass batts can be a great option as they are the least expensive. On the flip side, batts come with a number of challenges. First, the batts can’t easily be shaped around the corners, rafters, and wires you’ll find near your roof. Second, they aren’t particularly good vapor barriers.
The consequence of this is that if the batts become moist, and the moisture isn’t dissipated, they can essentially lose their entire R-value. Professional installation can decrease the risk of this, as they can install moisture barriers and ensure that airflow allows for moisture dissipation. Nonetheless, professional consensus these days is that batts are no longer the most effective form of insulation for metal roofs.
If you do decide to move forward with batt insulation, be cautious. Fiberglass insulation is basically tiny shards of glass and you don’t want to breathe it in. Get appropriate PPE, or play it very safe and hire a professional installer.
Rigid Foam Board
Rigid foam board is more expensive than batt insulation, but for good reason because the R-values of foam board are much higher. This is an exterior roofing insulation option (don’t worry, it won’t be placed on top of the metal roof). It’s quite good at soundproofing, and it’s one of the best insulators on the market.
Some of the problems you see in fiberglass batts also exist here. Because it's rigid, it’s not easy to move around tight corners or awkward areas. Fortunately, as it’s an exterior insulation option, these problems usually don’t come into play, as the roofing will be placed directly over the insulation.
Note that moisture control is absolutely essential with rigid foam board insulation. Your roof will need to be vented to allow for airflow (and thus moisture control). You’ll also need to apply a vapor barrier, which is simple enough to do.
Spray Foam Insulation
Spray foam insulation is, again, more expensive than fiberglass batts. It also tends to have a lower R-value per inch than rigid foam. But if you’re dealing with a project that requires complete insulation, spray foam can be a great option.
As mentioned earlier, Rigid foam boards can be tough to install unless you’re installing a whole new roof because they don’t weave around tight corners and wires. Spray foam, on the other hand, can be sprayed pretty much anywhere.
It’s an interior insulator, and wires, small areas, and awkward corners don’t stop it. When you use spray foam, it expands on contact, filling every nook and cranny. That means you won’t have to worry about the roof’s R-value decreasing because of a missed spot.
Spray foam is one of the preferred insulation methods, especially for renovations. The main disadvantages are the aforementioned purchase cost, as well as the cost of installation because, unlike batts, you can’t DIY spray foam.
You should know that spray foam comes in two forms: closed-cell and open-cell. Open-cell spray foam is less expensive but provides a lower R-value. Consequently, it’s most appropriate in areas with very mild weather. Conversely, closed-cell insulation is more costly but provides better insulation.
Either form is inherently moisture resistant which means moisture can pass through it, but won’t damage the insulation. Before using spray foam though, always check with the manufacturer to ensure the foam and roofing materials are compatible. To learn more, see this MCA technical bulletin.
What’s the Best Metal Roof Insulation?
Now that you’ve read about the three most common options for metal roofs, you’re probably asking which one is best. The answer isn’t obvious. It depends on your project specifics and budget.
Looking to go for a low upfront cost? Choose fiberglass batts.
Installing a new metal roof, and want to make sure it’s very well insulated? Go for rigid boards.
Want great insulation for a renovation? Choose spray foam.
No matter which option you choose, remember to ensure that moisture won’t infiltrate your insulation and you will have a metal roof that will last a lifetime.
Thank you to the Team at Transcona Roofing for providing this content.
Since 1963, McElroy Metal has served the construction industry with quality products and excellent customer service. The family-owned components manufacturer is headquartered in Bossier City, La., and has 14 manufacturing facilities across the United States. Quality, service and performance have been the cornerstone of McElroy Metal’s business philosophy and have contributed to the success of the company through the years. As a preferred service provider, these values will continue to be at the forefront of McElroy Metal’s model along with a strong focus on the customer.