Does Spray Foam Insulation Cause Roof Damage? How Can It Be Prevented?

Posted on: 26 June 2018

You may have heard stories about how spray-foam roofing causes roof damage by causing the sheath of your roof to rot due to excess moisture buildup. While the risk tends to be greatly exaggerated, it can become an issue in some homes with open-cell spray foam insulation, especially in colder climates. Thankfully, damage can easily be prevented. Even though the risk is low, it may be worth taking the steps to arrest this problem before it occurs.

The problem arises because open-cell spray foam acts as a thermal insulator but still allows the movement of water vapor through the foam. Your roof by itself does not act as an insulator – during colder months, it will rapidly cool down to match the outside temperature. The open-cell spray foam insulation on the underside of your roof sheath will prevent these cool temperatures from radiating inside your home. The result is that the roof sheath is much colder than the spray-foam insulation. This temperature difference combined with the water vapor rising through the open-cell spray foam insulation causes condensation to form on your roof sheath, leading to rot and structural damage to your roof. However, this problem can be prevented by eliminating the source of the high humidity or by preventing water vapor from making its way through the insulation. Here's how.

Install a Vapor Barrier Underneath Your Open-Cell Spray Foam to Stop Water Vapor

In order to prevent condensation from forming on your roof sheath, you can prevent water vapor from rising through the open-cell spray foam insulation by installing a vapor barrier underneath it. Vapor barriers are particularly recommended in colder climates, where you are more susceptible to problems arising from condensation on the roof sheath. They are inexpensive and easy to install, making them a quick way to prevent condensation problems from occurring.

Vent Conditioned Air Into Your Attic to Reduce Humidity

One of the best ways to solve the problem is to simply connect your HVAC system to a small supply vent installed in the attic. By venting dehumidified air into your attic through a supply vent, you'll force out the humid air collecting in the attic. Keeping the relative humidity in your attic low will prevent condensation from forming on the roof sheath. An attic requires very little airflow in order to successfully keep humidity levels controlled, so a supply vent has very little impact on your energy bills. Controlling the humidity in your attic also makes it more comfortable when you need to go up into your attic, making this overall a better solution than just installing a vapor barrier.

Use Closed-Cell Spray Foam Insulation to Prevent the Issue Entirely

If you've heard stories about homeowners experiencing roof failure due to a rotting sheath after installing spray foam insulation and are wondering whether or not it's safe to install, know that you can avoid the problem entirely by installing closed-cell spray foam insulation. Closed-cell spray foam insulation is impermeable to water vapor, so there's no risk of condensation forming on the roof sheath. Closed-cell spray foam insulation is more expensive than open-cell spray foam insulation, but it forms a totally airtight seal around your attic.

Whether you decide to install a vapor barrier or condition your attic space with air from your HVAC system, you'll eliminate the risk of condensation forming on your roof sheath and causing damage. You'll be free to enjoy the increased energy efficiency of spray foam insulation without worrying about damage to your home. If you need assistance installing a vapor barrier or a supply vent, contact a company that specializes in insulation homes with spray foam roofing – they're experts in how to prevent excess humidity in your attic.   

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