Best Vapor Barrier Products For Roofs

Congratulations on your new roof! Replacing or repairing a roof is rarely how we want to spend our time and money. However, roofs are a vital part of home construction. Whether you’re building a brand new home or helping your current house last longer, you need to know what products are best for your roof. Do roofs need vapor barriers? If so, what product should you use?

South Central Services has insulated hundreds of new and existing homes with spray foam. Attics play a crucial role in home energy efficiency, so we have a lot of experience insulating the undersides of roofs.

By the end of this article, you will know:

• What vapor barrier products can be applied while inside your attic
• What vapor barrier products are applied from the roof of your home

Interior Vapor Barrier Products

Sometimes, you can get a new roof feel without replacing the entire roof. In these situations, your shingles still have life in them, but your home is experiencing some vapor transfer difficulties. While vapor barrier products do not handle roof leak issues, these products can keep excess humidity out of your attic and living space.

Let’s look at the two most common products used to create vapor barriers from within your attic.

1. Fluid-Applied Vapor Barriers

Fluid-applied vapor barriers usually come in large buckets with resealable lids. Fluid-applied vapor barriers are most commonly used on walls, but can be used for roofing applications.

In a roof application, this product would be applied in an even layer to the interior side of the roof. Each manufacturer would provide specific instructions on how to install their vapor barrier product.

While handy homeowners can install fluid-applied vapor barriers, we recommend working with a professional contractor to ensure an even application. Professionals can also identify how that product needs to work with your existing attic situation. Do you have HVAC ductwork, insulation, or baffles that would interfere with the vapor barrier application?

2. Closed Cell Spray Foam

Another product used to create a vapor barrier is closed cell spray foam. One of the benefits of closed cell foam is its multifunctionality. While fluid-applied vapor barriers are only used as a vapor barrier, closed cell is primarily used as insulation.

If your roof needs a vapor barrier and your attic needs new insulation, closed cell spray foam will allow you to kill two birds with one stone. By encapsulating your attic with closed cell, you can create a conditioned space upstairs while also stopping vapor transfer.

Unlike fluid-applied vapor barriers, closed cell spray foam must be installed by a professional contractor in this application. Not only are DIY spray foam kits difficult to monitor and control, but spraying overhead adds an additional layer of complexity for a homeowner. Find and hire a qualified contractor to handle your attic encapsulation.

Exterior Vapor Barrier Products

Sometimes, a new roof means just that: a new roof. If you’re in the process of replacing your roof, there are a few products that are commonly used to provide a vapor barrier before placing shingles. Let’s examine these products in more detail.

1. Peel-And-Stick Membranes

Peel-and-stick membranes can create vapor barriers. Not every peel-and-stick membrane is vapor impermeable. However, the right product installed correctly can deliver a vapor barrier.

One of the benefits of peel-and-stick membranes is their adhesion. Without additional fasteners, these membranes can stay in place on your roof.

Peel-and-stick membranes can be made of different materials, such as aluminum, laminate, or plastic.

If you plan on replacing your roof altogether, we recommend working alongside a professional roofer at a minimum. You can also discuss the use of peel-and-stick membranes with this professional, given your climate zone and their experience.

2. Roofing Underlayments

Another potential vapor barrier that can be used when replacing a roof is roofing underlayments. Not all roofing underlayments can create a vapor barrier.

Roofing underlayments may look just like peel-and-stick membranes when you research online. However, one of the key differences between them is their adhesion. Peel-and-stick membranes adhere to surfaces, while only some roofing underlayments adhere.

Roofing underlayments may be made of polypropylene, felt, rubberized asphalt, or other materials.

Like peel-and-stick membranes, it is best to consult a professional about which product is best for your roof. Which vapor barrier product to choose can be influenced by the design and materials of your roof.

Which Vapor Barrier Product Is Best For My Roof?

This article is not an exhaustive list of vapor barrier products for roofs. After all, we are not roofing contractors! However, this list is an excellent starting point for a conversation with a qualified roofing contractor.

What type of vapor barrier is best for your roof will depend on a variety of factors, including:

• Climate zone
• Roof design
• Stage of roof construction
• Existing leaks or other roof issues

Most likely, your roof will need a vapor barrier, and one of these products will be the best choice to help keep humid air out of your home. Consult a professional roofing company to determine what your roof needs.

The Bottom Line About Vapor Barrier Products For Roofs

Roofs have numerous options for vapor barriers, including fluid-applied products, closed cell spray foam, peel-and-stick membranes, and roofing underlayments. Which product is best depends on where you are in the construction process and other factors.

When replacing or repairing a roof, it is important to work with a professional contractor.

Now that you understand what products are commonly used for roofing vapor barriers, your next step is to:

• Learn more about attic encapsulation
• Compare attic insulation options
• Discover how heat travels in a house