Does foam board work as insulation?

Author: Prof. Lavada Luettgen DVM  |  Last update: Friday, June 13, 2025

Foam board can be used to insulate any exposed cavity in your home from the top to the bottom, and even the walls if you are remodeling and the drywall is down. It can also be installed in the open cavities of your pole barn.

Can I use foam board instead of insulation?

Yes - interior foam board is a well-tested method for improving thermal performance and comfort in a renovation.

Is foam board a good insulator?

Foam board insulation provides excellent thermal resistance and is moisture-resistant, making it great for preventing heat loss and damp issues.

What are the disadvantages of foam board insulation?

Insulation Foam Boards Don't Work On Uneven Walls

This allows moisture to seep in. Excess moisture can cause mold, mildew, odors, decay, fungus growth and wood rot.

Can foam poster board be used as insulation?

Foam board is commonly used for photo mounting, signage, presentations, architectural models, and insulation.

Which Foam Board? Polyiso vs XPS Insulation

Does foam board insulation need an air gap?

Insulation boards are no exception to this rule, and it's important to leave an air gap between them and the surface they're installed on.

What is the R factor of foam board insulation?

The R-value of rigid foam insulation varies based on the materials used and how many layers are installed. For example, our polyiso rigid foam boards have R-values between 6.5 and 6.8 per inch. If two layers are installed, it doubles the R-value and cuts heat/conditioned air loss in half.

Do I need a vapor barrier if I use foam board?

Therefore, it is generally recommended to use a separate vapour barrier in conjunction with PIR foam board insulation in order to provide adequate moisture protection.

What is the life expectancy of foam board insulation?

Foam board insulation, including types such as polystyrene, polyisocyanurate, and polyurethane, has a lifespan of 30 to 50 years. This type of insulation stands out for its moisture resistance and high thermal resistance, which contribute to its longevity and effectiveness in various applications.

Can mold grow on foam board insulation?

Under certain environmental conditions, such as high humidity and the presence of organic pollutants, the surface of polystyrene foam may gradually accumulate moisture and nutrients, thereby providing certain conditions for the attachment of mold.

Do I need house wrap if I use foam board?

House wrap helps prevent moisture damage, but when coupled with foam siding they create an unstoppable force. Moisture Management System for your home: It's estimated that each person uses 80-100 gallons of water per day at home. Instead of that moisture becoming trapped inside the home, foam can help it escape.

How thick should foam board insulation be?

How Thick Is Rigid Foam Insulation Board? Rigid board insulation generally comes in standard thicknesses ranging from ½ inch to 2 inches. It is possible for homes located in extreme climates to order specialty thicknesses of up to 6 inches directly from certain manufacturers.

Why is foam board insulation so expensive?

Insulation costs vary depending on the materials used. For instance, foam board insulation tends to be pricier than fiberglass or cellulose because it offers a higher R-value and better moisture resistance, impacting both the product cost and the effectiveness in controlling temperature.

Can I insulate my attic with foam board?

Side attics insulated with rigid foam board will maintain a more consistent temperature throughout the year. That makes them better for storing personal items as well as HVAC equipment. For example, it's not uncommon to see an air handler for a heat pump in a side attic.

Should you tape foam board insulation?

That's what makes sealing the joints between rigid insulation boards so critical. This step keeps air and other elements from seeping through the cracks and into your building's interior by performing as an air and vapor barrier. There are many construction tapes on the market to pick from.

Does foam board insulation keep heat out?

The graphite in these foam boards reflects radiant heat, complementing the foam air bubbles' ability to block conductive heat. This unique function gives them a relatively high initial R-value of 4.7 per inch.

What are the negatives of foam board?

Cons of a Foamboard

Foamboards can get discolored, disintegrated or warped if left under the sun or rain. It can be used for a short outdoor event and not as a permanent outdoor display. Also keep it away from your bathroom or kitchen as steam can create moisture, affecting the foamboard.

Does foam board lose R-value over time?

Over the course of time, the R-value drops because the added blowing agents found in the final product eventually is replaced with air making the product less heat resistant. An initially rated R-value 5.0 XPS product will eventually drop to closer to an R-value of 4.3.

Can foam board insulation get rained on?

Insulation boards tend to have good moisture resistant and water repellent qualities. Products such as Celotex and EcoTherm boards for instance have aluminium foil facings on both sides, and a PIR foam that is resistant to water.

Can foam board be used as insulation?

Rigid Foam as an Insulation Strategy

The boards are available in several thicknesses and R-values; 1-inch and 2-inch thicknesses are common. Rigid insulation provides thermal protection and it can also serve as an air and moisture barrier.

When should you not use a vapor barrier?

Because a vapor barrier is a low permeable barrier, it keeps moisture from passing through. This is beneficial to keep moisture away from a dry surface but will trap moisture behind it if installed on a water-damaged concrete wall, causing the wall to fail further.

Is pink foam board a vapor barrier?

The pink extruded foam must be at least 2" to be considered a vapour barrier/retarder. Anything less is not considered so.

What is the thinnest insulation with the best R-value?

The thinnest insulation material currently available on the market is the 10mm Aerogel blanket. Its manufacturing technology is highly interesting, and its appearance resembles frozen smoke. For some, aerogel is synonymous with time frozen and suspended in space.

Is there a big difference between R13 and R15?

R15 insulation offers slightly better thermal insulative properties than R13. Some of its formats are a fraction of an inch thicker than R13, making it more effective at helping with energy efficiency. However, the difference is minimal.

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