What are the problems with foam board insulation?

Author: Prof. Maxine Heaney  |  Last update: Monday, May 5, 2025

Expanded polystyrene foam boards are made with air bubbles that stop heat transfer. Unfortunately, those same air bubbles collect moisture which leads to mold and mildew growth. Solution: Rigid foam board insulation products are actually made to be water resistant. Air leakage.

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.

What is the downside of foam insulation?

Spray foam insulation is a good insulator in terms of keeping a room warm or cool. But its many downsides outweigh the benefits. These include, making it more difficult getting a mortgage, potential health issues, environmental damage, ventilation issues and a lower home valuation.

Will mold grow on foam board?

Although its surface properties are not very conducive to the direct and rapid attachment of mold, if the environmental conditions continue to be unfavorable, mold may still find a foothold on polystyrene foam and gradually grow and spread.

Do you need an air gap with foam board insulation?

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.

Spray Foam Insulation — The Ugly Truth?

Do you need a vapor barrier over foam board?

In general, if the foam rigid insulation is installed correctly and sealed properly, a vapour barrier may not be necessary. However, there are certain situations where a vapour barrier is recommended, such as in areas with high humidity levels or where there is a risk of moisture infiltration.

Should you leave a small gap between the insulation and the boards?

It is important to leave a small air gap between boards and the mineral wool in order to stop damp forming. Remember that insulating between the joists will create a cold roof space as the heat is kept underneath the insulation like a blanket.

Does foam board insulation need to be covered?

That said, it's still advisable to cover any foam board insulation exposed to the Sun within 30-60 days at the most.

What insulation doesn't mold?

Generally speaking, closed-cell insulation (i.e. cellular glass, phenolic, polyiso, and flexible elastomeric foam) is more resistant to mold spores than open-cell insulation (i.e. fiberglass).

What is the best rigid foam insulation for exterior walls?

The best kind of rigid foam insulation is polyisocyanurate, also known as polyiso. It has the highest R-rating of any rigid foam insulation and comes with a reflective foil on both sides, allowing it to act as a radiant barrier as well.

What is the best insulation for a house?

The best performance available is spray foam insulation. An attic with spray foam will perform better than blown-in can, even with an air-seal. If you choose blown-in insulation for your attic, we recommend air-sealing the attic floor first. An airtight seal maximizes the performance of insulation.

What is the life expectancy of foam insulation?

Closed-cell spray foam is exceptionally durable, lasting up to 80 years or more. Open-cell spray foam has a shorter lifespan of about 20 years. Both types excel in gap-filling, providing excellent insulation by expanding to fill cracks and crevices.

What are the disadvantages of foam?

One of the main drawbacks of polyurethane foam is the potential for chemical emissions. Volatile organic compounds (VOCs) released during manufacturing and off-gassing can affect indoor air quality. Polyurethane foam is highly flammable.

Why is foam insulation a problem?

Potential problems with spray foam insulation

If incorrectly installed or used inappropriately, spray foam insulation might: reduce air circulation and ventilation within a roof space. lead to dampness and condensation on the underside of a roof because it forms an air barrier and stops moisture from escaping.

What is an alternative to foam board?

Yes – there are many other graphic substrates including polystyrene, sign blank, coroplast, fabric, and plexiglass (to name a few) but these three are the most common and widely used rigid materials.

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.

Does foam insulation grow mold?

Mold and mildew can begin growing behind the insulation which can go unnoticed until it's already become a huge problem. This often happens when the spray foam isn't installed correctly and space is left between the insulation and the wall, which allows moisture in and gives mold the perfect place to grow, unfettered.

What happens to insulation when it gets wet?

Every type of insulation will react differently when it gets wet. Fiberglass insulation will lose its effectiveness as air is displaced by water, causing it to conduct heat instead of insulating your home. Cellulose will begin degrade if it's not dried quickly, and it can start to grow mold.

How to dry out an attic in winter?

In winter, temporarily open windows just a little to allow warm moist air to leave the home and also allow cold, dry air to come in. For a short-term fix you can put a dehumidifier in your attic, but understand that you may be emptying it multiple times a day.

What are the cons 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.

When should I stop wearing foam boards?

FOAM/BOARDS: Add foam inside your compression garment within 24 hours of surgery (see video above) for any liposuction areas to create even compression. Recommend wearing a polyester layer directly over the skin first to prevent skin irritation. Foam is continued for 1 month post op minimum.

What happens to foam board if it gets wet?

Yes, it can get wet without absorbing water. However, water pressure can damage the foam, potentially compromising its insulating properties.

Do you need to tape seams of foam board insulation?

Sealing those seams also keeps moisture from getting into the building or home. Without those sealed seams, there can be a lot of issues such as damaged walls and mold to contend with. That is why choosing the right seaming tape is so important.

Is it better to insulate the ceiling or the roof?

The answer to these issues may be adding insulation, but that still leaves the question of where to apply additional thermal protection to see the most benefit. While both ceiling and roof insulation will increase your home's resistance to outside temperatures, insulating the ceiling should be your priority.

Do you need a vapor barrier on both sides of insulation?

Joe Lstiburek, an engineer and principal with Building Science Corp. in Westford, Mass., responds: Installing a vapor barrier on both sides of a wall is never a good idea in any climate.

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