Does open cell foam need a vapor barrier?

Asked By: Nayat Yturrat | Last Updated: 8th February, 2020
Category: home and garden indoor environmental quality
4.1/5 (35 Views . 44 Votes)
Open cell spray foam is not a moisture vapor barrier, and will allow moisture to pass. So, if you're considering spraying foam to the roof deck of your new or existing home, you want open cell. If there's a roof leak, water will pass through the foam, and you will quickly be able to find your problem.

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Herein, is open cell foam an air barrier?

Open-cell and closed-cell foams are air barriers. But open-cell foam will absorb and release moisture vapor more freely than closed-cell foam — which is a good thing. Open-cell foam is compatible with wood construction; both materials are air barriers that can absorb and release moisture.

Subsequently, question is, which is better closed or open cell foam insulation? Closed cell foam has a higher R-value than open cell foam, usually about 6.0 per inch. This higher rating makes closed cell foam better at keeping heat in or out of a structure. Open cell foams have an R-value of around 3.5 per inch.

Regarding this, do I need a vapor barrier if I use spray foam insulation?

Since spray foam is an air barrier and insulation, it stops the air flow and moisture movement. Open cell spray foam is required by code to have a vapor barrier installed. Most of the time it this will be in the form of 3-mil plastic sheeting.

What happens if open cell spray foam gets wet?

Open cell spray foam insulation will still dry completely after getting wet. In addition, because spray foam is not a “food” for mold, there is little danger of mold becoming a problem even if it gets wet. Closed cell foams also do not absorb water, which is very beneficial in flooding zones.

27 Related Question Answers Found

What is the difference between closed cell and open cell foam?

Closed cell foam has cells which are sealed off so air doesn't get inside the structure at all. The major difference between the two foam options is that closed cell foam tends to be harder or firmer while open cell foam is softer or less firm.

Is closed cell spray foam waterproof?

Is Spray Foam Insulation Waterproof? Open cell foam is not waterproof or water-resistant. In contrast, closed cell foam is water-resistant. However, only high-density closed cell foams are waterproof.

Does closed cell foam absorb water?

Open cell foam has a higher possibility of absorbing water than closed cell foam, which can lead to degraded performance, especially for thermal applications. If the environment is moist, closed cell foam might be the better option to work with as it's less likely to absorb water and become an ineffective insulator.

Is spray foam an air barrier?

The short answer is that closed-cell spray foam needs to be at least 1 or 1.5 inch thick to act as an air barrier, while open-cell spray foam needs to be between 3.0 and 5.5 inches thick to act as an air barrier.

How thick should open cell spray foam insulation be?


How Thick Does Spray Foam Insulation Need to Be? The thickness of spray foam really depends on where it's being applied and what you're trying to accomplish. Now generically speaking, we usually recommend open cell spray foam to be 6-inches on a roof deck or ceiling and 3-inches in the walls.

Does open cell foam mold?

According to Frank, moisture can be a concern if you construct a home and insulate it with open-cell spray foam. If closed cell is used, the moisture cannot make its way to the wood and present mold issues.

What is the R value of open cell spray foam?

Open-cell spray foam has an R-value of about R-3.7 per inch, while closed-cell spray foam has an R-value that may be as high as R-6.5 per inch.

Do you need ventilation with spray foam?

Most installations of spray foam insulation, when properly installed, act as an air barrier. When you use it instead of the fluffy stuff (fiberglass, cellulose, cotton), a house will be more airtight. That's good. Well, source reduction and separation would come first, but airtight homes need mechanical ventilation.

Do I need a vapor barrier?

In many colder North American climates, vapour barriers are a required part of building construction. You may find that vapour barriers are often not required in warmer climates. And, if installed in the wrong climate or on the wrong side of building materials, a vapour barrier can cause more harm than good.

Does Spray Foam cause mold?


Sealing the attic is probably the most critical, in terms of counteracting moisture. As a product, spray foam insulation does not attract mold. And unlike wood or metal, spray foam does not rot, rust or deteriorate. It will control indoor humidity and condensation, and therefore prevent mold from growing and spreading.

Is expanding foam water resistant?

Product Q&A
Moisture-curing, self-expanding foam adheres to all common building materials. Resistant to water, heat and ageing. Ideal for filling large holes, voids, gaps around window and door frames and around exterior pipes.

Does spray foam insulation cause moisture problems?

Spray Foam Myth: Insulating with spray foam insulation at the roof line will cause moisture problems with the roof sheathing. In an unvented attic scenario, to limit air leakage as well as any associated condensation at the roof line, a continuous air barrier is required.

Can you spray foam insulation yourself?

Quick & Easy Spray Foam Insulation:
An Air Barrier – Just 1 inch can seal the air leaks that cost you bundles. A Vapor Retarder – Our closed cell insulation does not absorb moisture, unlike open cell spray foam insulation, cellulose, or fiberglass. High-R Value Foam Insulation – R-7 in 1 inch of cured foam.

What is the R value of 2 inches of spray foam?

Open-cell spray foam absorbs and holds water. It has a lower R-value per inch than closed-cell foam and is vapor-permeable. The R-value is R-3.5 to R-3.6 per inch, so filling a 2×4 cavity yields about an R-13.

Is spray foam insulation worth it?


The EPA's Energy Star Association has shown that monthly energy bills can be cut by up to 20% when air leaks are sealed and efficient insulation is installed. The initial cost of spray foam insulation is well worth the investment, when factoring in the overall savings that will be headed your way over the long term.

How long does closed cell foam last?

With proper application, Spray Foam will last the lifetime of your home. Even roofing applications will last upwards of 30 years, with proper long-term maintenance. Spray Foam insulation adheres extremely well to virtually all substrates, and maintains its rigidity once dry.

Does closed cell foam absorb sound?

Closed cell foam is a specific type of foam that boasts a higher R-Value than its open cell counterpart. Because of this, closed cell foam results in a denser material that works better at absorbing low-frequency noise.