Do I need a vapor barrier under my flooring?

Jul. 15, 2024

Moisture Barriers for Flooring: The Ultimate Guide

There are a variety of challenges to overcome when building or remodeling a home. Many of these are environmental and impossible to avoid. Moisture is a serious concern for contractors in cold and humid climates, and extra steps have to be taken to avoid negative effects on sensitive building materials &#; particularly hardwood flooring.

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Moisture barriers are commonly installed underneath flooring to prevent damage. However, not all cases require it. A contractor&#;s decision to install a moisture barrier is largely dependent on different variables like the flooring type, subfloor, and the local climate.

What is a Moisture Barrier?

A moisture barrier, also known as a vapor barrier or moisture retarder, is a moisture-resistant layer that&#;s placed beneath building materials to help prevent water intrusion. They&#;re most commonly used in the construction of walls and flooring.

Their primary function is to slow or stop the movement of water (as vapor, condensation, or liquid) through building structures so that degradation doesn&#;t occur.

Types of Moisture Barriers

There are multiple different types of moisture barriers for hardwood floors, with each being ideal for a different application:

Coatings:
A moisture barrier can be applied as a rolled-on, liquid coating which then forms a protective layer &#; one such product is Wakol PU 280
Built-in Protection: Additionally, certain products used in flooring installations may feature water reistant qualities. For example, in addition to being a powerful adhesive that you can use to install engineered flooring,
Additionally, certain products used in flooring installations may feature water reistant qualities. For example, in addition to being a powerful adhesive that you can use to install engineered flooring, Bostik GreenForce features a built-in moisture control membrane.

Water Resistant Materials: flooring underlayment are built specifically with water resistance in mind. These materials are built to function as a barrier to protect your hardwood floors from absorbing too much moisture from the subfloor.
Materials likeare built specifically with water resistance in mind. These materials are built to function as a barrier to protect your hardwood floors from absorbing too much moisture from the subfloor.

When Should a Moisture Barrier Be Used with Hardwood?

There are a few key instances when a moisture barrier should always be used. If a subfloor is made of concrete, an installer will always want to add one between the concrete and the flooring. This is because concrete&#;s porous nature allows moisture to seep through. If delicate flooring like hardwood is exposed to this moisture, warping, cupping, and other types of damage can occur.

It&#;s also advisable to use a moisture barrier when installing hardwood flooring in a subgrade area like a basement. This applies regardless of the type of subfloor.

Benefits of Using a Moisture Barrier Under Flooring

There aren&#;t generally downsides when it comes to installing a moisture barrier with hardwood flooring, so it&#;s worth it to put in the extra effort. However, the benefits are substantial. They include:

Mold-Resistance:
Mold thrives in dampness. If water or vapor can accumulate underneath a floor, growth is bound to develop.

Prevents Wood Rot:
Authentic hardwood and many other flooring composites are susceptible to rotting when exposed to water. A barrier avoids this situation entirely.

Prevents Cupping and Other Issues:
Since wood is hygroscopic, it responds to moisture in its environment by absorbing and releasing it. If exposed to too much moisture, your clients will experience cupping and other issues in their hardwood floors. Installing a moisture barrier under the floor can help prevent this.

Protecting a Flooring Installation

When gradually exposed to moisture, most flooring types will develop significant issues. A moisture barrier is an easy and affordable way to avoid these problems. It&#;s 100% necessary for projects involving concrete subfloors and damp spaces, especially when hardwood is being installed. Failing

to take this extra precaution will only result in a dissatisfied customer and disfigured, waterlogged flooring.

To ensure the satisfaction of your customers, choose the high-quality flooring products at City Floor Supply. Our in-house showroom allows you to demo your purchase before committing, and our affordable local delivery makes on-site installation a breeze.

Whether you&#;re working with a concrete subfloor or are building on top of a damp basement, we highly recommend that you include a durable moisture barrier in your flooring installation for long-lasting performance.

Frequently Asked Questions

Do I Need a Moisture Barrier Under Vinyl Plank Flooring?

A moisture barrier should be used when installing vinyl plank flooring on top of concrete. If it&#;s being installed on a plywood subfloor or existing flooring, this step can generally be skipped.

Do I Need a Moisture Barrier for Laminate Flooring?

Because of its multi-layer wood construction, laminate flooring should be installed with a moisture barrier. This is especially the case with concrete subfloors and when it&#;s being installed on top of damp spaces.

Do You Need a Moisture Barrier Under Hardwood Flooring?

Yes. Hardwood flooring is quite sensitive to moisture and it&#;s always worth adding a moisture barrier during installation. It is a necessity with concrete subfloors and damp areas, but water-resistive underlayments should be considered with other subfloors as well.

What is a Moisture Barrier and When is it Needed for ...

What is a Moisture Barrier and When is it Needed for Flooring?

Most people are unsure of what to do with a moisture barrier when dealing with flooring. Is it even needed? If so, when? More importantly, what does a moisture barrier do?

Overall, vapor barriers are misunderstood as a material that is only used for building walls. In reality, it&#;s used for both walls and floors, but for floors, they&#;re primarily referred to as moisture barriers.

By learning more about what moisture barriers do, and how to use them, we can answer the main overarching question: When you&#;re considering installing new flooring, will you need a vapor barrier? That&#;s what we are here to talk about and answer. Let&#;s dive in!

What is a Vapor Barrier?

Water vapor can cause serious damage to your home. For instance, if your flooring gets wet, it could cause mold and mildew, and even destroy your floor (source). No one wants that, so vapor barriers are there to help prevent the floor from getting wet.

Also known as a moisture barrier, a floor vapor barrier is typically a sheet of plastic that slows moisture from moving through a wall or subfloor. A moisture barrier is used when installing floors or walls in areas prone to dampness or excess moisture, such as basements, ceilings, or crawl spaces (source).

Flooring moisture barriers are placed beneath the floor&#;s underlayment. You can buy a barrier separately or get underlayment with a moisture barrier built-in. If any water vapor penetrates through a concrete subfloor, the vapor diffusion retarder slows the movement of the moisture, preventing damage to the floor.

SHOP MOISTURE BARRIERS SHOP UNDERLAYMENT WITH BUILT-IN MOISURE BARRIERS

Related Content >> Underlayment Buying Guide

Vapor Diffuser Classifications

Water vapor is measured in units called &#;perms&#; or permeability. To better understand a material&#;s ability to slow moisture&#;s movement, for instance, vapor barriers are categorized into three classes depending on how much water can permeate the material.

Class I vapor retarders:
This class of vapor barriers is impermeable. This means it does not allow fluid to pass through, making Class I the strongest vapor barrier class. Examples of Class I vapor barriers include, glass, sheet metal, plastic sheets, and rubber membranes.
Class II vapor retarders:
Class II refers to materials that are semi-permeable. This means some fluid can flow through. Examples include unfaced expanded or extruded polystyrene, 30-pound asphalt-coated paper, plywood, or bitumen coated kraft paper.
Class III vapor retarders:
This class of vapor barriers is permeable. Meaning water vapor can pass through. Examples of Class III vapor barriers include gypsum board, fiberglass insulation (unfaced), board lumber, concrete block, brick, or 15-pound asphalt coated paper.
(source
)

When Do You Need a Moisture Barrier?

To determine if you need a moisture barrier for your floor, you need to consider three factors: where you&#;re installing, the floor grade level, and the subfloor you&#;re installing over.

Climate

In mild climates, vapor barriers are not as common. However, if the climate around you is drastic, such as snowy winters, a lot of April showers, and humid summers, a vapor diffuser could be a necessity.

Grade Level

On some levels of the home, moisture barriers are more necessary than others. For instance, a basement is below-grade, so it&#;s more prone to moisture. Therefore, those levels that see more water vapor would need a moisture barrier. If the house does not have a basement, the ground level could be more susceptible to moisture.

Subfloor Material

You&#;ll typically need a vapor barrier if you&#;re installing flooring over concrete. Therefore, in high-humidity areas, moisture will move to a relatively low-humidity area, even through concrete. Therefore, because concrete is porous, it&#;s a good idea to install a vapor barrier over your concrete subfloor before installing your flooring. This way you can stop the vapor drive of water upward to your floors, protecting them from any damage (source).

Are you interested in learning more about Felt Flooring Exporter? Contact us today to secure an expert consultation!

Helpful Tip

To test to see if moisture is coming up through concrete, you can tape a sheet of plastic over the concrete and leave it there for 24 hours. If there is condensation on the plastic when you peel it up, you need a moisture barrier.

Once you have considered your climate and materials, you can decide if you need a vapor barrier for your floors.

How to Choose and Install a Flooring Moisture Barrier

Choosing a Flooring Vapor Barrier

There are different types of vapor barriers available for new flooring installations. Before installing your moisture barrier, it&#;s important to differentiate between each type, then choose which works best for your flooring. Let&#;s talk about the different barrier options for flooring installations.

Vapor barrier rolls that tape together, creating a full floating sheet. These rolls can also come with a self-taping option.
Underlayment that has a vapor barrier attached.
Moisture barriers that can be glued down to the subfloor.
Barriers that can be rolled, or painted on, which can also be used for showers.

Choosing a moisture barrier depends on the flooring that&#;s being installed. Therefore, when trying to find the right barrier, it&#;s important to talk to a sales representative or flooring professional, or review the manufacturer&#;s guidelines for the flooring. This ensures a suitable vapor barrier for your floor.

Installing a Flooring Moisture Barrier

Once you have the right moisture barrier, installation is easy. If the barrier is attached to your underlayment, simply install your underlayment, then put your new flooring on top.

If you choose a barrier that requires adhesive, such as tape or glue, all you need is the chosen vapor barrier adhesive, a utility knife or scissors, and your vapor barrier. The following are the steps for such an installation.

Lay out your moisture barrier in any area where moisture is a concern.
Go along one edge of the room and tape your sheet to the subfloor. When connecting two sheets, you should
overlap the sheets by six inches and use vapor barrier tape to bond the sheets together for excellent moisture control
.
Move along the room, starting from the same edge until the entire area is covered.

Remember, a vapor retarder should be a continuous sheet without any damages or holes. If there are punctures or tears, be sure to repair them before installation, as this could allow moisture to flow through (source).

Related Content >> Understanding Underlayment

Vapor Barrier FAQ

When should I use a moisture barrier on the floor?

Vapor barriers should be used on a floor when the area is prone to moisture. When moisture penetrates your flooring, it can cause mold, mildew, and the potential for water damage. A moisture barrier helps control the water vapor&#;s movement to help protect your floors. Therefore, if you&#;re installing floors in an area that sees moisture, even a little, a vapor barrier is needed.

Can you use plastic sheeting as a vapor barrier?

A moisture barrier is a material that reduces moisture from moving through other materials. Therefore, a plastic sheet can be a vapor barrier. In fact, plastic (or polyethylene) sheets are a Class I vapor barrier. Meaning, in terms of excellent moisture control, a plastic sheet is one of the best options.

How thick should a moisture barrier be?

Vapor barrier thicknesses range from 6 mils to 20 mils. 6 mil is the minimum for moisture control, with 20 mils being the most sturdy and puncture-resistant. The ideal thickness of a moisture barrier depends on how prone the area is to dampness. For dry areas, a 6-11 mil is standard. For wet or humid climates and areas, you should be using a 12 mil or higher.

What is the best moisture barrier for laminate flooring?

For any flooring that requires a floating installation method, be laminate or vinyl planks, use a 6 mils (or thicker) plastic sheet as a moisture barrier. You can also use an underlayment with a moisture barrier built-in for water vapor control.

How long does a flooring vapor barrier last?

A vapor barrier underneath flooring will last as long as the floor. After the floor has been installed, the vapor barrier underneath will not get damaged over time since it&#;s not stepped on or exposed to other elements.

Do you need to tape vapor barrier seams?

You need to seal the seams between moisture barriers to prevent water from getting through. To do this, you can use vapor barrier seaming tape. To ensure excellent moisture control, layer the sheets over each other by six inches.

Conclusion

Now that we broke down the ins and outs of vapor barriers, you&#;re ready to install new flooring in your basement, bathroom, or wherever! You know what to do to make sure you have the moisture in your home under control.

If you&#;re looking for flooring inspiration, we have the perfect place to start your search.

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