Moisture Barriers for Flooring: The Ultimate Guide

Moisture barrier for hardwood floors

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.

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.

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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, Bostik GreenForce features a built-in moisture control membrane.
  • Water Resistant Materials: Materials like 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. 

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. 


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