Moisture Barriers: What They Are and Why You Need Them

If you're planning on having new hardwood flooring installed and you've done your homework, you probably know that most installation jobs require some sort of moisture barrier between the new boards and the existing subfloor. But what are moisture barriers, exactly? And why are they so important? Good questions. Check out the info below to find out all you need to know about moisture barriers!

What are moisture barriers?
Moisture barriers, also called vapor barriers or vapor retarders, are layers of material that help prevent moisture-related problems in your floors by protecting the wood from ground moisture and condensation. They also help reduce the amount of noise floors make and prevent damaging wood-on-wood contact.

Why do I need moisture barriers?
Ground moisture and condensation are a few of the biggest threats to hardwood floors. Dramatic changes in humidity and ground moisture can cause wood boards to shrink and expand more than they should, which can lead to gapping, warping, and buckling. Moisture barriers help prevent the wood from absorbing excess moisture, preserving their stability and helping reduce the amounts of moisture-related problems.

What kind of moisture barriers are out there?
There are three main types of moisture barriers: impermeable, semi-permeable, and permeable. These different levels of permeability allow you to install wood floors over different types of subfloors. Wood subfloors, for instance, do better with an impermeable barrier with a permeability rating greater than 0.7; anything less can cause moisture to be trapped below or on the subfloor. Concrete subfloors, on the other hand, require a very high level of impermeability; usually .15 perms or lower. This allows for little to no moisture movement.

Does the installation method change the type of moisture barrier I'll need?
Yes, insomuch as different installation methods are required for different types of subfloors. Moisture barriers offer protection in one of three ways:
The first kind of protection is for nail down install jobs. This involves placing a layer of 6 mil poly sheeting plastic over the dirt in the crawl spaces beneath the subfloor, then placing a 15-pound felt paper between the subfloor and the hardwood.
The second kind of protection is for glue down installations and usually requires using a trowel-applied moisture barrier (such as Bostik) since plastic barriers can prevent the glue on the floors from sticking to the subfloor.
The third kind of protection is for floating floor installations and also involves a 6 mil poly sheeting plastic barrier under the boards. Unlike nail down installations, however, plastic barriers shouldn't be used if the floating floors are covering wood subfloors as they prevent the subfloor from breathing.

What if the floor is above grade? Do I still need a moisture barrier?
Yes. For above grade floors, a 15-pound felt paper works wonders. This moisture barrier should be laid between the hardwood and the wood subfloor; this is the best way to reduce the amount of moisture that can get to the new flooring.

Confused? Don't worry. It's not your job to understand all the technicalities of moisture barriers and hardwood flooring installation. However, knowing the basics about this important flooring component can help you better understand the installation process in general and allow you to make sure your flooring installer is doing the job right. Visit Fantastic-Floor.com to learn more about moisture barriers and solid hardwood flooring installation, or give us a call at 1-888-448-9663.