Plastic Flooring Installed on Top of Wood?

Photos courtesy of NWFA unless otherwise noted

A scenario no wood flooring professional enjoys is if a customer asks to install LVT, SPC, or other plastic surfaces on top of their real wood floor. However, this seems to be a common occurrence. So why has this become problematic for the wood flooring industry?

Installing a class I vapor retarder over a wood floor is never a good idea.

A class I vapor retarder, also called “vapor-impermeable membranes” or “vapor barriers,” normally are installed to stop moisture from entering the building. Common uses include:

  • Below concrete slabs that are intended to be used for a residential or commercial interior substrate.
  • Over the ground surface in crawlspaces.
  • On the underside of the joists to stop moisture from entering the subfloor assembly.

It is never a good idea to use these vapor-impermeable membranes directly over wood subfloors. Doing so will effectively block moisture from getting to the wood floor, but also could lead to trapped moisture within the subfloor assembly, resulting in subfloor decay, rot, mold, or mildew growth.

Photo courtesy of Footprints Floors

Wood is a natural material. One limitation that can shorten the service life of wood is its vulnerability to moisture and decay. When moisture is trapped, and the wood is suffocated by an impermeable membrane, such as a plastic barrier, the same biological process that decomposes dead trees in the forest will happen to the floor.

Within the home, nature will do what it always does; it will attempt to equalize. Water vapor generally migrates from areas of higher temperature and relative humidity to areas of lower temperature and relative humidity. This is called vapor drive. Vapor drive typically moves moisture from these unconditioned spaces to the indoor space in and through the floor assembly.

Wood floors installed above unconditioned spaces are susceptible to moisture. The wood floor is reactive to the moisture. It is hygroscopic, meaning it swells with a gain in moisture, and shrinks with a loss of moisture. The reality is that wood floors are a great barometer of conditions within the home.

When moisture gets trapped in the wood floor by laying a vapor-impermeable floor covering on top of it, the moisture gets trapped, which can lead to decay, rot, mold, and mildew. | Photo courtesy of Dan Natkin, Bauwerk North America

Vinyl, plastic composite, and laminate flooring is generally impermeable. So what happens when impermeable floor coverings are installed over a wood floor? When this moisture gets trapped in the wood floor by laying a vapor-impermeable floor covering on top of it, the moisture gets trapped, which can lead to decay, rot, mold, and mildew.

According to Joe Lstiburek, founding principal of Building Science Corp, the incorrect use of vapor barriers is leading to an increase in moisture-related problems. Vapor barriers originally were intended to prevent assemblies from getting wet. However, they often prevent assemblies from drying. Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. When the vapor barrier is the floor covering, you have problems.

If you think logically about it, anything promoted as being “waterproof” insinuates that the product will not allow moisture to pass through it. This is consistent from both sides of the product: from above and from below. As the newest floor covering category in the market, it also has had its trials and tribulations during the last several years. One of those is related directly to its permeability. Trapped moisture in a wood floor or subfloor assembly is not good.

When moisture gets trapped in the wood floor by laying a vapor-impermeable floor covering on top of it, the moisture gets trapped, which can lead to decay, rot, mold, and mildew. | Photo courtesy of Dan Natkin, Bauwerk North America

According to the National Association of Home Builders (NAHB), International Code Council (ICC), and the ICC Evaluation Service (ES), in cooperation with Innovation Research Labs, the chart above provides the typical ranges of vapor permeance for common interior floor coverings.

The floor covering industry has watched the vinyl and plastic composite flooring category outperform other flooring categories, in percentage of growth, during the past several years. Although this trend seems to be plateauing, it still accounts for a large segment of the industry.

Photo courtesy of commons.wikimedia.org

Wood can last for centuries when it is taken care of. For example, the Braman-Nothnagle Log House in New Jersey was constructed in 1638. This historic home contains North America’s oldest known surviving wood floors, making them 385 years old. Wood floors much older than these exist in even older, more historical parts of our world.

 

Consider why these plastic floors are being promoted and why they are so easy to sell.

  • Price-point. It’s cheap. It took our industry by storm as an affordable, entry-level floor covering option. It has uprooted the entry-level wood flooring market (which is not a bad thing).
  • Improved Visuals. These products look more and more like real wood. At a glance, even professionals can have difficulty differentiating some of these products from the real thing.
  • Easy Installation. It can be installed by anybody, with very little skillset.
  • “Waterproof” Promise. I know this is a controversial topic, but that is not what this article is about. Waterproof is defined by Merriam-Webster Dictionary as something impervious to water. This includes not only liquid water, but also water in vapor form.

For the uninformed sales professional, who is often the final influencer of the buyer’s flooring purchase, these are easy selling features. Unfortunately, when sold and installed in the wrong situation, some of these features can contribute to health and structural-related failures.

The most-common failures occur when these plastic floors have been installed on top of wood floors and subfloors that are over either unconditioned spaces (crawlspaces, unfinished basements, garages, etc.) or over a concrete slab.

There is a place for these types of floors to exist, just not over the top of a wood floor or over unconditioned space. Alternatively, when a customer does ask for plastic to be installed over their wood floor, focus on these positive attributes of wood:

  • Most wood can be refinished.
  • Demonstrate wood flooring’s durability.
  • Emphasize the natural beauty of real wood flooring.
  • Educate customers about the easy care of wood flooring.
  • Tell wood flooring’s “green” story.
  • Tout the health benefits of living with wood flooring.
  • Explain the long-term value of wood flooring.

Wood can last for centuries when it is taken care of. For example, the Braman-Nothnagle Log House in New Jersey was constructed in 1638. This historic home contains North America’s oldest known surviving wood floors, making them 385 years old. Wood floors much older than these exist in even older, more historical parts of our world.

Durability, attractiveness, and ease of maintenance are some of the most important attributes of a homeowner’s flooring selection. When homeowners are asked what flooring they would have in their “dream home,” two-thirds said they preferred wood floors. If customers want wood, why sell them a plastic imitation?

Brett Miller is the vice president of technical standards, training, and certification for the National Wood Flooring Association in St. Louis. He can be reached at brett.miller@nwfa.org.

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