A Wood Floor That Can Survive Anywhere
In a basement or on a slab, create a stable platform to support quality engineered-wood flooring.
Synopsis: Creating extra living space in your house doesn’t necessarily mean building an addition. Many basements are viable options for conversion to livable space. To make a subterranean room feel even more homey, you can install a wood floor — which isn’t such a crazy idea if you use the method Charles Peterson outlines in this article. Peterson, a wood-flooring expert, recommends a system built in layers: first, the concrete slab; second, a layer of 15-mil polyethylene vapor retarder; third, two layers of 1/2-in. or 5/8-in. exposure-1 plywood; and finally, the finish flooring. This article includes a sidebar about choosing the best engineered flooring for a basement or slab project.
If you need more living space but don’t want to move, you’ve got a couple of options. Either you can build an addition, or you can put the space you already have to better use. The latter option often means finishing the basement. It’s a good option, too, because it can cost a fraction of what an addition might cost. Also, the basement is isolated from the main traffic paths of the house, so it’s an ideal setting for entertaining guests or relaxing with the family.
To me, nothing makes a basement feel more finished than a wood floor. It adds a sense of warmth and refinement that drastically changes the utilitarian feel of a space at or below grade. However, basements — and any concrete slab, for that matter — are notoriously moist, and moisture is responsible for more than 90% of all wood-floor failures. Installing a wood floor in a basement or on a slab so that it looks good and will last means controlling moisture, assembling an appropriate subfloor, and choosing the best engineered-wood flooring you can afford.
A floating subfloor is the best option
Wood flooring can be glued directly to a concrete slab or attached to a fabricated subfloor. Glue-down applications are intensive, and the best-performing adhesives are expensive. That’s why installing wood flooring over a subfloor is typically a better option.
There are many ways to build a subfloor. Plywood can be screwed to 2×4 sleepers that have been fastened to the slab on 16-in. centers. Plywood can be scored, glued, and nailed to the concrete, or it can be installed so that it floats over the slab without attachment.
The most cost-effective method, and the one that I and most professional flooring contractors prefer, is the floating subfloor approach. A floating subfloor is less labor intensive, doesn’t rely on expensive adhesives, and can be integrated with a vapor retarder more seamlessly than other subfloor assemblies.
Always install a class-I vapor retarder
Wood-floor manufacturers recommend that concrete slabs be tested for moisture content before their products are installed. If the moisture content of the slab is too high, the manufacturer specifies the use of a vapor retarder. This suggests that a vapor retarder doesn’t have to be used if the slab has a low moisture content at the time of testing. The problem is that testing represents just a snapshot of the concrete’s moisture level and does not factor in potential moisture levels. A class-I vapor retarder (commonly referred to as a vapor barrier) should always be installed despite a manufacturer’s recommendations about its use.
When you’re installing a wood floor over a concrete slab, the vapor retarder should be placed under the plywood subfloor. This installation contains the moisture in the slab, increases the subfloor’s stability, and helps to keep the finished floor from swelling, buckling, or cracking. Because a floating subfloor isn’t fastened to the slab, no fasteners are poking holes through the vapor retarder. The moisture in the air is another important consideration. Most wood-flooring manufacturers recommend that their products be installed in an environment that is a constant 60°F to 80°F with a relative-humidity level between 30% and 50%.
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