Basement Subfloor Options

Basement Being Finished With Sub-Flooring

Perry Mastrovito Design Pics / Getty Images

Basement subflooring has so many jobs at hand. Unlike above-grade sub-flooring, basement sub-floor has to do all of the usual things—and plenty more.

Not only should subflooring provide a flat, level surface for the finish flooring, but it must also keep moisture in check and insert a thermal break to control temperates in the basement. If the basement does happen to flood, the subfloor should be able to dry out easily and quickly.

Is the solution to the moisture problem to add a high subfloor? Not usually, since basement ceilings tend to be low. This means shaving down the height of the subfloor to increase the floor-to-ceiling span.

That's the challenge of building a basement subfloor. Fortunately, there are do-it-yourself and pre-made solutions that can help.

What a Basement Subfloor Is

A basement subfloor is a layer that is built below the floor covering (carpeting, laminate, etc.) and above the bottom-most floor, usually concrete.

Subfloors are not always necessary but they are beneficial wherever they can be installed. They only come into play when you want to expand downward and make your basement a warm, livable space. If you don't plan to use the space, there is no need for a subfloor or floor covering. Concrete or tile-over-concrete are acceptable floors for uninhabited basements.

But to install any kind of floor covering—engineered wood, laminate, carpeting—basement subflooring is highly required.

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Subfloor Factors: Moisture and Height

Moisture Entering the Basement

Even if you do not expect catastrophic events such as flooding, moisture can invade your basement in other ways.

Since basements are essentially holes in the ground lined with concrete, and moisture is pervasive in the ground, water vapor can gradually work its way upward through concrete basement flooring and condense.

So, basement subflooring should provide a reasonably high buffer from moisture that may transfer from below.

Height of Basement Ceiling

An unusually high basement subfloor in the range of 8 to 10 inches would allow your basement to stay dry above most moisture that comes its way. But this is not practical.

Basement ceilings tend to be low. Full 8-foot tall basement ceilings in older homes are rare, with 7-footers more the norm.

So, the basement subfloor and the basement ceiling relate to each other. Raising the subfloor has the effect of lowering the ceiling. Even an inch or two in elevation for your subfloor will make a noticeable difference.

Two-by-Fours and Plywood Subfloor

Building a basement subfloor from two-by-fours topped with plywood is a traditional method. One plus is that costs are kept low. On the downside, height is a problem, as it employs a system of two-by-four sleepers.

From top to bottom, this list of materials is shown in the same order that you would visually see these materials in a cross-section:

  • Floor covering
  • Plywood fastened to the sleepers
  • Two-by-four sleepers installed on center every 12 to 16 inches and fastened down, with rigid foam insulation 1-1/2-inch thick placed between the sleepers
  • Vapor retarder
  • Concrete basement floor

Note

The vapor retarder is 10 or 15 mil sheeting of the type found at home centers or hardware stores. Plywood is 1/2-inch exterior grade kiln-dried plywood.

Floating Plywood Subfloor

As the least-expensive subflooring option, floating plywood's only barrier between the concrete and the plywood is plastic sheeting. The advantage of this type of basement subfloor is that it is thin and easy to install.

Rigid Foam Insulation Subfloor

Rigid foam is an excellent basement subfloor option because it provides a thermal break between concrete and flooring.

  • Finish flooring
  • Plywood screwed down through the layer below
  • Rigid foam insulation—1 1/2-inch thick
  • Concrete basement floor

Specialty Premade Subfloor Systems

Subfloor systems eliminate the multi-layer approach of the do-it-yourself systems, giving you all of the layers fused into tiles or panels. These tiles are easily attached to each other and the subfloor goes down fast. The downside: the significantly higher price.

Barricade is one such brand of premade subfloor system: 2-foot by 2-foot by 1-1/8-inch tiles with OSB wood on top and closed-cell polystyrene insulation on the bottom. The chief advantage of subfloor systems is the thinness of the product.

  • Finish flooring
  • Subfloor module (Brands such as Barricade, Subflor, etc.)
  • Concrete basement floor

Tyroc is another such brand of premade subfloor panels. Coverage per panel is 5.3 square feet, with each panel measuring out at 48 inches by 16 inches. Tyroc claims that it has the thinnest profile of any other product in its category.