Subflooring Weight Vs. Strength

Weight

• Wood subfloor materials, such as plywood and OSB, come in panels. The weight of panels is influenced by the thickness, density and wood species used to construct them. As a result, panels vary in weight by as much as 20 percent. The standard weight measurement is described in pounds-per-foot. If the subfloor panel is too light, it will create deflection, which is the term builders and engineers use to describe the bending or deformation of the flooring structure from heavy objects and heavy foot traffic and activity. For example, a subfloor in a living room needs to be heavy to support furniture and people.

Strength

• The subfloor must be strong enough to support the weight of the tiles, laminate or wood flooring that will be laid on top, so that it does not bend, warp or buckle. Builders and engineers assess the bearing strength, bending strength and bending stiffness of subfloor materials when they make their selections.
  The bearing strength is the ability of the face panel, which is the side of the panel that’s on top, to resist crushing from weight, such as a heavy piece of furniture. The bending strength is the ability of the material to accept weight without breaking. Bending stiffness is also a consideration. Panels with high stiffness reduce the occurrence of a floor that feels bouncy. A stiffer subfloor also reduces the occurrence of tiles popping out of place and cracking.

Making Weight and Strength Improvements

• You can perform a simple test to detect deflection and weak spots. Walk over the bare subfloor to see if there are areas that flex. Improve the strength of the subfloor by adding a new layer of plywood or Oriented Strand Board, called OSB, on top of the existing subflooring material that hasn’t deteriorated. In some cases, a 3/8-inch or 1/2-inch layer of new plywood or OSB, placed at a 90-degree angle over the existing subfloor will suffice to strengthen and stabilize the floor joists and improve the overall strength and structural integrity of your subfloor.

Comparing Weight and Strength

• Just because one subfloor material weighs more than another does not always make it the right choice. The subfloor material must match the architecture and structure of the home on each floor. For example, wood planks might work on a first floor of a home, but the home’s framing and floor joists might not support them on a second floor. Follow manufacturer’s recommendations for the type of flooring you will use. And check with your local building code agency and professional builders to select the appropriate subfloor materials for your home to comply with code and safety standards in your area.