About Subfloors

There are many conditions which affect what type of flooring can be installed in a home. Two of the most crucial factors are subfloor and grade. Based on the subfloor and grade you can determine what installation methods you can use and what flooring options are available.

Grade

Grade refers to ground level. If your floor is going to be installed below grade, or below ground level, in a basement then you are limited to certain flooring options. Split-level homes where a portion of one level of the home is below grade and the remainder of the level is at grade are considered below grade for the purpose of installing floors. Floors which are below grade have a higher risk of moisture problems because of the concrete walls present as much of a moisture vapor issue as concrete subfloors.

Subfloors which are on-grade or above-grade have fewer limitations on what flooring can be installed, but it is still very dependent on the type of subfloor you will be installing your new floor over.

Subfloor

A subfloor literally is the floor beneath your floor. It is the structure upon which your new floor will be installed. Subfloors are typically the concrete foundation of your home or the wood laid over the flooring joists. The decision on which type of floor you can install and the method of installation to use depends on the subfloor you have. A floor is only as good as your subfloor – so before choosing which shade or species you want to install, take time to know what your subfloor is and what condition it is in.

Common subfloor types:

1. Concrete or cement.
2. Plywood – a panel made of three or more thin layers of wood bonded together using glue. The layers have alternating grain directions, usually oriented at right angles, to add strength.
3. Particleboard - made from wood particles (wood chips, sawmill shavings, saw dust) bonded together under pressure. Particleboard has a higher density than chipboard, and is a cheaper and less durable alternative to solid wood or plywood subfloors.
4. Orient Strand Boards (OSB) – made from long, narrow strands of wood or 1" – 2" wood chips and a resin binder. Like plywood, the layers are cross-bonded for strength.
5. Tongue & Groove – a panel with a general thickness of 3/4", similar to a standard plywood but with a tongue and groove. Tongue and Groove also includes an existing 3/4" solid hardwood that will not be removed.

Vinyl floors, glued-down carpets, and other existing flooring types are typically not suitable as subflooring (especially for wood floors) and must be removed. Before installing any type of flooring, it is important that you get down to the solid, flat and dry subfloor.

Here’s a quick reference on subfloors and the flooring types and installation methods you can use: