Most subfloors are built out of CDX tongue-and-groove plywood, although OSB (oriented strand board) has also been used in some cases. As a general rule, these subfloors are a minimum of 5/8-inch thick and range up to 3/4 inch in thickness. If a builder is worried about the bottom line, he tends to use the minimum thickness, but if the builder is worried about longevity and building a house to last, he’ll work with at least the 3/4-inch thickness. When building your own home, consider the fact that while you can save money on thinner material, it’s not as durable.
Above and Beyond
While carpet, hardwood and laminate materials are installed directly on top of a normal subfloor, ceramic tile and natural stone installations have extra requirements. For basic ceramic tile, you need to add at least a 1/4-inch-thick layer of backerboard on top of the subfloor, which adds to the overall height of the floor -- 1/2 inch is preferred. In the case of natural stone such as flagstone or granite and marble, the subfloor has to be even thicker, with two layers of 3/4-inch exterior-grade plywood required to build up the floor to withstand the weight of the stone.
Most concrete slabs are at least 4 to 6 inches thick and are poured on top of the ground so they don’t add to the overall height of the floor. However, in certain rooms of a house, such as entryways, tile or natural stone is desired; rather than use a backerboard, the builder often prefers to float a “mud" or concrete layer that is 2 to 4 inches thick to provide a base for the tile. Since this is too thick to match the rest of the finish floor, a special drop-down section of flooring is built into the frame of the home, with its own joist system that ties into the rest of the home. From here, two layers of 3/4-inch-thick plywood form the base for the concrete subfloor.
Traditional Flooring Material
Tile is generally 1/4 to 3/8 inch in thickness; natural stones are generally thicker, and you have to add at least 1/8 inch for the thickness of the concrete mortar beneath the tile after compression. Carpet ranges from 1/4 to 1/2 inch in general thickness. Laminate materials range from linoleum tile, which is around 1/8-inch thick, up to the look-alike wood planks that are 1/2 inch or so in thickness. Good hardwood will be around 3/4-inch thick, but varies depending on the type of wood you are working with.