Fastening Subfloors

Application Info: Fastening Subfloors

Tired of Squeaky Floors? Floors are a system consisting of the joists, subfloor, and finished floor. Improper installation of the subfloor practically guarantees squeaks, but unfortunately, proper installation doesn’t absolutely prevent them.

Solving the squeak problem requires a basic understanding of its cause. Squeaks occur when one material moves against another. Most often, squeaks result when a nail fastening the subfloor (or finished flooring if it is nailed down as well) begins to back out or loosen as the floor joist and subfloor dry out. As the subfloor dries, it shrinks in thickness. This leaves a small portion of the nail head above the surface. Over time, foot traffic near the nail will cause the nail to gradually loosen in the hole, allowing the subfloor to rub against it, which creates a squeak.

The squeak solution is to eliminate any possible movement between the three components of the floor system. In the case of the subfloor to joist connection, this is easily accomplished by gluing down the subfloor with construction adhesive (it comes in a tube like caulk). The glue prevents movement, and acts as a gasket to minimize variations in the joist surface. Screws are used to clamp the subfloor in position and assure a solid connection to the joists. Of course, screws will not back out of the hole like nails, and the threaded shank prevents the rubbing that causes squeaks.

Screw Selection: For applications using 3/4” (23/32”) plywood or Oriented Strand Board (OSB), 2” long screws are sufficient because of the number of fasteners holding the subfloor in position. In most applications, #8 screws are sufficient. Screws should be driven at every joist on 12” centers, and on 6” centers along the edges parallel to the joists. If you are counting, that results in the use of 43 screws per 4 x 8 ft sheet when installed with the long edge perpendicular to the joists, and 52 screws per 4 x 8 ft sheet when installed with the long edge parallel to the joists. Even though no one should ever see the subfloor screws, the use of Yellow Zinc plated fasteners will reduce the possibility of corrosion in typical residential applications.

Fixing Squeaks: No discussion of subfloor fastening would be complete without mentioning methods of fixing squeaks. Basically, there are two products designed specifically to help you remove the squeak: Squeak-Relief, a system that pulls the subfloor tight when access is available from below, and Squeeeeek No More, a system using a special break-off screw that installs from above.