What Size Plywood for an Attic Floor?

Plywood

• Plywood is a type of wood sheeting that contains pressed wood particles. This man-made product uses strong adhesives and mechanical pressure to create a material often stronger than wood in its natural state. Plywood is a versatile construction product that resists warping, shrinking and twisting. It comes in a variety of lengths, widths and thicknesses. The grade of plywood refers to the surface finish.

Minimal Use

• If you only use your attic for occasional storage, you don’t need heavy-duty plywood for your flooring. The most common thickness of plywood for use as flooring in attic storage spaces is 1/2 inch. Sheets generally come in 4-by-8-foot lengths, making them easy to transport and maneuver into the attic space. These thin sheets are suitable for attics floors above ceiling joists set on 16-inch centers. Older attics with joists set on 24-inch centers require 3/4-inch plywood to provide a sturdier flooring surface.

Regular Use

• Create a sturdy floor for an attic that experiences regular foot traffic. This live load requires 3/4-inch tongue and groove plywood. The tongue and groove construction of the plywood adds an element of flex, allowing the flooring to accommodate the weight of footsteps. This helps protect the underlying ceiling from stress that can cause cracking and chipping.

Precautions

• Proper installation is as important as choosing the correct size of plywood for the attic flooring. Make sure the edges of the plywood meet over the centers of the ceiling joists. Install plywood sheeting in your attic so the grain of the plywood runs at right angles to the underlying joists to create the greatest flooring strength. Attaching the plywood with screws, rather than nails, helps prevent cracking and chipping of the ceiling below the attic flooring.