What Size Screws Should Be Used to Install Wood Decking?

Screws don't pop out like nails when used for decking and they are easy to remove when repairs are needed, making them ideal to use with wood decking materials. The screw should sink into the framing material by 1 inch or more. Use a larger gauge if the screw is being used on framing members and has to support weight. As for the ideal type of screw to use, stainless steel or Dacron-coated screws resist corrosion and are not much more expensive than steel ones.

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Screws should sink about 1 inch into the deck framing.

Deck Framing

The rim joists of the deck are usually connected to the posts and to each other with bolts, but large diameter screws, called lag screws, also can be used. These screws should be at least 1/2 inch in diameter if they will support the weight of the deck, and the point should sink at least 1 1/2 inches into the stationary member. Thus, 4 inches would be the minimum length of a lag bolt used to attach a 2-inch board.

By the same token, 1/2-by-6-inch lag screws should be used to attach railing posts to the rim joist since the railing is a safety feature that may have to support weight in an emergency. Lateral joists are often hung from the rim joist by means of joist hangers; 6-gauge 1-inch screws are suitable for attaching these.

Decking, Railings and Stairs

Most decking screws are 8-gauge and, while 2 1/2 inches is the minimum length needed to hold decking boards to the joists, 3-inch screws are commonly used to provide extra holding power against the upward pressure of shrinking or warping boards. Specialty decking materials have different requirements. For example, Ipe decking is extremely hard and should be installed into predrilled pilot holes with 10-gauge screws that have smaller heads that can be sunk into the surface.

Use 3-inch screws to attach railings to posts and stair treads to stringers, and 2 1/2-inch screws to attach railing balusters. Stair risers and decking fascia made of 1-inch material should be attached with 1 3/4-inch screws, but 1 1/2-inch screws are usually sufficient for these nonload-bearing, decorative boards.


Chris Deziel

Chris Deziel

Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.