Cantilevering a Deck

Double-check your stamped deck plans to make sure the cantilever, or length the joists project past the beam, is half the length or less of the back span, which refers to the distance between the ledger attached to the side of your house and the support beam. Also double-check that the cantilever is no more than 3 feet long in total if you are building a deck with regular 2-by-8 joists at 16 inches on center. Longer cantilevers require larger joists or joists placed more closely together.

Dig holes and install sonotubes -- cylindrical cardboard forms -- at the points indicated for support posts on your deck plans. Pour concrete to hold a J bolt in the center and allow the concrete to set. Bolt a 6-inch post base onto the J bolt.

Nail 6-by-6 posts through the sides of the post bases with galvanized nails. Mark them level with the top of the ledger by running a straight 2-by-4 topped by a spirit level from the top of the ledger to the post. Mark down the post to account for the depth of the beam (for example, 9 1/4 inches for a nominal 2-by-10 beam). Mark down still farther to account for the depth of the joists (for example, 5 1/2 inches for a nominal 2-by-6 joist). Cut the posts level with the lowest mark with a reciprocating saw.

Construct a beam out of doubled or tripled 2-inch dimensional lumber according to your architectural plans. For example, a large deck may have three 2-by-12s bolted together. Drill a pair of holes every 3 feet along the beam with a paddle bit and press 1/2-inch galvanized lag bolts through the holes. Ratchet a nut and bolt onto the end of the bolt and tighten the nut.

Nail post-beam caps with galvanized nails to the top of the posts. With the help of an assistant, lift the beam into the post-beam cap and nail through the cap into the beam.

Nail joist hangers into either end of the ledger and 16 inches on center in between as shown on your plans. Cut joists with a chop saw to the length called for in the plans and drop them into the joist hangers so that they rest on the beam and their free ends project past the beam, creating the cantilever. Nail through the joist hangers into the ledger end of the joists.

Mark the beam with the positions of the end joists and the positions of the intermediate joists at 16 inches on center. Line up each joist to its correct position on the beam. Nail hurricane ties into the joist and the beam.

Cut a rim joist to run across the free ends of the regular joists. Hold the rim joist in place with quick clamps or bar clamps, or with the help of an assistant. Press joist hangers under the ends of the joists and against the rim joist. Nail the joist hangers to the rim joist and the regular joists. You’ve framed your cantilevered deck and can finish its deck boards, railings and balusters per standard deck techniques.