Installing Joists

Each deck level has its own set of joists resting on its own ledger and beam. It is not necessary to fasten the two levels together; when the decking is installed, the structure will be stable.

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Screw a temporary cleat to the top of a joist, extending outward about an inch. Rest the cleat on the ledger. Align the joist with the layout lines, install a joist hanger on the ledger, and fasten the joist to the hanger.

Check that the outside joists are square to the ledger. Transfer the layout lines on the ledger to a long 1x4. At the other end of the joists, temporarily attach the 1x4 to the joists so they are spaced correctly.

When the joists are installed and evenly spaced, measure out from the house and mark the top of both rim joists for cutting. Remember that the header thickness will add 1-1/2 inches to the length of the framing, and that the decking will overhang the framing by another 1-1/2 inches. Snap a chalk line between the marks. Check that there is a clear line on top of every joist.

Use a layout square to mark a cut line on the side of every joist. Each cut line must meet the chalk line precisely.

Cut each joist with a circular saw. Vertical cutting is a bit tricky, so practice on scrap pieces first. You may cut freehand or with a layout square or scrap of 1x clamped on as a guide. Cutting down lets the weight of the saw do the work; cut upward if it seems more comfortable.

Cut the header to length -- usually 3 inches longer than the ledger. With a helper, hold it up against the joists and drive 3-inch screws or 16d galvanized nails to attach it to an end joist. Attach to the other joists in the same way. Make sure the top of the header is flush with the top of the joists.

To mark the joists for blocking, snap a chalk line across the top of the joists. Blocking is usually installed midway between the ledger and the beam.

At each chalk line, draw a square line down both sides of the joist. Cut blocking pieces 1-1/2 inches shorter than the joist spacing to fit between the joists. For instance, if joists are 16 inches on center, cut 14-1/2-inch-long pieces. For 12-inch centers use 10-1/2-inch blocking pieces.

Unless you have a special reason to line the blocking pieces in a straight row, install the blocking in staggered fashion to make fastening easier. Drive two or three screws or nails through the side of each joist.