Adding Additional Support to a Deck for Hot Tubs

Determine the location of the hot tub on the deck. Measure the dimensions of a hot tub with a measuring tape. Mark the width of the hot tub on the deck with a pencil

Remove the decking boards between the width marks with a pry bar. Set the decking boards aside.

Dig three rows of three 12-inch-diameter holes between the deck joists with a shovel so the nine holes form a square equal to the width and length of the deck. The holes should be deep enough to extend 12 inches below the frost line.

Place a 12-inch-diameter cylindrical concrete form in each hole, and check the side of each form with a carpenter's level to ensure that it is vertical. Trim the forms to a height of at least 8 inches above the ground with a reciprocating saw.

Pour concrete into the forms, pressing down the concrete with a tamper as you pour to prevent the formation of air bubbles. Slide a section of 2-by-4-inch lumber along the top of the form to smooth the concrete. Set a 4-inch post bracket on top of each form in the center, and insert 4-inch bolts through the bracket into the concrete. Allow the concrete to cure for one week.

Measure the distance from each concrete support to the bottom of the existing deck joists. Cut sections of 4-by-6-inch pressure-treated lumber to these measurements with a circular saw to form the support posts. Stand the posts inside the brackets, drill pilot holes through the brackets into the posts and secure the posts with 4-inch bolts.

Cut six sections of 2-by-6-inch pressure-treated lumber to the width of the deck, and attach these sections in pairs with 4-inch bolts to form the support joists. Set one joist on top of each row of posts. Mark the position of the support joist pairs on the rim joists, and mark the center of each post on the support joists.

Remove the support joint pairs. Attach 4-inch post brackets upside-down on the bottom of the joist pairs at each post mark with 4-inch bolts. Attach 4-inch joist hangers at the marks on the rim joists. Set the support joist pairs on the support posts with the ends inside the joist hangers. Attach the joist hangers to the support joist pairs, and attach the top post brackets to the posts, with 4-inch bolts.

Replace the decking boards with deck screws or nails.