How to Curve a Deck

Install a ledger on the side of your house, held by lag screws driven into the rim joist above your house foundation. Pour concrete bases for support posts into forms and install a beam atop the posts, held by a connector nailed by galvanized nails. This process follows standard procedures for building a rectangular deck.

Nail one end of each joist into a joist hanger on the ledger. Nail a hurricane tie in place to connect the joists where they rest near their midpoint on the beam. Allow the joists to run slightly longer than the lengths designated on your plans so you can cut them into the arc of the curve.

Nail a 1-by-4 brace across the joists at the point where the plans call for the curve to commence. Measure from the insides of the outermost joists, divide by half, and mark this spot on the brace. Nail a long 1-by-2 at one end to this marked spot so that board can rotate and allow you to mark a half-circle on the joists. Drill a hole at the point representing the circle’s radius. Insert a pencil in the opening and twirl it across the joists to mark the arc.

Measure the angle of each pencil mark -- it will be different for each joist -- with a protractor and mark it on the joist. Extend the cutting line down the front and back of the joist, set your circular saw to the angle noted and marked, and bevel the joist along a clamped piece of scrap wood to guide the saw smoothly. Cut the joist with a reciprocating saw instead if you have an acute bevel that your circular saw cannot handle, recommends “Advanced Deck Building.”

Create a rim joist to wrap around the ends of the joists and establish a curved frame. Mark the rim joist -- typically 2-by-8 or larger piece of dimensional lumber -- with lines an inch apart to serve as guides to create kerfs, partial cuts just 1 1/8 deep that allow you to bend the lumber. Cut the kerfs with a radial arm or circular saw set to the correct depth. Soak the rim joist in water for two hours so it will bend even more easily.

Screw the rim joist to the ends of the beveled joists. Where the rim joist meets the straight outside joists framing the rectangular area of the deck, butt joint the rim joist to the outside joist after first nailing blocking -- pieces of scrap joist material that run perpendicular to the joists to strengthen them -- behind the spot where the butt joint falls.

Screw deck boards on the rectangular area of the deck first, with two screws per joist. Dry fit deck boards on the curved area and gently nudge them if need be to avoid having a final deck board that is a narrow sliver. Scribe the underside of the deck boards with a pencil, using the rim joist as a guide. Flip the deck board over, cut the scribed line with a jigsaw and return the deck board for screwing in place.