How to Build an Angled Deck

How to Cut Angles

Installing decking at a 45-degree angle is not difficult. Practice cutting some scrap decking to make sure you can consistently cut a precise 45-degree angle. Measure carefully to see that the first boards are installed correctly, and the rest of the deck will go on quickly.

A radial-arm saw or a 12-inch power miter saw is ideal for cutting 2x6 or 5/4 decking. With a 10-inch power miter saw you may have to finish each cut with a handsaw—a time-consuming extra step. With practice, you can make accurate 45-degree cuts with a circular saw, using a layout square or a jig as a guide. Some circular saws manage this more easily than others; often, the blade guard gets in the way at the beginning of the cut.

Step 1: Prep House

To help maintain a straight line near the house, temporarily attach a strip of 1/4-inch plywood against the siding, on top of the ledger. Make sure the screws you use to fasten the strip are above the decking thickness so you can remove it after you install the decking.

Step 2: Cut Boards

Choose two straight boards and cut one end of each at a 45-degree angle. A 10-inch power miter saw will not cut all the way across the board. Complete the cut with a handsaw. If you are experienced using a power miter saw, lift up on the forward edge of the board to finish the cut.

Step 3: Install First Boards

Set the two boards on the joists with the mitered ends pressed against the spacer strip. Measure from the corner to the edge of the decking in both directions. When the two measurements are equal, the decking is at a 45-degree angle to the house.

Check the first board for straightness and fasten it to the joists with nails or screws. You may drive all the fasteners as you go, or drive only a few at this point and snap chalk lines to line up all the other fasteners.

Step 4: Continue Laying Boards

Attach decking by driving two fasteners wherever a board intersects a joist. Insert a spacing jig between the boards. An automatic-feed screwdriver makes the job go quickly. Set the nail or screw heads slightly below the face of the decking.

Step 5: Mark Overhang

To mark the decking for a 1-1/2-inch overhang, hold a piece of 2x lumber (which is actually 1-1/2 inches thick) under the decking as a gauge to mark both ends of the cut.

Step 6: Make Chalk Line

Give your chalk line box a good shake to make sure the line is well-loaded with chalk. Hook the line onto a nail or screw driven partway into the side of one of the marked boards. Be sure to pull straight up when you snap the chalk line.

Step 7: Cut Edges

With clamps or deck screws, temporarily attach a straight board to the decking to serve as a guide for cutting along the chalk line. Cut the line with a circular saw.

Step 1: Bend and Fasten

If a decking board is bowed, you will need to bend it into place. Insert spacers and fasten one end of the board. Then move along the board, straightening it as you go. Where a board needs persuading, drive a fastener partway into the board, push it into position, and finish driving the fastener.

Step 2: Pry Board

If pushing does not do the trick, dig the point of a chisel or pry bar into the joist, right up against the decking board, and pry the board into position. If a board is so badly bowed that neither of these techniques works, replace it with another one.

Tip: Easy Spacers for Tight Places

Traditionally, decking boards are spaced using 16d nails. To keep the spacing consistent, make a spacing jig. For tight places or short boards, drill a pilot hole through scrap blocks and drive nails through the blocks.

What if You're Stuck with a Small Piece?

If the last piece is large enough, install it as you did the other boards by drilling pilot holes and driving fasteners down through the face of the board. If the piece is small, cut and attach it after making the chalk line cuts. Drill horizontal pilot holes and attach the piece with screws or nails driven into the adjoining deck board. There will be no space between these two boards.