How to Add an Angled Corner and Joists to a Deck Frame

Building a deck on a sloped site? You'll need to know how to add angled corners and joists to the deck frame. We'll show you how.

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If you're building a deck on a sloped site, you may need to use angled corners for the frame. The angles make it more difficult to lay joists and give your deck the support it needs, but it's not an impossible task. We'll walk you through the entire process—from leveling the beams to attaching joists.

Everything You Need to Know About Building a Deck

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What You Need

  • Shims
  • Drill
  • Screws or nails
  • Framing square
  • Measuring tape
  • Pencil
  • 1x4 beam
  • Circular saw
  • Joists
  • Ledger
  • Joist hangers
  • Layout square
  • Skewed joist hanger

Step 1: Level the Beams

The joint where the two beams meet doesn't have to be tight, but the two beams must be on the same level. Wedge a shim above the post of one beam, if necessary. Drill pilot holes and drive screws or nails to fasten the beams to each other.

Step 2: Mark the Angled Cut

Assemble the outside frame as you did when you laid out the deck, set it on the beams, and attach the rim joists to the ledger. Check for square, then anchor the rim joists to the beam with screws.

To mark the angled cut line, measure out from the corner an equal distance in both directions. Align a straight 1x4 with both measurements, and mark the header and the rim joist. Transfer the marks to the faces of the boards with a square.

Step 3: Cut Header and Rim Joist

Use one of the temporary supports that you made for marking the layout to hold up the header; the rim joist rests on a beam. Set a circular saw at 90 degrees and cut the header and the rim joist.

Step 4: Cut to Fill Corner

Measure between the cuts on the header and rim joist and cut an angled piece to fill the corner. Hold the angle-cut piece in place and drill pilot holes. Attach it with nails or screws.

Step 5: Cut and Install Joists

Cut and install the joists with the crowns up. Attach joist hangers at the ledger. At the header use joist hangers, or drive screws or nails through the header into the joists. To measure for cutting a joist at the angled section, hold it in place and mark it: Have a helper hold one end up against the ledger so that its bottom edge is close to the top of the ledger. While another helper measures to see that the joist is parallel with the next joist, mark the bottom of the joist. Transfer the mark to the face of the joist using a layout square, and cut at a 45-degree angle.

Step 6: Attach Angled Joist

Even if you have fastened all the other joists to the header by backscrewing or nailing, use a special skewed joist hanger to attach an angled joist to the header.

How to Notch Joists Around Steps

If a set of concrete steps is in the way, notch the joists. Cut a joist to length and hold it in place. Level the joist. Steps often slope away from the house, so there may be a gap under the joist. Mark where the joist meets the top of the ledger. Transfer that measurement to the joist where it crosses the edge of the step. Lay out your cut line between these two points.

Because the width of the joist has been reduced, it must be reinforced. Cut a scrap piece of 2x lumber to rest on a lower step and come up nearly to the top of the joist. Attach the support to the joist with several screws.

How to Work Around an Obstruction

It's common for pipes, vent caps, and other obstructions to stick out of the house at about the same height as the ledger. If a vent falls at the top of a ledger, cut a notch for it. If the vent falls in the middle of the ledger, remove the vent cap and extend the duct by 1-1/2 inches. Use a hole saw to make a clean circular cut in the ledger, fit the duct through the ledger, and reinstall the vent cap.

If the obstacle is in the path of a joist, you'll have to frame around it, as shown at right. Install ledger pieces on either side, taking care that the pieces are at exactly the same height. Install joists on either side of the obstacle, then cut and install a piece of blocking between the joists. Cut a joist to run from the header to the blocking piece.

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