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.

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.

  • Working Time 6 Hours
  • Start to Finish 6 Hours
  • Difficulty         Projects Kind of Hard
  • Involves Carpentry Skills, Sawing, Drilling

What you need

Tools

  • Shims
  • Drill
  • Framing square
  • Measuring tape
  • Pencil
  • Circular saw
  • Layout square

Materials

  • Screws or nails
  • 1X4 beam
  • Joists
  • Ledger
  • Joist hangers
  • Skewed joist hanger

How to do it

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.

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