I am looking to build a decking in the corner of my garden. In the corner it’s about 75/80 degrees so not a true right angle. All the examples I’ve seen online talk about building the base as a square using the size of the joists and planks so you just screw them together.

But with a non square I’m assuming I will need to cut the ends of the joists at an angle and also cut planks short in the corners.

Any ideas?

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  • 90 degree corners do make life easy, almost everything you buy is cut at 90 degrees. That corner makes measurements much more important. Will need to decide if you want the decking boards to match the fence line angle or just leave straight cuts and have a small triangle space for each board.
    – crip659
    Aug 26, 2022 at 16:33
  • Could also make a square deck and build/fill in the triangle that is left open.
    – crip659
    Aug 26, 2022 at 16:47

3 Answers 3


I’m assuming I will need to cut the ends of the joists at an angle and also cut planks short in the corners

Yes, that's exactly right.

Welcome to working on anything that's not brand-spanking new.

You will still just screw/bolt things together (make sure you're using proper joist hangers, hardware, etc), they just won't all meet at 90° angles. It will take extra time to measure everything (twice), and each board in one or more directions will need to be custom measured and cut (no cutting in batches), but it's really not much harder than doing it when things are square.


Depends on a few factors. How high is your deck going to be?

One way to do this would be with a beam that is 90 and joists that sit on top of the beam and just cantilever into the portion of the triangle that isn't covered by the beam. The decking can be cut to have an end angle that matches the fence and left long on the other side. Once you've got all the deck boards matching the non 90 you just cut the long side flush to the joist.

If you want the deck as low as possible to the ground then yes you'd use hangers and have your last joist at an angle but the hanger attachment gets tricky though on a super low deck it isn't such a huge deal.


First measure twice

The first plank and the last plank will have different total length. The raw material should have the last plank dimension.

Consider keeping 1/4 inch spacing between the planks and the concrete wall.

Assuming you want the deck to be perpendicular to home. Set the first plank perfectly square to home with 75 dgr cut on the other end. Use that plank to transfer the end of the cut to the beginning of the next cut on new board. Repeat that process

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