Had the math sorted previously but now I'm hoping to simplify. I'm hanging three sails -- a 12 x 12 square, then a 12x equilateral triangle, then another 12 x 12 square. The far ends will be attached to the house to studs through the exterior wall. The near ends will be attached to 6x6 12' timber posts sunk in 12" x 4' holes with concrete, for 8' of exposed post.

I was originally going to use four posts but my question is: can I use a single 6x6 in the middle to support one end of the triangle and one corner of each of the squares so that I need only three posts? They'd be anchored to three of the four faces of the post.

Thanks in advance!

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There is no real reason that would prevent you from getting by with just three of the 6x6 timber posts as long as you make sure that the lateral pull on the pole 8 feet above the due to stretching the shade sails tight does not pull the post over. This lateral force will be highest on the common post that takes the strain from multiple sail pieces.

Some considerations to think about:

  1. If all the sail pieces are installed at the same level more posts may make it easier to get the edges of the adjacent pieces to line up edge to edge.
  2. If you were to make the triangular piece larger by some amount and then installed it a level a few inches above the square pieces you could get overlap with a pleasing look.
  3. If there are problems with the lateral stress on the tops of the posts you may need to consider installing guy cables down from the posts out to an anchor in the ground OR install wooden members as struts from the post tops back to a ledger board on the outside surface of the house.

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