I had a builder put up a raised 10x13 post and beam foundation in anticipation of a shed placement later. I measure it and find the diagonals are 4" off. What is the easiest way to adjust the rhombus back to square? Do I add a shim piece to the 6x6 posts on opposite corners?enter image description here

*Edit: Attaching another image to show exagerated shape and diagnals. Also the 2x8 attached to the posts with lag bolts enter image description here

  • Hello, and welcome to Home Improvement. You mean, measuring the two horizontal diagonals gives you different values? (Please add some clarification to your question; thanks.) May 14, 2019 at 18:28
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    Call the builder and ask them to correct their error at their expense.
    – Ecnerwal
    May 14, 2019 at 18:33
  • Impossible to say without knowing more about the framing. Please post photos or a more accurate description of the connections to the posts.
    – isherwood
    May 14, 2019 at 19:33
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    And technically it's not a rhombus since the sides aren't equal. It's a non-rectangular parallelogram. </pedantry>
    – isherwood
    May 14, 2019 at 19:35
  • For clarification, the framing is attached to the sides of the posts using lag bolts and not sitting on top. The long sides are parallel also.
    – user101603
    May 14, 2019 at 20:44

1 Answer 1


Assuming that the sides are parallel, since you called it a rhombus, and the framing is attached to the sides of the post as the drawing seems to show: You can definitely add shim pieces to the posts on the side that is at the top and bottom of your drawing. Depending on the load that the fasteners take, You may need to attach a block of some sort to support the end of the joist, since it won't be properly attached to the long side anymore.

You could also frame the walls square, and have them overhang the short corner.

Ideally, you should not finish paying the builder until he fixes it.

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    You can't "definitely add shims" without knowing something about the framing. If the flush beams are on top of the posts, shims do nothing. If there's building hardware involved, shims are also probably not an option. We need more info.
    – isherwood
    May 14, 2019 at 19:39
  • Added another qualification to my answer to clarify my interpretation of the drawing. It appears to show framing on the sides of the beams, not the tops.
    – Valkor
    May 14, 2019 at 20:04
  • I've seen other suggestions to just frame it square on top of the foundation. With 2x6 footers I guess it would only overhang by a small amount.
    – user101603
    May 14, 2019 at 20:47

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