I am planning to build a corner pergola over my deck. Pergola is 8ft long from the corner on either side forming a triangle on the top. I have used four 4x4 posts (8 ft) attached to the deck headers using three 1/2" carriage bolt per post. How do I reduce wobbling when shear force is applied to simulate wind condition?

Since I am new to the forum, I am unable to post a picture. Imagine it's triangle with two beams parallel to the side of the deck forming a 90 degree angle and the third beam joins these two beams to form a triangle. Third beam has no supporting post. On top of the triangular beam, I have notched joists.

  • 2
    fwiw, any one can post links to photos
    – mike
    Commented Aug 21, 2013 at 20:22

1 Answer 1


You need to install knee braces every where you can. (The diagonal piece)

enter image description here

Ideally, the ends should be tightly dadoed a small amount into the beam and post to minimize the inevitable play that develops in connections made solely of mechanical fasteners. The bigger the brace the better, within reason. The best bracing would be the grand-daddy of knee braces-- X-bracing.

  • Thanks for your response. I can add knee braces for the posts that are installed parallel to the deck edges. However, I do have attaching any braces for the third side of the triangle (diagonal piece). Here is a sketch for your review. Clearly, I have problem in attaching images..
    – user14655
    Commented Aug 22, 2013 at 14:11
  • Here is a link to my pergola sketch. Please suggest bracing for the triangular side of the beam. dropbox.com/sh/ayemiqva1danupy/MITSXu9F2B
    – user14655
    Commented Aug 22, 2013 at 21:14
  • The cut on the knee brace needs to be a compound cut. Not only the 45 deg. of the brace, but the saw needs to be leaned over the complement of the angle to the post so that the brace end mates flat against the post. The cut face on the brace will be much wider than the post, so the sharp end needs to be trimmed off to get the widths to match. I hope that makes sense, I tried drawing a sketch but couldn't produce anything that looked right :(
    – bcworkz
    Commented Aug 22, 2013 at 23:37

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