I am designing a pavilion roof that will replace the pergola that we currently have.

enter image description here I plan to strip down the pergola roof to just the posts, then rebuild from there. I will place beams to sit on top of the posts, then lay out rafters up from there. The orientation of the gable roof will have the ridge board pointing from where the photo was taken towards the house (vs. the long orientation).

I will use Western Red Cedar to match what we have with the posts today. Based on snow load (30psi in Chicago), dead load (10psi), and horizontal span (11'), the span table indicates 2x8 rafters at 24" o.c..

Here is a top view. Blue = existing posts. Red = planned placement of the beams. Bottom of this image is the house in the picture above. enter image description here

What I don't have a good reference for is, what beam size do I need for the four sides? From this previous post, "4 ply 2x8" was suggested. But, a) "4 ply" doesn't make sense for Red Cedar as far as I can tell, and b) 2" wide is going to look silly on the 6x6 posts (I'd like for it to be at least 4" wide).

Additionally, any red flags come up from experts out there as you look at this?

  • 2
    I believe that a "4 ply 2x8" means four 2x8 sandwiched together, effectively giving you an 8x8. A nominal 2x8 is 1-1/2" x 7-1/2" meaning your four boards will yield you a 6" x 7-1/2" beam. You'll have 1/4" overhang on each side of your 6x6 (5-1/2 x 5-1/2" actual) post. I do not know if Western Red Cedar is sold in nominal dimensional sizes like SPF is, but you could get 6/4 x 8" where "6/4" is actually 6 @ 1/4" (1-1/2" actual size).
    – FreeMan
    Commented Oct 4, 2021 at 18:40
  • Ah, thanks for that! Do you know if it's preferred to stack them horizontally or vertically after assembling them?
    – Jason S.
    Commented Oct 4, 2021 at 19:46
  • 2
    They always go vertically! The 2x dimension is horizontal, the larger dimension is vertical.
    – FreeMan
    Commented Oct 4, 2021 at 21:20
  • 1
    beside each other horizontally standing vertically.
    – Jasen
    Commented Oct 5, 2021 at 11:08


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