So I’m looking at building a pergola on top of our raised deck off the back of our house. Total dimensions would be 18’x16′, raised 8′ above our deck. Our deck is raised off the ground 4′-6′ due to the slope of the lot, so I was planning on running the posts through the deck to ground, mounted to blocks on concrete.
For layout, I was wanting to have two rows of three posts (6×6 pressure treated brown) with the posts 8’3″ c-c in each row. I was ‘hoping’ to have the two rows 13′ apart from each other. At the top of each row of 3 posts I would mount my 2×8 beams on either side of the post, overhanging by about 12″. I would mount angled braces on each post (one on outside posts angled in, and two on center posts) supporting the beams. Centered on top of the beams, I would mount 16′ rafters, overhanging each end by about 18″. I’m debating 2″x2″ slats on top for additional shade.
I don’t have a drawing, but I have some images that are very similar to what I am planning (from Google). This first one shows the general shape and layout of what I’m planning (two rows of three posts). https://www.ohiohardwoodfurniture.com/upload/images/products/berlin_gardens/pergolas/outback/15×23-outback-pergola-in-ce.jpg
This second image is pretty accurate as to how I am planning on mounting my beams to my posts, as well as the braces on each post (two on middle one in forground and one on corner posts in background). The hardware depicted here is also something similar to what I was planning on using. https://ozcobp.com/wp-content/uploads/2017/10/51768_lifeStyle_0000.jpg
So, a couple questions I have are. Do I run risk of sagging with the 2x6x16′ rafters spanning beams 13′ apart? I tried using this span calculator to help but I was not entirely sure to input for all the parameters. https://www.awc.org/codes-standards/calculators-software/spancalc
I think it may be using data for rafters that have a load of sheathing on it? Not entirely sure…
Another question, the beams I am mounting to my posts, I cannot seem to find a 2x8x18′ length.. So I was hoping to split each beam into two, using four 2x8x10’s and butting them together on each side of the post supported with some type of hanger. Am I going to run into any issues with this?
Thanks for any input.
Replies
I have a deck pergola with 2x6 on 12" centers, spanning 10 feet. I could have designed it for 16' span, but I designed a beam to go under them at 10. 16' seemed to me to have too much potential for sag. I also couldn't find documentation on it.