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I wanted to know if I would possibly have any issues with the Pergola Sagging for the 2x6x16 Girders? I plan on purchasing Premium Redwood and Mount the girder with 10 Inch Carriage Bolts on 4x4 Pressure Treated Post enter image description here Sent a sample of what I am looking to do from another persons pergola design?

HomeimproverK
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  • Gonna have grapes or other vines/plants, or not? Do you get snow, or not? – Ecnerwal Oct 06 '21 at 23:34
  • If you mean the double joists around the perimeter, they act like beams supporting the floor joists that run perpendicular to them and provide stability in another direction. If you overload beyond their capacity with a noticeable sag, it's everybody's guess what would happen after that. Check with a structural engineer to see whether your proposal is acceptable or not. – r13 Oct 06 '21 at 23:35
  • Define your max allowable deflection and go from there – whatsisname Oct 06 '21 at 23:53
  • A 2x6 is, in effect, a very skinny shelf. Go check out The Sagulator to see how much deflection you'll get. To determine the load, add up 1/2 of all the material that will be resting on top of it and pick "Total load". Also, in this pic, the ones running left-to-right won't have any weight on them, the ones running front to back will be carrying the load of the ones above. Odds are good, though, that you won't have much to worry about. – FreeMan Oct 07 '21 at 00:33

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That is a beautiful pergola.

I walked onto a job one day and the man had a two car garage with a flat roof and 2x6s were used to span the 20 feet across both stalls without support. Needless to say, my job was to fix the fact that the roof sagged to the point that the garage doors could not longer operate properly. The customer swore that he had no sagging until the heavy snow load of last winter. We did have heavy snow that year, but the garage was 20 years old. I can't believe it lasted 2 years, but it did ten fold that!

As a rule of thumb, a 2x10 can support a live load across 12 feet (a typical floor) and a dead load requires less support (a roof), but your pergola needs even less because it won't hold snow.

Your question should read: "Will a 2x6 hold its own weight without sagging across a 16 foot span?"

Answer: Make sure you are crown up during install. Realize that the 2x2s on top are more than decorative because they do add structural integrity tying all of the 2x6s together. I know they don't grow trees like they used to, but you're gonna be fine for a long time.

Feel free to copy what you see.

Paul
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  • Thanks for taking the time to Reply Paul and Others. No Vines or anything will be added and No Snow. In in Northern California. – HomeimproverK Oct 07 '21 at 23:12