I'm planning on building a two-post freestanding pergola in my back yard. I designed it myself with some input from my engineer father, and here are the basics:
Two 6x6 PT posts extending to 7'6" above ground, placed with 12'8" between them.
2 2x8x6' sideways beams, one at the top of each post
4 2x8x16' longway beams (the span between supports is 12'8")
16 2x2x6' rafters
2x4 angle braces at all the corners
I've attached a few pictures describing the design. Note that these are from a slightly out of date rendition -- the long beams will actually extend an extra six inches on each end than what's depicted here.
I guess my main questions are:
1. How deep do I need to sink my posts? I have 10' posts but I'm a little worried that I should have gotten 12', since I've seen some articles online saying the posts should be sunk 1/3 into the ground. With this current lumber they'll be 2'6" into the ground, which is 1/4 the total length (or 1/3 of the above-ground length). Is this sufficient? If it makes a difference, I live in the LA area and there's no danger of the ground freezing any more than occasional surface frost.
2. All my lumber other than the posts is heartwood redwood. Are my beams sufficiently big, or will 2x8s sag significantly over that distance? I'm planning on growing grapes on this, so there will be more weight to support beyond the weight of the wood.
3. Does anything else jump out as being weird or incorrect about my design?
I would really appreciate any and all feedback on this. Thanks!
Two 6x6 PT posts extending to 7'6" above ground, placed with 12'8" between them.
2 2x8x6' sideways beams, one at the top of each post
4 2x8x16' longway beams (the span between supports is 12'8")
16 2x2x6' rafters
2x4 angle braces at all the corners
I've attached a few pictures describing the design. Note that these are from a slightly out of date rendition -- the long beams will actually extend an extra six inches on each end than what's depicted here.
I guess my main questions are:
1. How deep do I need to sink my posts? I have 10' posts but I'm a little worried that I should have gotten 12', since I've seen some articles online saying the posts should be sunk 1/3 into the ground. With this current lumber they'll be 2'6" into the ground, which is 1/4 the total length (or 1/3 of the above-ground length). Is this sufficient? If it makes a difference, I live in the LA area and there's no danger of the ground freezing any more than occasional surface frost.
2. All my lumber other than the posts is heartwood redwood. Are my beams sufficiently big, or will 2x8s sag significantly over that distance? I'm planning on growing grapes on this, so there will be more weight to support beyond the weight of the wood.
3. Does anything else jump out as being weird or incorrect about my design?
I would really appreciate any and all feedback on this. Thanks!