I need a little info. I have a sandbox which is 10'x12' and I would like to put a roof over the sandox. I am going to use 4x4's (in contrete) for the main supports and 2x10's for the horizontal span. then I will put 2x8 (16" on center) sitting vertically with a lattus over the top. This is not supporting too much weight. I will have the roof extend 1 foot on each end. This will make the actual roof 12'x14'.
Can I get by with a post in each corner or do I need three supports on the two 14' sides?
What you have is fine: Just add a couple of 45 degree "arms" at each corner to help hold up the middle of the spam. REmember to put the bowed side of the timbers upwards.
The 2x10's are good. Ok for 14' with such a light load.
You could use 2x6x12's for the (10 foot + overhang) flat roof span. There are a lot of single story ranch homes that used 2x6 to span 12 foot for the floor load.
Just make sure you get the posts set to a depth that is below the freeze line for you area, put about 6" of gravel in the bottom of the hole and check the ends of the 4x's for the growth rings. Try to get center cuts. Meaning the more it looks like a bull's-eye, the better you are doing. The more off center it is, the more likely to twist.
The 45 degree arms mentioned by another poster will add a lot of wind resistance to the structure.
Great! The land in this area is loaded with rocks and digging these are not easy, even with a power auger. Here is the rundown on what I will be doing: I will go 4' deep with the holes, add 6 inches of gravel, put concrete around the posts. The size will be 12'x14'. I will use double horizontal (2" x10"x14') supports across the 14' span. Then I will install a cantilever support on each horizontal support. Next I will put 2"x6"x12' boards on end
24" on center. Then top the entire structure with lattus.
Does this sound good to you? Since these are not load bearing I figured 24" on center should be fine.
You know your "freeze depth" better than I. Around here 2.5' would be deep enough.
According to the data in my span table, #2 2x6's used a ceiling joists supporting 2 lbs. per square foot of drywall are good for an 11' span when spaced on 24" centers and 13.75' when spaced on 16" centers. The lattice weighs considerably less than drywall.
I would be more concerned about the lattice bowing/sagging on the 24" centers. It is designed for vertical applications. It is only going to cost
4 extra joists to do it on 16" centers. And then when the wife wants to plant and train a vine to cover it, you will have the structure to support the extra weight.
BTW just in case you don't know, the footprint is square (the four posts) when the measurements of the diagonals (think big X) is equal. The more time you spend getting the posts laid out square the easier the balance of the project.
If you can, post or send me a picture when done.
Colbyt
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