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I have just built a 6 foot fence all the way around my property. To finish it offI need to build a driveway gate. The gate will be 15 feet wide and have two swing gate sections. I have used 4x4x8 foot posts buried approximately 26" and cemented.
I was considering bolting two posts together and burying them at the same depth, but I am concerned that it still may not be enough support. The gates will have wheels on the bottom also.
The rule of thumb I know that applies here tells me to use at least 6"x6" posts for wide gates concreted into a 3ft deep hole. By preference I'd go for a single larger post and go deeper than you suggest. You might get away with firmly bolting the two posts together, but I would be wary about compromising on the depth...
Wheels help, but wooden gates are VERY HEAVY. I would definitely use 6x6.
Free tip: I had a fencing contractor build gates for me last year, and they are already warped because they only did diagonal bracing in one direction. Be sure to do an "X" configuration with the bracing.
Would NOT Swing 10' wood gates @ six foot height wooden gate on a six by six doug fir or southern pine treated wood post. If you want to use a wood post for a big gate 10ft at 6 ft high you can, and u should it looks better than steel, but you have to use steel for big spans. install a plate 2" x 1/2" thick along the opposite edge of the gate from the way you want it to swing. Rip a small channel in the post (2"x 1/2" deep) and place the steel (full length) screwed every few inches offset into the post. The steel has to run the FULL Length of the post and if its six feet high it needs to be buried in well-mixed concrete 3 feet deep and you need to make sure that Your Post hole is narrower in diameter at the top then the bottom. if board is 5.5 x 5.5 you need to dig the hole 17" x 17" at the bottom and however wide but less than 15"x15" so that its at least that 17" x17"at 40" down in the ground. Two bags of redimix aint gonna cut it. You need (5) 80lb bags. ( I would throw some metal in the mud and lag some steel or at least big nails into all four sides of the post below grade for the concrete to grab the post. don't forget to put some gravel in the bottom of that 40" post hole for drainage. probably a third rail in the gate frame. you do need a cross brace from the end of the gate at the top down toward the bottom hinges wear it attaches to the post preferably a cross-cut so the load is transferred to the bottom rail right at the corner where it can be picked up by the steel hinges.
You can swing a 6' high 10' gate on a 8"x 6" treated post as long as the 8" is in the direction that the gate will be swinging. You can also bolt two 4x6 together and use them without steel. the post needs to placed so the 7" is in the direction that the gate will be swinging.
I Bury 6×6×12 foot posts 3 to 4 feet deep in 10" hole and fill with concrete. This will leave 8 to 9 feet of clearance under a beam/header that keeps the posts equal distance at top as at bottom. Use the other suggestion provided to keep gate square (tension wire or cross brace) and use some strong hinges (sometimes up to 4 each side). Should be good without wheel!
