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In this thread, our forum members can't come to an agreement on whether or not concrete is an adequate material to support wood fence posts.
Original Post: Is My 8-Foot Fence Doomed?
Funny how you learn to ask things as you do a project. Anyway, by the numbers:
1) New fence using 4x4 wood posts
2) Post holes are 40 inches
a) 4 in. gravel
b) 36 in. depth for the post itself
c) 8-8.5 in. diameter
3) About 60-ish pounds of concrete per hole, some more then that
4) Mix of clay and gravel tamped into top portion of hole
5) 4, 2x4 rails
6) Max of 8 ft. between posts, average 7-ish
As I said, I haven't put the pickets up yet and I'm just worried that all the passersby who watched me construct this fence over the last 7 weeks are gonna watch it blow over in one.
1) Did I do OK?
2) Should I gap the pickets? (Treated pine that's been in my garage since March stacked neatly, no noticeable warping)
a) If so, how much?
3) Is there anything I can do to strengthen it, or am I out of luck?
Gunguy45 Super Moderator
I think I would have gone with 10"-diameter holes and probably more concrete—the only issue being that the thinner concrete at the corners of the posts is a weak point. I've seen plenty of fences built less sturdy than what you have that have lasted 16+ years.
One thing I'm not clear on...8' posts? So, only 5' above ground? Or 10' posts with 7' above ground? If the former, you should be fine. If the latter, you're probably going to have issues as that's a heck of a wind load.
The posts are about 10.5 long, resulting in about 7.5 above ground. Any suggestions to shore up? Dig around it to pour more concrete on the corners?
Didn't see it mentioned, but does your town permit a fence that high? (Some don't.)
I never use concrete with wood posts. Concrete holds moisture, which rots the posts. The 36" depth is good. However, I don't think that the fence will fall. Bud is right about permits for that height. The inspectors might be worse than the wind.
Permits notwithstanding, you're doing a good job. I'm waffling on Donato's comment about concrete vs. no concrete. I would like to see some statistics or test results about this.
stickshift Group Moderator
Rule of thumb is 1/3 of the post in the ground, which would be 3.5 feet for you. You're close.
I installed many fences with a friend of mine—it was his company. We never used concrete for wood posts. We used it for chain link and PVC posts. Even if you don't think that the moisture from concrete can rot the posts, another reason not to use it is that with high winds, the fence will be less flexible and more likely to snap the posts. We would see more downed trees if they weren't flexible and didn't bend with the wind. Even tall buildings are made to sway.
Thanks for all the replies.
1) It is permitted.
2) I heard about concrete potentially adding to the rot problem. I figured the gravel underneath would help stave that off (at least long enough for me to move).
Gravel helps drainage, but it doesn't add strength.
When it comes to wind damage, it won't make much difference. If the wind is strong enough to snap the post, then it will snap them in plain ground also. However, depending on ground conditions with high winds, using concrete could be a problem. In my location, one section of ground becomes very soft during the spring. Having concrete is a real problem when trying to straighten the post if wind causes them to lean.
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