View Full Version : post hole depth
Aug. 6, 2010, 11:51 AM
this is probably a dumb question, but for 8' posts, what's the proper depth for the best stability and to make them resistant to heaving in winter? I'm digging 61 holes for a small pasture out at our new place. We don't have any machinery so we finally gave up an hired a guy with an auger. This morning I measured the holes he dug and they're all about 38". I had asked him to dig them 42", or 3 and a half feet. That would leave 4 and a half feet of post sticking out. So - is closer to 3' deep enough for a 5'post?? I'm doing Electrobraid - corners 6" posts and line posts are mostly 16' apart and 4" posts. I'm in SE michigan and the soil is clay with some small rocks and gravel mixed in. Thanks in advance! :confused:
Aug. 6, 2010, 01:53 PM
I can't answer your question specifically but my first thought when I read your post was "if you asked him to go to 42", and they're not, then he's not done." I live in New England so we get real winters etc. I think the ideal is 42", that's at least what I have to have for my posts for the barn. I think at 38" you're probably OK. But I'm not very knowledgable about clay. I am building my barn and the first paddock on ledge so I'm pretty comfortable with anything between 38 and 42", at least for fence posts. The barn posts are at 42" and will be on cement.
Aug. 6, 2010, 02:37 PM
I agree - he's definitely not done. I have a whole separate spate of issues with the guy. He was supposed to start Tuesday and showed up Thursday, dug 4 1/2 holes and left. I left him a message about the depth this morning so we'll see what happens, if anything, today. He was supposed to have them all dug this week so I could install the Electrobraid and charger, etc. this weekend. Last thing I heard from him yesterday besides a bunch of excuses was that he wouldn't be done till Tuesday. I was supposed to move the horses home next weekend and now that's obviously going to have to be postponed. I'd have severed ties already but I just need to get this done and don't have any other options!!
Aug. 7, 2010, 12:15 PM
I was always told to bury 1/3 of the post for the best stability. So for 8' posts (96") they should be buried a minimum of 32".
That will leave you with over 5' of post sticking up.
If you don't want them that high, either bury deeper or as most fence builders do, cut off the tops after installing the rails.
FYI - depending on the equipment your "guy" is using he may not be able to dig any deeper. Our compact tractor could only push the auger 3' down.
Aug. 7, 2010, 12:50 PM
that's what we learned- 1/3 below, 2/3 above ground.
So for an 8 foot post, that would be about 2 1/2 feet below ground- at least 32 inches, leaving a little more than 5 foot above ground. I'd cut them to 5 feet and have a taller fence for my horses- 4 feet is too easy to jump over. We did this 16 years ago and not one of our posts has shifted.
This is for our glacial clay soil with lots of little rocks in it, which tends to hold the posts rather well. Sandy soil may need more, and cemented in posts definietly don't need as much.
Aug. 7, 2010, 10:06 PM
Below the frost line, if you can. Here that means 48". :dead:
Aug. 8, 2010, 04:14 PM
Thanks all - I'm going to try for 42". The guy came back Saturday to pick up his stuff and took off. I think it was too much for him. Guess I better find someone else who can drill pretty deep holes...
Aug. 8, 2010, 05:58 PM
Dave should be back next weekend, so maybe he can help with the post hole digging if that other guy isn't working out. That sucks!
FYI, for whatever it's worth, we dug the 36" at my mom's house with 8' posts. She has sand, and that seemed to work....the posts have lasted for 20 odd years! I would think the clay would be even better for holding the post, but not sure. Also, you probably already know this, but the corners are usually longer and deeper, or cemented in.