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"rule of thumb" for post install

Discussion in 'Installation Equipment & Techniques' started by Enola, Oct 17, 2019.

  1. Enola

    Enola Member

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    I know there are many variables, but what is the general rule of thumb for above ground vs "In Ground" on support post? Lets talk a 4x8 sign, on 6x6 post, where the top of the sign face (4'high way) would be 12' above ground. How much would your typically have in the ground?

    I have seen this a few times on here, but can't seem to find a thread where it is mentioned.
     
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  2. signman315

    signman315 Signmaker

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    It's based on the frost line for your area and the size/nature of the sign...upstate NY would be 3'-4' in the ground on a 10'-12' pole for a post/panel sign....meaning on a 12' pole, top of pole would be roughly 9' out of the ground. Dig the hole, set the post(s), back fill with dry set cement.
     
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  3. WhiskeyDreamer

    WhiskeyDreamer Professional Snow Ninja

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    Like signman315 said, you have to break the frost line for post installs. So it depends on where you are. I'm usually between 30" - 36" for in ground installation.
     
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  4. Gino

    Gino Premium Subscriber

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    So, you wanna put a 32 sq ft sail 8' outta the ground ?? That's kinda high, but even where we're at, the frost line is 18" to 20" and we'd put that size about 48" deep, in concrete. You'd probably want about a 12" to 16" diameter, with that.

    Actually, most places now require engineer drawings in addition to permits for installations such as that. That's where you'll get the real deciding factor.
     
  5. Pixels Are Bad Mmmkay?

    Pixels Are Bad Mmmkay? Very Active Member

    We are in Central Illinois and the frost line in our region is 36", so we always go 42" to be safe.
     
  6. Pixels Are Bad Mmmkay?

    Pixels Are Bad Mmmkay? Very Active Member

    We ordered a pre-engineered aluminum post and panel sign frame a while back for a local Community Center that was a customer installed job. The design proof I sent them showed the 96" x 36" sign mounted between two 4" x 4" x 1/8" x 9 foot aluminum posts buried 42" underground with 5' 6" remaining above grade and the bottom of the sign sitting 2' 6" above grade. I showed them a typical post and panel proof showing a 6' man's silhouette standing next to the sign for size comparison.

    A few weeks later, the customer picked up the sign and frame and proceeded to install it. I drove by a few days later to check on their progress and they decided it was a good idea to mount 4" x 4" treated lumber in the ground with large, ugly round concrete footings surrounding the posts about 18" above grade. My guess is they wanted to make sure vehicles didn't back into the sign on accident and damage it. As you probably already guessed, they dropped the aluminum posts down over the treated posts, screwed them into the posts with self-tapping screws and called it a day. Not only does the darn thing look like a billboard and isn't all that visible from street level because the bottom of the sign is now standing 7' 6" above grade, but it's like a big sail just waiting for 70 mph winds to rip it clean off the posts or snap the posts off completely. The sign's been up for a few years now with no issues, but someday I feel that their decision to completely disregard the intended installation method is going to bite them in the arse.
     
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  7. TimToad

    TimToad Very Active Member

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    This site is helpful for doing some initial calculations on installations. Every jurisdiction has its own set of rules, but at least you can plug in most of the factors and see roughly what size posts, hole size and depth. Wind speed, building density, etc.. can be found online.

    https://www.engineeringexpress.com/
     
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  8. signman315

    signman315 Signmaker

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    That's my favorite pet peeve! Seems like some people just want to get professional advice so that they can feel special by ignoring it! Little off subject here, but kinda related...I love it when I send them a design sketch that I'm very happy with, and they like it but can't make up their mind, inevitably asking "well what do you think?" My initial reaction is to rip their head off and say "well obviously I'm happy with it, I designed the f****** thing and wouldn't have let you see it unless I thought it was the cat's meow" but instead I calm myself and politely explain why it's a good design that will meet their needs. Kind of like your situation "how deep should we install it?"...."42 inches"...."OK thanks we are going to go with 18".....ahhhhhhhhhhh!
     
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  9. Enola

    Enola Member

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    I understand about the frost line. Rule of thumb around here is 36".

    I'm not sure if it was 1/3 of the entire support post should be in the ground.

    ie. To achieve an above ground height of 12 ft would require an 18' post (2/3's above ground, and 1/3 in concrete. That being 6 ft)


    OR, 1/3 of the "above ground" height ( let's stick with 12 foot) would call for 48" in the ground. (Thus using a 16' post).
     
  10. Texas_Signmaker

    Texas_Signmaker Very Active Signmaker

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    I go 36"... OR until I get too tired to dig...
     
    Last edited: Oct 17, 2019
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  11. ams

    ams Very Active Member

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    Most of my standard installs 4X4X10's are 24" which is standard in Virginia. I may go to 30" for 12', but never had a single problem with 24"
     
  12. Nick Nie

    Nick Nie Member

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    We just did one project, we are in Canada, I feel the best way is to have a engineering drawing, if not, our city require to have 4' deep for 6x6x12' post, AND the post has to be Douglas- Fir grade 1 which is harder to find and more expensive. we just installed a 36"H by 80"w sign.
     
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  13. TimToad

    TimToad Very Active Member

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    We just went 9 rounds this summer with our city's top planner who seems to be on every single builder, contractor, etc. hate list. Our beef was over a 4'x8' post and panel sign whose height to the top of the sign was 7' above grade. He made us dig 24" wide by 36" deep footings and use 6"x6" treated posts for the sign. It took 30 bags of concrete. The client is a preschool and he made them tear down a ramp to the backyard they built and rebuild it because the decking boards were 1/4" too long. This guy's reputation is legendary and not in a good way.

    I'm sharing this to warn others who might use the engineeringexpress.com site I recommended in an earlier post in this thread to be aware that at the bottom when selecting posts, the DEFAULT size footing is 24"x36" even if your installing an 18"x24" yard sign. You'll still get an green light on smaller holes and posts, but you have to manually enter them to test the math on it.

    This planner plugged in our particulars into engineeringexpress.com, refused to manually enter a smaller footing or 4"x4" posts and refused to budge. I guarantee there isn't another similarly sized sign in our entire town that has that kind of support.
     
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  14. Gino

    Gino Premium Subscriber

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    I know the toad can't see this, but his post reminds me of something which happened here many many years ago and may help or give notice to others.

    There was a borough, next one over from where we are, which had more stringent codes than any other around. Getting people to adhere to them was almost impossible. It wasn't just signs, it was in other areas, too. They became known as the worst municipality to do business in, regardless of your trade. Here and there they got some suckers to obey the codes/rules and they became the ones all others had to comply to. Now the precedent has been set. So, while it took 5 or 10 years to get it started, now they have a standard in place and you must obey the codes.
     
  15. kcollinsdesign

    kcollinsdesign Member

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    City planners and inspectors are not qualified for and do not have the authority to engineer an installation, nor do they have the necessary licenses and insurance to perform that type of work. The most they can do is request "stamped" engineer drawings, and keep them on file.

    If there is an insurance claim, those documents can be retrieved and analyzed by a qualified, licensed engineer. If it is determined the engineering was insufficient for the load, the contactor's insurance company may have limited liability, putting the liability for damages directly on the contractor. The contractor, in turn, can sue the engineering firm, most of whom are protected by Errors and Omissions insurance (those who aren't covered will have to pay out-of-pocket).

    The purpose of getting a permit is to have this information on file. Without a recorded permit, it may be hard to determine who is liable if damages arise. Most inspectors are helpful, and their advice and suggestions can be valuable, but many have no clue whatsoever regarding engineering principles. In any case, they have no business dictating how a contractor should engineer any kind of project.

    That said, many city planners and inspectors take it upon themselves to act as de-facto engineers. When they do, ask them for stamped drawings to protect your company from damage claims, and while you are at it request a certificate of Errors and Omissions Insurance. If they refuse to issue a permit after submitting all necessary documents, they can be successfully sued in court. Of course, this is impractical, and in most cases contractors will strive to have good relations with their local inspectors. But when they are over-reaching, occasionally they need to be called out.

    Note: In Central Illinois, for a 4' x 8' installed 11' high from grade sign my engineer would call for two 24" holes 48" deep. That is a bit less then a yard of concrete and below the frost line. If I didn't need stamped drawings, I would probably auger two 18" holes 42" deep and use 6x6 treated posts - I know from experience that would be fine (usually about half the concrete the engineers call for, but they usually build in a 2.5x - 3x safety factor). Been in the business for 35 years and never had a footing failure.

    Note 2: In my area, people put up 4x8 construction and commercial real estate signs time with 4x4 treated posts and 2' deep holes, usually adding a bag or two of concrete mix. No permit required. They blow over all the time.
     
  16. signage

    signage Major Contributor

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    IF the drawing is stamped and installed per the stamped engineered drawing the P.E. that stamped it would be the one held liable, or their insurance company!
     
  17. kcollinsdesign

    kcollinsdesign Member

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    Correct, unless some form of malice on the part of the contractor can be proved. This is why architects and engineers carry Errors and Omissions insurance.
     
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