I have a 6x5 plywood sign 'box' (6'x5'x1')to install over a couple of 6x6 posts. How deep do the posts have to be placed into virgin soil of 6" dirt and clay beneath? If I dug a trench and filled it with concrete, how big? Is there some windsheer guide available?
My hunch is to dig a 40"deep x12"wide trench and drop in the posts, fill with concrete. The frost line here is 39"?
Any help will be much appreciated.
Posted by Jon Butterworth (Member # 227) on :
You don't say how tall the posts are.
The old "rule of thumb" is 1/3rd in the ground.
That is sign 5ft high + post height say 7ft = 12ft Divide by 3 = 48" deep Area sign is 5x7 =35sq ft divide by 3 = 6sq ft divide by two post holes 48" deep = 18" square holes.
So your estimate of a 40" x 12" trench should be more than enough
Posted by old paint (Member # 549) on :
whats the sign weigh that your building? find that out..then make concrete below ground at least wiegh 1 1/2 -2 times more then sign....you also need to figure for every 8-10' in height you will need to add more weight below...not a math major but did build a few buildings....
Posted by Preston McCall (Member # 351) on :
The sign is 6' wide and five foot tall. It will be a monument. Two 3/4" MDO sides with ends and top. No posts will show. Two 6" posts. Plant the posts 36 inches deep, but should I dig a trench and fill with concrete, insted of just the post holes? I figure the added weight beneath the grade and a solid block of concrete will keep the thing planted. Do I have to plant the bottom below the frost line?
Posted by Dave Sherby (Member # 698) on :
In your case, don't bother with concrete. Your wind load will be more than covered by the required depth. Definatly dig below your frost line. The frost will literally push your poles up, as much as an inch a year, and it seldom pushes them up evenly. Instead of investing in concrete, dig the holes a little deeper than your frost line. If your normal frost line is 39", I'd go 48 inches deep. It's called insurance. When you back fill the holes, throw in about a foot of dirt, than tamp the dirt down hard. Repeat till filled.
6x6 treated will easily last 20 years in the ground.
Posted by Jon Butterworth (Member # 227) on :
What's a "frost line" ? Is that the line the hose leaves on the lawn in winter when the ground temperature actually drops two degrees below freezing That's COLD here hahahahahha
Wooden posts? "Wooden" last 3 months here ... we are inflicted termites from hell!
But I agree with Dave ... why bother with concrete? Just take those post holes down 4 ft, especially if its clay. maybe a concrete cap for looks.
Do you know the trick to digging post holes? Dig the first one to the required depth. Dig the second hole close to the same depth allowing for slope. Lay a straight edge between them with a level on it. measure down and adjust depths of the holes to match! Believe me ... if the bottoms of your holes are level .. the sign will be level when you stand it up!
Preston, I have done a lot of building in the KC area over the years. Three feet will work fine on depth for your project. Find an electrical contractor that can set poles and have him auger you 2 holes about 40 inches. Align your posts in the holes and dump a couple of bags of quickcrete(small bags) into the bottom of the hole and hose with water. Fill holes to about 10 inches from the top with dirt, and then pour another couple of bags of quickcrete and wet down. Then cover up the balance with topsoil. When it sets up it should be pretty solid, as it creates a double concrete brace to the solid soil in the surrounds. It is the way that almost all pole type buildings are constructed in the farmlands, with little to no failure. They seldom are installed below 3 feet, though I am familiar with that frost level there. Be sure to use proper creasoted posts below ground and cover the posts for appearance down to ground level. Bronzeo
