Problem with pergola piers not extending down to frostline


Old 06-13-11, 09:09 AM
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Join Date: Sep 2007
Location: USA
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Problem with pergola piers not extending down to frostline

I am building a pergola in my yard where the frostline is 3 feet. I plan on pouring 12" diameter concrete piers that will extend slightly above ground level to support the 6x6 posts.
I rented a heavy duty towable auger to drill the pier holes and found it was absolutely impossible to get to a depth of more than 1 1/2 to 2 feet because of the tough clay (yes I used water and have drilled through clay in the past). No matter how long I drilled, how clean the auger was, and how much downward pressure was applied, the auger just refused to go past a certain depth on all the holes. Another area of the yard with less clay where I'm building a deck was not a problem.

1. Since the piers will not extend down to the frostline, is there anything else I can to to lessen frost heave as much as possible?

2. Since this is just a free standing pergola not attached to anything else will a bit of frost heave even be that big of a deal? The local building codes have requirements for decks but do not cover pergolas at all.
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Old 06-13-11, 07:02 PM
Join Date: Jun 2009
Location: Cincinnati, Ohio
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Your local building inspector is still going to want the footers to be below the frost line. Clay is a weird thing. I drilled 30 holes for my deck and 46 for my fence and hit maybe 3 or 4 little rocks. I had clay, but it went through. My neighbor who shares a corner of the yard with me said he could only get his fence posts down about 1.5 to 2 ft.

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