How Should I Backfill My Pole Building Holes

This is a subject which is repeatedly brought up. Usually it is ones who are constructing a post frame building which was not designed by a registered design professional (RDP – architect or engineer). The wrong answer could easily lead to a catastrophic failure of the building!

Reader JOE in ROCHESTER writes:

“I am in the process of building a relatively small pole building. 16x24x8. I’m having trouble finding the right answer to the back filling the pole question. The local Inspector will be coming to measure the depth of the holes (42” to the top of the footer) but other than that they didn’t give me any spec on back filling or diameter and thickness of the concrete footer. My question is what do you recommend for footer size and how should i back fill the holes around the poles? 42” of concrete around the poles seems like excessive to me and just back filling with earth doesn’t seem right either. Any advice would be much appreciated. Thanks.”

Mike the Pole Barn Guru advises:
My educated guess is the local building authorities issued you a permit to construct without requiring you to submit engineer sealed plans. All this ends up doing is leaving things to chance – which you are quickly finding out. Column embedment (depth and diameter of the holes), thickness of concrete footing, concrete collars, etc., are a function of many different variables.

Among these variables include – the soil bearing capacity of the earth at your site, weight of building with a code minimum snow load, design wind speed and exposure, building eave height and roof slope, is it fully enclosed, roof only or some or all of a wall open? Any one of these could affect the outcome.

Ultimately you should have a registered professional engineer or architect design the column embedment for you. From judicious experience, assuming a fully enclosed building with wind rated doors and properly tied into a four inch nominal concrete slab on grade, your engineer would probably require these as minimum: eight inch thick 18 inch diameter concrete footings. Two sticks of 1/2″ diameter rebar driven through the lower portion of the column, one each direction and sticking past the column four to six inches each side. A Concrete bottom collar probably 10 inches tall and the same 18 inch diameter, with the balance of the hole backfilled with compactable materials well compacted.