Dear Guru: Should I Use Concrete Sonotube Foundation?

Pole Barn Guru Blog

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: I am planning to build a post-frame house 32×40. I built a 16×16 post-frame barn last Summer as practice and found that I hit bedrock at 2 to 2.5 feet. I know that most post-frame buildings require a 4 foot hole with a concrete footing to keep the post from settling, while also providing lateral strength. I don’t seem to need the depth for settling issues since I’m building on bedrock, however, I lose the lateral strength of a deeper hole. Is there a way to add lateral strength? Also, since I’m not getting that support from a deep enough hole, would it be better to use a concrete sonotube foundation with sturdi-wall brackets to mount my posts?

Thank you – DIGGING IN DOVER

DEAR DIGGING: If you think about it, a sonotube filled with concrete and a bracket on top, is going to provide less lateral resistance than a column in a hole filled with concrete. Depending upon building dimensions, exposure to wind and soil conditions above the bedrock, it is very possible increasing hole diameter and using a complete concrete encasement could do the trick.

As you firm up your plans, we can provide a preliminary hole layout. From this, you can dig the holes and give an exact measure to what point solid bedrock is encountered. This will allow for a design to be created which will minimize the amount of digging and concrete, without negative effect upon your structure.

DEAR POLE BARN GURU: 30×48 pole bldg. was just completed. The 4×6 posts were set on cement cookies 16″ x 4″ every 8′ and then packed with dirt. Is it too late to remedy this situation? Should I dig down to each cookie and pour some cement to encase each post?  The bldg. was just completed last week, so dirt is still freshly packed. What do you suggest? EVENTFUL IN EVANS CITY

DEAR EVENTFUL: It is not too late, but it will involve work which could have easily been avoided. The concrete cookies are not going to be adequate to prevent settling and they do nothing to prevent uplift.

I’d start digging. Make sure the bottom of the hole (directly above the cookie) ends up larger in diameter than the area closer to the surface. You should probably go to two foot diameter and then pour at least 18 inches deep of premix into the hole.

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