Post Frame Footing Size

[MIsparkz]

Wondering what size concrete footing you guys have to put under your pole barn posts? I know it's going to vary drastically with soil types, snow load, and obviously barn size. I'm looking at putting up a 30 x 40 and need 30" footings and 36" under the poles on either side of the overhead door. Seems my county has little more excessive footing code than others around here since every builder I have talked to has a hard time believing it. Most have said the only thing they ever use is the 16" preformed cookies.

 

[oldtinsmith]

I had to use 4" thick by 14" round "cookies" resting on undisturbed soil (heavy clay here) and below the frost line of 42". My 40' long (20' at 24' deep and 20' at 30' deep) by 10' high pole building.


Doug

 

[MagKarl]

You can do a rough check yourself. Do you know your county snow load design value? What about your soil type? Search "soil bearing capacity" for some values. Clay in my area is figured at only 1500lbs/sf. which drives big footings. See if the footing size makes sense for your post load and soil capacity.

 

[brownbagg]

i thought the whole idea of pole barn was to drive some telephone poles in the ground like piling and then wall it in. my idea of pole barn was no foundation or footers

 

[RPH]

I had to have 20" diameter and keep that 1 foot high. Also down 42".

 

[Flexia]

Around here a 16" pad used to be code 36" down. Now its 24" poured pad 1' think 4' down.

 

[MIsparkz]

Here's the formula my county uses and claims it's based on Michigan's 2000 residential code:
((1/2 of truss span + roof overhang) X (roof live loads + dead loads) X pole spacing) + wall load= total load on footing
I have 30' span with 1' overhang so it's 16 x 40 (35 snow and 5 dead load)=640
Poles are 8' on eaves except for overhead door poles. 640 x 8= 5120
Plus a wall load of 1 the building department said. (Typical government formula where you are dealing with numbers in the thousands and they want you to add 1 for wall load like that's going to make a huge difference!)= 5121psf

So I have 5121psf on each post and according to their supplied chart in clay a 24" hole is only good for 4713psf so I have to go to a 30" which is good for 7364psf. My two poles on either side of garage door need a 36" hole since it's a 16' span. I haven't seen anywhere on the documents they gave me on how thick the 30" diameter pad has to be. I'll have to call and find that out and also ask if I get a engineered plan from a polebarn package place that has stamped plans with smaller footings shown is that good or is it their way or the highway?

Everyone that I have talked to about barns thinks it's ridiculous. So it's not the norm around here. That's why I was wondering what other locales require.

 

[MIsparkz]

Oh and yes top of the concrete has to be 42" below grade.

 

[oldtinsmith]

I was very careful to make sure I got all my permits, got my plans date stamped and signed. Before I bought my pole barn package, I had made many stops at the township offices and asked alot of questions of the building, electrical and plumbing inspectors. They were very helpful and appreciative of me wanting my barn built to code (I didn't want a code violation to keep my insurance company from possible not paying a claim if something happened!). ... The township offices are at best 1/10 0f a mile from my house and the inspectors drive down the road I live on every day they are in their office !

Doug