John, I9m near you in northern Washtenaw county. My problem is I9m on a
small lake and the water table is down about 2 feet. The code now requires
pilings and the cost is 15-20K, way more than I want to pay. If the
structure is less that 400 sq ft, you can do pretty much what you want. My
70 year old cottage sits one footers down about 2 feet with a little cement
and a mortared stack of cinder block. It9s held up pretty well. Not much
shifting. The footings are somewhat shielded from the elements, although I
suspect is was not heated most winters. I9m thinking of a crushed limestone
floor, I mostly want to park my boat or a car or two in the winter. And then
a pole barn type construction. I was thinking maybe a 3flat2 2 x 29 rebar
enforced concrete pad a few inches thick down about 29 might do the trick.
But, I9m sure open to ideas.
Brian
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From: Briggs John F <jfbriggs@sbcglobal.net>
Date: Thu, 31 Jul 2008 21:12:11 -0700 (PDT)
To: "Brian C. Kennedy" <kennedybc@comcast.net>, Team shop-talk
<shop-talk@autox.team.net>
Subject: Re: [Shop-talk] Pole barn and deck footers
Brian,
It kinda depends on where in Michigan. Building Code in Southern MI ( I'm
in Livingston County) requires the the top of footings for pole building and
deck footings to be at least 42" below final grade. Northern MI would be
deeper. You can look up the normal frost line in your area on the internet.
The top of your footing can be at that level, but your county probably has a
minimum depth. You can make it less than that, but you should then expect
things to move up and down with the frost, break, and in some case to
eventually "pop out of the ground". A slab in Michigan requires a 36" (it
might be 24" or so - it's been a while) deep "Rat Wall" below final grade.
The "rat wall" is to keep the moles, rats and skunks from burrowing under it
and causing problems for your floor. My pole barn (24' x 40' 2 Story) has
the 42" deep footings for the poles and the 36" rat wall. The 5" to 6" floor
is in 4 quadrants with welded wire mesh and is poured over a 2 foot tamped
sand base. There are three centerline poles to support the second floor. I
originally planned to do automotive work in it, but have since turned to
building a few small boats. Today I would put in a 3" floor with wire mesh
or a wood floor.
I bought a one person gas powered auger and bored 48" to 50" deep 8" dia.
holes below final grade and put in concrete to make the top of the footing
at the 42". The 4" x 6" poles went in after that hardened, dirt was tamped
around the poles so that the bottom of the poles didn't move around and they
were stablized with framing, The rat wall and floor were poured on top of
tamped sand as a single pour. That fills in around the poles and everything
is solid. My wife and I built all of the barn (with some help from friends)
except the concrete floor work that we had professionaly done.
The only problem I have is because the service door is next to one of the
poles and the floor moves up slightly in the winter due to frost causing the
door to jam. I may move the door so that both sides are on 2" x 4"s
supported from the floor and that should solve the problem.
If I were building the "same" barn today, I would pour an exterior wall
foundation (48" deep x 16 or 18" wide) with interior pilings and install a
suspended wood beam floor on the pilings. The whole barn would be stick
built rather than a pole barn. It would have been a lot easier than dealing
with the poles when they started to twist as the whole structure aged. It's
about 8 years old now. In my area it is almost impossible to get 4 x 6
poles that are not twisted. The wood floor would have turned out to be
about the same cost as the concrete floor over sand and it would better suit
my needs today for nailing braces for boat forms. It would also be a heck
of a lot easier on the feet.
Just my thoughts and how I did it. Good luck with it.
John
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