Getting ready to build a freestanding shop building in my backyard, this spring. Everyone recommends going with a conventional wood framed floor for comfort (easier on the legs and joints). With that in mind, I’m thinking of going with a crawl space. Conventional wisdom in SE Michigan is to use an 8″ wide by 42″ deep trench footing filled with concrete and no reinforcement mesh or rebar. This footing then gets three row of block to create the code required 24″ height clearance in the crawl space. BTW I have heavy clay soil, high water table, and a 42″ frost depth.
Does this setup sound like a reasonable way to go? Do I need some type of mechanical attachment from the footing to the sill plate? Or will foundation bolts grouted into the top row of block do the trick? Any ideas, alternatives or suggestions are much appreciated!
Replies
If your frost depth is 42" then 42" for the foundation depth is too shallow. In a cold winter or one with low snow your foundation will heave. Clay soil and bad drainage make it much more prone to heaving.
You definitely need to fasten the structure down. The main reasons are wind and earthquakes. While an earthquake is rare in your area, it's not completely unheard of. If the building is not fastened down then even a relatively mild shaking can shift the building off the foundation causing expensive damage. And, very strong winds can shake a building pretty good, too.
If you are going to put three courses of block on a poured base, I'd recommend vertical rebar every 4' or so, sticking up 22" from the base, and grouting the cores of the block that contain the rebar. Install anchor bolts in the grout when it's placed.
if you going to back a truck into the shop then wood will not work.
sure it would...
build to fit the need...
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Martrg ,
Where you are 42" is not enough . Go 50" , use rebar . Bolt sill to foundation . If you use 3 courses of block , grout solid . Then go .
Whoa!
You don't use rebar in your footing? I suggest using a rebar mat in the ftg. and tie verticals for the grouted block. Do go a little deeper to account for the colder winters to make sure. Also don't forget a french drain around the ftg. to try and move the ground water away.About tying the block to framing......Definitely, besides earth tremors, wind and tsunami's,
(how close are you to the great lakes) What about driving into the corner of the shop with your truck? Or the new teen age driver down the road? Many years of planing hardwood with a not so tuned planer? All of the above create side movement/vibration in a building.
So put a good anchor bolt in every grouted block- at least every 4 ft. oc and two in the corners where the sill plate joins.
If your going to use rebar in a footing , it's always a mat . Everything else has already been stated. Read twice and think once .--WOAAAAA.
I'd do it the easy way!
Have someone come in and dig the trench deep enough to get under the frost and then put in ICF's
(insulated concrete forms) those are the syrofoam "building blocks" that go together like a giant set of leggos' . they take practically zero effort to set up and pour into and aren't terribly expensive..
If you are really clever you can set your ICF's up over a footing trench and add the self leveling agent after you pour the footings in and they take a little set!
That sounds cheap and easy and potentially workable if that is the typical way it is done there, but for most places, it can create a lot of probelms.
First - the footers. A trench filled footing/grade beam with rough edges like that will give the frost a good grip on it to heaver it up and out. a formed footer with slick finished sides takes longer but will not afford the frozen soil a chance to grab at it.
We form the footer 24" wide by 8" deep at 48" down under, then lay the block on up. That means a wider excavation and labor time laying block, but a better job.
we also never pour any crete without steel. that sounds plain rediculous.
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Unreinforced concrete is just an expensive way to lay a rubble foundation.
rubbkle is fine on a solid base, but he said that this was on/in clay. That pretty well gaurantees cracks in th eblock wall,IMO
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I agree. I wasn't endorsing rubble foundations, just observing that if you want one it makes more sense to make it out of rubble than spend a lot of money to pour concrete and then wait for it to break up.
Uncle Dunc,
personally I use rebar as a matter of course, however, I've seen people use concrete block walls withour any rebar in it and the building inspector is happy. To me a block wall is designed to fail and yet tens of thousands of homes are built that way.. Over a block wall I'll take unrebarred poured wall any day!
I plan to add to my shop in the next couple of years. I will probably have a raised floor like you framed with wood, but will perch it on piers for the economical method. Don't know if that is doable in your codes area or not...
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I'm in MI also (south central)
They stopped allowing trench footings some years ago in my area (just South of Lansing).
42" minimum to bottom of footing is the requirement, but 36" from top of a non-formed (ie hand dug trench) to grade is as high as we are allowed to pour a rough faced wall/footing.
16" is the minimum width at the bottom of the footing.
As I understand it, this is a state wide requirement. The only exception is an agriculture building.
Terry
If you are going to pour the footing, why would you then lay 3 courses of block on top of it? Why not pour footing and walls together? Another thing, an inverted "T" type footing is far more stable than the 8" trench footing you describe - gives far more footprint, resists tipping and uplift better and a right angle is far stronger than either of the legs that form it.
And I agree with the others about rebar. It's cheap and easy to install. No way I'd invest however many thousands of dollars in a building and save the couple hundred (maybe) by not putting in steel. Same with slabs - you could probably make the case we overdo it with steel in our slabs, but better too much than too little, no question about that. "Penny wise and pound foolish".
TLE
Thanks for the reply! I live near Brighton. I'm baseing my design on some garages I built for myself and friends 10 + years ago. Most people are telling me to just put up a pole barn with a slab floor, but I want to heat it and make it comfortable hence the wood floor. Have you ever heard of a good way to insulate a pole building?
I build a couple of pole buildings each year, but just don't care for them. I think of them as a livestock barn that is being converted.
My own barn is on a concrete block foundation, although it has a slab floor.
Your material costs are very similiar between pole construction and stick built. The differance is the foundation - it is totally on top of the pole barn cost.
The trade off is with a foundation and stick frame, you have more options to do a better job of insulating and finishing the interiior.
Depending on the size you are building, you could use a pole (pier) foundation to support conventionally framed deck and stick frame the walls.
Terry
Why not pour a slab floor with radiant floor heat? First pour perimeter frost walls, then put 1" insulation around the inside perimeter of the foundation and 2 to 4 inches of foam on the stone base and pour a slab. Radiant floor heat is very comfortable, and is very safe for a wood shop, and you won't have to keep cleaning you heat source.
The idea that wood floors are more comfortable than concrete is largely a misconception in my opinion. If you framed a wood floor you are not going to make it so springy that there is any appreciable bounce to it. And you are not going to sink into a wood surface (even someone with high heels) any more than a concrete surface. The key to a comfortable concrete surface is that it be smooth so it doesn't catch your feet and stub your motion, which can jar your joints.
Concrete has the disadvantage that it's harder on dropped tools.
I had a very smooth concrete floor with radiant heat in my shop and loved it. The only disadvantage was that the heat was not instant.