New Shop Foundation

I am in the beginning stages of planning a 32x48 detached shop on my property. I was originally going to set 2' x 2' x 4'8" piers and frame a 2x12 PT floor system on top of those. I just received a quote to set and backfill approximately 15 of these piers and the price was $10,000. There is grade change from front to back, but I plan to build up off the piers with 8x8 PT so I have a level floor. This was about 3 times higher than I had anticipated so now I am looking at other options.

I want to have a wood floor with some accessible space beneath to run my DC. Code requires that if I use piers they must be frost protected.

Do I use sonotubes or another kind of footing tube? Find a more level location and re-price the piers vs. a slab? I don't mind putting in some manual labor to cut down on the costs, just want to look into alternatives without compromising the strength of the foundation.

Any thoughts on this would be appreciated. Thanks in advance!

Have you looked at putting a stem wall around the perimeter? How deep is your frost line? I could see piers down the center, or maybe you would want 2 rows of piers to shorten your span. Personally, I would look at setting it up and pouring it myself. My experience is that the footing is the hardest part. Pouring that is. You need some help to pour footings, but stem walls are easier. Just back a truck up to the corner and thin the mud so it flows down the wall.

I need to be a minimum of 3 feet to get below the frost line. Is a stem wall the same as a frost wall? How would you recommend constructing the forms?

Jim - You are right about pouring the footing. They are not much fun. And yes the walls are easier to pour but if you add enough water to make the concrete run down the wall, your concrete won't be worth a damn. You shouldn't use anything less than a 3000 pound concrete and a 4" slump. If you make it too thin, it weakens the concrete.
Josh - Can you and have you thought about pole barn construction? Where I live they require to be down three feet for the frost line but with pole barn construction here, I can pour slab on grade. The posts had to be ground 4 feet and back filled with concrete. Pole barns are much simpler to build and you could probably do a lot of the work yourself. Good luck with your building.

You might price putting in a pier footing and then a block pier using 12" block with rebar doweled into the ftg and filled with concrete. It should be cheaper than a formed concrete pier. I would think you would want a solid block wall for the foundation helping to eliminate the cold and freezing temps from below the floor.

If your local codes permit it, them use an all weather wood foundation (look it up.) It's basically a pad of gravel, instead of poured concrete. There is a drain in the gravel to to take care of any water. This should be "day lighted." Then you lay a sole plate on top. You build walls out of 2 X 6, and 3/4 plywood, all of which has been treated for below ground use. All fasteners have to be stainless steel. It forms both footing and stem wall. The first I saw is my neighbor's house which is approx 25 years old now. In 1994, when we were in Alaska, they were going wide open building using this system. Helped a friend do one in SC in the early ninties.

Thanks for all the input guys, lots of great ideas, guess I have some more homework to do now. Hopefully I'll have photos to post in the near future.

I would recommend you look at a crawl space. It gives you access below the floor and also allows you to have a wooden floor. Like Bruce mentioned, poor a footer. When I was building HFH houses our footers were 8" high and 16" wide, after that we then blocked up to our desired height. I wouldn't go any shallower than 4'. I am looking at building my shop on a 5' crawll using foam forms. for a crawl you will also need at least 1 beam and depending on how much heavy cast iron you have you may need 2......

Bryan

A 4' tall stem wall on top of a 8" footing will give you 56", so 3' below ground leaves you 20" above the ground. If that is too tall, you can bury a little more of the stem wall or put a piece of quarter round in the form to stop the top of the concrete. Concrete will flow down a wall if it is thinned a little, doesn't have to be like water. The concrete put in with pump trucks is thinned more than you have to thin to get it to flow down a wall. Gates hardware works great with BB form plywood. You can lay 4 x 8 sheets down and use gates ties with 5/8" rods on both sides of the forms, have to use hinges on the corners so they hold. And a 2x4 top and bottom of the plywood. To hold the outside of the form in place, and top from spreading. You can reuse the plywood in the building. Spray with form release oil and the forms come off the concrete pretty clean.