A better workshop foundation?

[Bill Jobe]

Had a guy all set up to make a compacted gravel base for my new 12x20 Amish shed. Then I had 2 more guys show up to bid on the job. Both told me they thought compacted gravel was a bad idea, even with an 8x8 treated frame made in 3 sections with common sides. Some settling was inevitable they both believed. The first guy was just starting to tell me of a better way using sonotubes and pouring concrete "pads" down 30" and leveled perfectly with on another when a second guy showed up and agreed that he thought that would be far more stable. The first guy said he thought just one in each corner for the skids to sit on would suffice.
I did not care for his suggestion and he soon left as I was discussing with the 2nd guy what he proposed. It was his opinion that 4 along each outer skid and 2 more under separate skids near the center of the building.
I'm convinced now his plan is the way to go and I'd like to get some opinions from members here on that method.
He told me the cost would probably be fairly close to a framed compacted gravel pad, or perhaps a bit less.
Please share your thoughts on this idea.
Also, all the while thinking sound deadening it occurred to me that a hard rubber pad on top of these structures might help isolate sound transmission. Any thoughts on this idea?
The shop will have 4x6 skids notched 1" for each 2x4 joist placed 12" on center and a 3/4" plywood floor.

[Reed Gray]

I did concrete work for 30 years. Gravel will settle. How much depends as much on how it is put in as it does on the type of graveland the base you put it on. Mostly there are a lot of voids in gravel, and the weight of it and what ever goes on top of it will push it down into the dirt and/or sub grade. They do use a fabric type of mesh under some roads now which kind of acts like a big snow shoe. That helps some. You can put a lot of fines (sand and/or dirt) on top and wash that down with a lot of water and it makes it more solid, but even gravel roads get ruts in them from constant use. By the time you do the sono tube route, you may as well go ahead and pour a 4 inch slab. The slab, again, works like a big snow shoe. You may do okay with a smaller slab, but having concrete to sit the shop on is the most solid way to go. Plywood will flex. As far as sound deadening, not much noise from turning wood...
robo hippy

[Bill Jobe]

I did concrete work for 30 years. Gravel will settle. How much depends as much on how it is put in as it does on the type of graveland the base you put it on. Mostly there are a lot of voids in gravel, and the weight of it and what ever goes on top of it will push it down into the dirt and/or sub grade. They do use a fabric type of mesh under some roads now which kind of acts like a big snow shoe. That helps some. You can put a lot of fines (sand and/or dirt) on top and wash that down with a lot of water and it makes it more solid, but even gravel roads get ruts in them from constant use. By the time you do the sono tube route, you may as well go ahead and pour a 4 inch slab. The slab, again, works like a big snow shoe. You may do okay with a smaller slab, but having concrete to sit the shop on is the most solid way to go. Plywood will flex. As far as sound deadening, not much noise from turning wood...
robo hippy

There will be with a 5hp DC.

[Reed Gray]

A 5 hp DC in a 12 by 20 shed??? That size of DC would do fine in a 2000+ sq. ft. shop, maybe even bigger if it is a good system. Lathe on concrete slab. The DC, depending on what type and style (2 stage?) would do okay on some of the 12 X 12 inch pavers, but I would want it anchored to the walls some how. Most of the noise from a DC is from the impellor blades and air flowing through the pipes, not from machine vibration.
robo hippy

[Bill Jobe]

With the shed on a slab wouldn't the noise from just the impellor increase? Wouldn't every noise inside the shed be louder outside with the shop on a slab?

[David L Morse]

With the shed on a slab wouldn't the noise from just the impellor increase? Wouldn't every noise inside the shed be louder outside with the shop on a slab?

The plywood floor will transmit much more sound than concrete. Imagine a piano with a concrete soundboard or an acoustic guitar with a cast concrete body. Coupling sound vibrations to air takes a lot of motion and plywood will flex more easily than concrete.

[Jim Becker]

Pouring a slab may have local zoning implications...check on that before deciding between a slab or the concrete supports. A slab would be "more permanent" than posts. From a cost perspective, the concrete posts "may" be less expensive and you can still put in geo-textile covered with compacted stone to keep things clean under the shed if you want.

[Bill Jobe]

So how many sonotube piers do you think would suffice?
One bidder said 1 in each corner would work what with the 12" on center 2x4 joists. Another recommended 4 on each outer skid and one under each of the 2 inner skids near the center of the 20' span.
I called the Amish builder and he strongly suggested 4 under each outer skid (there are 4 skids) and 3 under the inner most 2 skids.
Just called the guy wanting to use just one sonotube,in each corner. I had called him because after more than a week I was wondering why I had not received his bid. He told me he was waiting on me to make up my mind.
The contractor suggesting 4 on the outer skids,plus 2 more in the middle of the 2 center skids has not gotten back to me either.

Would members here please give me their honest opinions as to making a foundation using sonotubes.
They have not started building my shed yet though I ordered it nearly 5 weeks ago.
I am having a lot of trouble understanding the vast differences between bidders and I'm about to the point of doing the sonotubes myself.
Need advise, please. Bill


The shed will be used to store 2 600lb motorcycles, a Grizzly g0766 lathe, more than likely more woodworking machines in the future such as a good band saw. Also will be using for the rest of my tools, miter saw, heavy bench and vice, small table saw and storage for many other things. May also move my reload bench to the shed which weighs about 250lb with press.
If I go with slab I'll have to deal with additional codes. But I've not ruled that out. I will also be storing sveral hundred pounds of kiln dried wood.

[Reed Gray]

If you go the sono tube route, for a 12 by 20 foot shop, then minimum one in each corner, one in the middle of the 12 foot side, and 2 in between the corners on the 20 foot side. They would need to be pretty much dead level with each other. Easier to pour a strip footing, maybe 12 inches wide, and 6 inches deep. You could get away with a full 4 inches deep. Rebar, one piece minimum around the perimeter. 2 pieces is better. It does spread the load, and keeps it together when it cracks. Only 2 guarantees you can give about concrete is that one it will crack, and two, no one is going to steal it... Look into the cost of a full slab, 2 by 6 outside frame box, slab about 4 inches thick. Rebar 2 ft. on center, not mesh (it always seems to be on top of the slab when you are finishing it, or down in the gravel. With sono tubes, you can get a bunch of bags of fence post mix, and it will work, but it is a lot of work to do. If you get one of the portable mixes on site dispatch trucks, if they can get back to it, best value is a strip footing or a slab. Some even have chutes that will swing back and forth to place the concrete on the ground. Don't try to pour it yourself unless you know concrete or it will work you half way to death, and you are stuck with the final product. From what you are going to put into the shed, it sounds like it is about half the size you will need unless every thing is moveable, and every time you want to go work in the shop you have to move a bunch of stuff out of the way. Out where I am, you can do 200 sq. ft. without having to get a permit. No idea what code is where you are. Some times a car port can be done with slab and no permit. They may require one side to be open and the other 3 can be enclosed. I am limited on my lot to any out building having a maximum size of 10% of the total surface area of the lot. I had to cheat and put in a small 'living area' in the shop. I may rent or use it for office space. Hope this helps some....
robo hippy

[Bill Jobe]

Well since it's been 5 weeks since I put down the downpayment i'm sure I could make it longer, but I cannot go beyond 12' wide and still get it to the back yard.
This whole thing has been very stressful and i'm almost to the point of putting in sonotubes myself.

[David Utterback]

A good source for information may be your local permit office. They can let you know how deep to place the sonotubes to avoid heaving from frozen soil, if that is likely to happen in your area. They may also help with load bearing calculations to address the number needed and locations.

[John K Jordan]

Well since it's been 5 weeks since I put down the downpayment i'm sure I could make it longer, but I cannot go beyond 12' wide and still get it to the back yard.
This whole thing has been very stressful and i'm almost to the point of putting in sonotubes myself.

I forgot what you said earlier, but if possible I would consider giving up on the portable building, pour a slab, and build a building from scratch. You won't be restricted by the access clearance and can make it wider. And building a shop is great fun! When I built my first building (20x20, for a shop) I bought some books to learn how.

Pouring a slab is not all that expensive if you do the forming and prep (rebar, etc.) yourself and pay someone to pour and finish. I've done several buildings here, the shop 24x62 and a recent one for a peacock house 12x24. It took me less than a day to prepare the peacock house slab for concrete.

If the site is not level, you can put in concrete piers and build your own wood-floored building, either on posts or as a portable building - exactly as the Amish building you've ordered. (Go to any place that sells these and look underneath and see how simple they are made.) BTW, if using piers to support a wooden floor building for heavy shop equipment I would put piers in the middle as well as around the perimeter to better take the weight - but a slab would be far better. If you know where the equipment will be placed you can even position piers appropriately at the expense of future flexibility.

Building a small structure on a slab is easy if you have mobility, can design and measure, and are handy with tools - and most people who play with wood can handle the tools. I've built a number of buildings, sheds, and decks here and at other places where we lived. There is also a tremendous satisfaction in building and working in a shop you built yourself! It is usually easy to find someone to help with things like trusses and setting large poles. I've developed ways to do most of it by myself using big C-clamps and braces, even when building with timbers so heavy I had to drag them to move them.

Alternatively, there are many people who will come in and put up a small building for you. If the site is prepped the cost may be less than you think and it can go up quickly (a day or two, depending on the design). Several times I've hired a builder friend from our church to build farm buildings and extensions or to help put up a roof - he brings a helper and they are very quick. He is willing to do small jobs like this by the hour instead of by the job which can save a lot of money since a contractor will often double or triple a job estimate to protect himself.

JKJ

[Ric Flanders]

Personally I would go the sonotube route as your contractor suggested. Its the strongest and most cost effective way to go. Having a wood floor is the most comfortable in the long run, but mass does a lot to dampen noise so if sound is a higher priority than cost and/or comfort get a concrete slab. If you do an all wood floor, add another layer of 3/4" plywood with a layer of hardwood floor underlayment (dense roll foam) between the two plywood layers. This added layer adds mass and rigidity. The foam isolates vibrations and also acts as a vapor barrier from the ground. Your back, knees and tools will appreciate this option in the long run!

[Bill Jobe]

The weight will be spread more evenly with an Amish building. The weight will be on 4 20 foot long 4xs.

I recall quite a number of years ago when Billy Myers built a new drag strip in Texas. It's been said it was pre-stressed concrete, something that meant a lot when you are trying to apply 10,000 hp and get it to stick.
If memory serves that is where the first 300mph run was made.
Not official according to NHRA, but 300 just the same. Eddy Hill, I believe.
Could that maybe be what Frank was referring to?

[Andrew Seemann]

If you went the slab route, you probably would not need to go all 32 inches down to the frost line. Here in MN, for detached buildings like garages and sheds, we normally use a what is called a floating slab foundation. 4 inches thick in the middle and the outside is 12" x 12" tapered up to the 4" middle. The increased thickness on the perimeter is to support the weight of the walls. Any internal support posts would also require a thickening of the slab under them. The main reason for them here is that they work, and we don't need to go down 42 - 60 inches to get below the frost line for a simple outbuilding. Main thing is that you can't have a direct connection to a building with frost footings (like a house), because they may move at different rates in the spring thaw.

http://www.minneapolismn.gov/www/gro...ert_264724.pdf