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Old 05-22-2011, 07:04 PM   #1
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Redoing foundation for 10' by 20' shed


I have recently purchased a house with a rather nice finished 20' by 10' garden house. At one time it was a hot-tub house - drywall and wainscoting on the interior, nice big windows, wood stove etc. The structure itself is great, however it is currently supported on two long 4x4s which themselves are supported on some concrete-filled steel posts (they look like the steel posts you would see in a chain-link fence).

It seems stable, the posts are in poured footers in clean sand, but the floor has some waves in it corresponding to where the posts are, and it feels pretty springy as you walk across the floor.

I am having the yard adjacent to this house regraded and leveled, and some trees removed that (incidentally) will permit heavy equipment access to this building. I would like to get this house on a good concrete slab at it's present location. Since it is on posts, it would seem relatively straightforward to get some steel beams under it, sling it out of the way with a crane onto some cribbing, grade and pour the slab, and sling it back into position.

Does anyone have any experience with this sort of thing, and maybe a ballpark $ figure to do this? Plan B would be a tear-down and rebuild, but this is a big structure and that would entail some costs all by itself.

Many thanks!
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Last edited by Thunder Chicken; 05-22-2011 at 07:11 PM. Reason: Added picture
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Old 05-22-2011, 11:38 PM   #2
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Redoing foundation for 10' by 20' shed


You would have to have the crane come out twice, very expensive I think.
You can build a foundation for this thing yourself if that is what you want to do without having to move the building off site.

I actually did an entire foundation for an 1100 sq. ft. by mostly by myself for my parents about 10 years ago. I used 1/2" steel plates, 6x6 x12' timbers, 4x4 for cribbing, and a few 12 ton bottle jacks.

I supported and dug the foundation one side at a time. Hell of a lot of work to be sure but that was when I was younger and doing most of my work alone.
Not sure that this is what you want to do but just letting you know it can be done if you have the skill, knowledge and at the very least, a plan.

Andy.

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Old 05-23-2011, 03:38 PM   #3
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Redoing foundation for 10' by 20' shed


True, I'd have to get a crane in twice, but it sure would make the job easy.

Does anyone have any pointers on the quality of steel piers (concrete filled)? These seem to be in and pretty stable, but I'd like to know now if they have a tendency to rot out. They are galvanized and I don't see any corrosion, but they don't inspire me like concrete.

The waviness is really in the 4 by 4s that are supporting the building. If steel piers are really OK, that may mean just swapping out the 4 by 4 with something stiffer might be all that is required.

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Old 05-23-2011, 09:02 PM   #4
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Redoing foundation for 10' by 20' shed


Just some ideas here:

Last year I jacked up my 12 x 24 potting shed 2 feet and placed it on a new foundation. Granted it isn't as nice as your finished shed, but the sucker is still heavy. I jacked the shed up using two 10 ton bottle jacks one inch at a time keeping the building level all the time. It was a whole lot of crawling and sliding to place the jacks.

For a new foundation I used a 4 inches of crushed rock called DGA then placed 2 railroad ties side by side, and 2 more railroad ties on top of the first two. I built 4 of these railroad tie foundation structures. The building then was lowered and a small amount of leveling was needed to make the building rock solid. I also used 4 mobile home tie downs under the building and attached the building to these tie downs.

I also considered rolling the building out of the way using several telephone poles as rollers. However, the level spot was just a smidgen to short to allow me to roll the building fall enough out of the way.

Good luck and be safe
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Old 05-23-2011, 09:33 PM   #5
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Redoing foundation for 10' by 20' shed


Another consideration is how close the building is to the neighbor's fence (about 2 feet away). Unfortunately this is side of my "bad" neighbor . Paying someone else to do the job, though expensive, puts an insurance pad between me and the neighbor. If I screw up and the fence gets whacked, it's on me.

Maybe I should just drink a few more beers and learn to enjoy the springy floor

Does anybody have any experience (good or bad) with these steel pilings?
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Old 05-24-2011, 12:25 AM   #6
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Redoing foundation for 10' by 20' shed


Maybe you should post some pics of the structure of the floor and supports under the building, that would help to visualize what you have going on under there. I'm sure what you have could be repaired or reinforced to improve the situation. Depends a lot on the number of piers but 4x4's were not really a good choice for the support beams.

We usually end up needing a crane at least a few times every year for ag construction jobs. A crane would probably not be very practical for your job. You could easily spend $500+ each time you have the crane out. The cheapest crane service around here is $125/hour with a 4 hour minimum and travel time matters, because you pay from the time the crane leaves their office until they return. Of course the larger the crane the higher the price per hour.

Don't know about your access, they would want to be fairly close to the building and you wouldn't want them to cross any sidewalks or driveways to get there as they are very heavy. You are already grading so the tremendous ruts that would likely be left could be taken care of. Many folks underestimate how much room it takes to get a crane in place and operate it, a residential backyard is pretty tight quarters. You would need to find the right crane service too, many will expect you to have the necessary rigging and also to safely rig the lift.
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Old 08-09-2011, 01:07 PM   #7
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Redoing foundation for 10' by 20' shed


Here are 2 pictures showing how the shed is currently supported. There are 2 rows of concrete-filled steel posts (2 rows of 4, 8 posts total) along the long axis of the shed, On top of them are 4" by 4" beams, held to the top of the posts by straps. I'm not sure how the straps are fastened to the top of the posts.

The floor framing looks like 2" by 6" across the short width of the shed. The 4" by 4" beams with 5' spans are obviously not stiff enough for this application, there are big sags in the floor. Besides they are dry rotting and cracking, so they have to go.

Is anyone familiar with the strap and post system used here? Any thoughts on what I can use to replace these beams? Deeper beams are obviously needed.
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Old 08-12-2011, 12:05 PM   #8
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Redoing foundation for 10' by 20' shed


Here is a plan sheet from one of my shed plans. It shows a concrete pier built with 8x8x16 blocks. You will most likely find footings under the concrete posts when you remove them which you may be able to re-use.

My dad moved his shed last year and did it by building two rails from 4x6 lumber immediately next to the shed and then jacking the shed up, placing rails under it, putting 2" steel pipes between the new rails and the existing shed rails and then rolling it onto the new rails built next to the shed. He then built a foundation and then rolled the shed back. He used a nylon car towing strap to wrap around the whole shed and a come along to pull the shed on the pipes.

Another option may be to build a new foundation next to the shed and then roll the shed onto it.

I attached a plan for the concrete pier, i got it from http://www.icreatables.com/yard-and-...rage-shed.html

You can also use cardboard tubes and fill them with concrete, i attached a picture of the use of a concrete tube and post base being used on a deck but it will work the same to hold your shed and floor beam. Using a larger concrete tube and post bases that you attach after the concrete hardens helps to set things perfect. Hope this helps.
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Old 08-12-2011, 12:38 PM   #9
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Redoing foundation for 10' by 20' shed


Setup some cribbing and jacks and then use the machine you'll have on site to "drag" the shed. drag in the direction of the existing 4x4's and use them as the skids. Build the new foundation and then "drag" back and jack it down. If you plan the trades right the machine will still be on site and negate having to pay mobilization fees.
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Old 08-12-2011, 11:18 PM   #10
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Redoing foundation for 10' by 20' shed


I can't skid the shed on the 4" by 4"s as my house is just out of frame to the right of the picture. It will have to be jacked up on cribbing.

Are the steel columns kosher? They seem to be doing the job of holding the shed up and seem strong enough. The problem is really the 4" by 4"s being undersized so the floor has big waves in it.

Getting deeper beams in is certainly needed, but the questions are:

1 - can I reinstall new beams on the current steel columns? I am unfamiliar with these types of columns and don't know if they are an accepted practice or something kludged together. They seem to be up to the job if the strapping system can be modified for deeper beams.

2 - The deeper beams would need to be cross-braced in some fashion for stability. In the picture above with the 2" by 8" sistered beams, the deck is attached to a wall so you don't need to worry about the beams falling over on their sides. How can this cross-bracing be done if the current steel columns are used?

Last edited by Thunder Chicken; 08-12-2011 at 11:24 PM.
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Old 08-13-2011, 09:00 AM   #11
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Redoing foundation for 10' by 20' shed


Steel columns are used to hold up floors in basements all the time.
To answer your questions.
-If the columns are strong enough you should be able to install new beams on top of them. The only way to really know is to have a structural engineer look at the columns and run some calcs on it. They usually charge a minimum fee of around $100 for something simple. The engineer will want to know the wall thickness of the pipe.
-You may consider putting in steel I beams on top of the pipes, they will be stronger for the size of beam, stand up to the weather better. And most importantly you can weld them to the top of the pipes which will strengthen the pier to beam connection.
-If you want to use wood beams then you can have a welding shop build you a beam seat with a 6" section of pipe welded to it that will slip over the existing pipe.
-The beams can be stabilized laterally by using a welded beam seat that goes up the side of the beam or, if you use steel beams they will be braced by the weld to the new pipe, or, if you use wood beams you can put several joists running perpendicular between the beams.
-The more critical question is lateral bracing of the steel columns. They need cross bracing to keep the whole building from moving, in both directions. This can be done with cables and turnbuckles or steel pipes running from the top of one column to the bottom of the next column.

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