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Shed Foundation Help

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http://boards.diynetwork.com/eve/forums/a/tpc/f/9321916776/m/5533932177

Jun 11, 2013, 01:05 PM
kal72
Shed Foundation Help
I want to build a platform for a pre-fab 6x8 shed in my backyard/woods,just to hold the winter tires, lawnmower, etc.

The plan is to level the base site and build a 2x6 or 2x8 and plywood platform supported at the corners and middle by concrete blocks (either solid cinder blocks or those blocks that accept a 4x4 post).

The terrain is very rocky with rocks varying from fist size, to shoebox size, up to 400 lbs rocks that I have had to pry out of the ground. The frostline here in Nova Scotia is 36" and if i could dig, I'd probably use concrete in sonotubes to support my base. Problem is, there is no way I can dig to that depth. My questions:

1. For a utility shed, am i really concerned with heaving...can my shed be a "floating" shed and be shimmed in the future if it becomes noticable?

2. Is there any value in pouring some concrete (maybe 6-10") into whatever depth and shaped hole I manage to dig between the rocks as a base for my blocks or will that just crack and fail? How would I form the concrete in this approach?

3. Would it be better if I try to dig down maybe 12" below grade fill with clear gravel and then compacted crushed gravel up to level and then set my blocks to that.

4. In either approach (2) or (3) due to a sloping site, I assume I can can just use a second, third block on my low side set on whatever base (concrete or gravel)

5. If I go with the concrete option, is there any value in using a short sonotube that comes above grade? I.e. if I was able to get the sonotube 12" below grade could I have it extend 12" above grade, or is that a tipping hazard?

This message has been edited. Last edited by: kal72,

Photo of site prep

Jun 11, 2013, 02:31 PM
Sparky617
Since it won't be attached to the house, I'd probably go floating.


General Disclaimer

Any advice given here is general in nature and is not necessarily valid for your given area. If in doubt check with your local codes enforcement department for what is required when doing electrical, plumbing or structural work on your house. Permits may or may not be required in your area and home owners may not be able to DIY some tasks. I have no way of knowing if you have the skills needed to complete the tasks you are asking about, when in doubt seek professional assistance.

My advice may be worth exactly what you pay me for it. :-) For the record I did not stay in a Holiday Inn Express last night.
Jun 11, 2013, 07:08 PM
redoverfarm
If it were mine I would also make it floating. Layer of gravel and blocks(leveled). The actual amount that will rise in freeze will be very little and should settle back when Sring arrives. Since you do not have any drywall then it will not be noticed. If you are building a platform and setting a building atop then make sure that it is properly flashed so water will not enter between the platform and the building.

Most "pre-fab" are constructed on some type of foundation. Just wondering why you are going to build an additional foundation? Can you not just level and block up at the corners and midpoint on the sides and ends?

This message has been edited. Last edited by: redoverfarm,
Jun 11, 2013, 07:23 PM
Jaybee
Yup, another vote to make it floating. Use whatever method makes sense to get a level building surface - gravel will probably work the best but the block idea will too.

Consider if you have any windage - you may want to install some form of tie-downs.


Jaybee
Jun 11, 2013, 07:57 PM
kal72
Thanks for the responses.

I am building the platform/foundation because I thought the shed kit just came with a floor. I know those resin sheds need a separate platform, I thought the wooden ones would as well. If the wooden shed kit has a floor/platform that can be installed directly on top of the blocks (4 corners and midpoints)that saves me some work and expense on a separate platform.

I will look into tie down options, as you suggest Jaybee.
Jun 11, 2013, 09:07 PM
kal72
In the end, I might build one from a plan instead of a kit. So I have to be prepared to build a separate platform/base if i go that way
Jun 11, 2013, 10:55 PM
SturdyNail
As Jaybee noted, you may want to install tie-downs.
In my area, building a shed requires a permit.
One of the requirements is for the shed to be anchored, via a heavy gauge chain, to concrete set below the frost line.
You may want to check your local codes.
Jun 12, 2013, 05:41 PM
Sparky617
In my area I can build a shed up to 10x12 or so without a permit. Provided it doesn't have any electric.


General Disclaimer

Any advice given here is general in nature and is not necessarily valid for your given area. If in doubt check with your local codes enforcement department for what is required when doing electrical, plumbing or structural work on your house. Permits may or may not be required in your area and home owners may not be able to DIY some tasks. I have no way of knowing if you have the skills needed to complete the tasks you are asking about, when in doubt seek professional assistance.

My advice may be worth exactly what you pay me for it. :-) For the record I did not stay in a Holiday Inn Express last night.
Jun 15, 2013, 06:38 AM
kal72
I have my site measured and string levelled so i can see where things line up. I think i will go with three 4x4" skids to support 2x6 floor joists. due to the slope, one side will be about 24" above grade - the skid on that side will just clear and span a large rock outcropping but will need to have raised support in each corner. What is the best way to build up? Is it enough to stack six 4" thick 8"x16" solid blocks on 6" of compacted gravel? I could get 8" thick block for fewer to stack but they would be hollow. Do I need to worry about the stability of that stacked block pier, could frost heave take a block out of alignment?
Jun 15, 2013, 08:15 AM
Sparky617
By skids do you mean shipping pallets? Those will not make a good long term foundation. They generally aren't pressure treated and even if they were they aren't designed for long term wet ground contact.


General Disclaimer

Any advice given here is general in nature and is not necessarily valid for your given area. If in doubt check with your local codes enforcement department for what is required when doing electrical, plumbing or structural work on your house. Permits may or may not be required in your area and home owners may not be able to DIY some tasks. I have no way of knowing if you have the skills needed to complete the tasks you are asking about, when in doubt seek professional assistance.

My advice may be worth exactly what you pay me for it. :-) For the record I did not stay in a Holiday Inn Express last night.
Jun 15, 2013, 08:21 AM
kal72
4x4 pt posts one allong each side, one down the middle, sitting on gravel and 1-6 blocks