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Old 11-14-2012, 03:59 PM   #1
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Building a shed on a Slope


Plan is to build a 16x16' floating slab in the backyard. Unfortunately, I had this grand idea without measuring anything that the slope wasn't a huge deal and the retaining wall wouldn't be too tall. After digging and leveling the subgrade, the retaining wall would be about 4' tall.
The slab will have turn down footings 12"x12"x12" around the perimeter with 4" thick in the middle.
Having only poured and finished concrete for our driveway with my dad back when I was 12 yrs old, I have little to no recollection of how the process went.

Here's how I have figured out the process:
Dig so the shallow end will be 1' deep,
Slope the subgrade 1/4" per ft.,
Pour mixed gravel(what sizes?) to create 4" thick compacted base,
form up and level forms 2" above grade,
use slab on two sides as retaining wall bases,
leave 1' between retaining wall and shed.


Questions -
Should I dig deeper than 1' on the shallow end? Can I put some of the excavated soil/sand on the shallow end to raise and re-grade(proper term?) and minimize the retaining wall height?

When I pour my gravel base, how do I get around the turn down footing issue? I don't think the gravel would stay put in the same profile/cross section of the turn down footing. By that, I mean will I be able to have the perimeter gravel slope down 8"? How is this accomplished?

Is it ok to have the slab 2" above grade? should it be a different height? Does it matter? The more above grade I can get, the shorter the retaining wall can be.

Would you leave more space between the retaining wall and the building? if so, how much? enough to fit 2 body widths for maintenance? Would you use the slab as a retaining wall base?



Btw, I'm in Minnesota, the freeze is coming so I plan to pour this weekend. I have heaters and blankets ready to go, just need to figure this out.
I think that's all for now. Thanks all!


This is my thinking for the cross section of the slab, minus rebar and mesh. Is this right? or do I leave an extra 8" of subgrade/soil in the center and compact gravel on top of that and taper it down to the footing?



Last edited by skhots; 11-16-2012 at 10:00 AM.
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Old 11-14-2012, 04:31 PM   #2
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Building a shed on a Slope


depth depends on if you're planning on installing your footing below the frost depth for your area. were you required to file a permit, if so then you'd have to find out what the required frost depth is.

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Old 11-14-2012, 04:36 PM   #3
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Building a shed on a Slope


Yes, i filed for a permit, was approved based on what I've told you guys. 1' deep on the shallow end, 12"x12"12" footings, etc..
I assumed they didn't ask questions or require me to go below the frost line because it's just for a one story accessory structure?
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Old 11-15-2012, 08:25 AM   #4
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Building a shed on a Slope


be sure and build your retaining wall strong, just build it like a standard wall at 16" centers with single top and bottom plates and osb plywood with kickbacks every 16" or 32" and at every break/seam in the wall. plan on going more than 2" above grade on the high side and I'm not sure what you mean by ( leave 1' between retaining wall and shed.)

Last edited by hand drive; 11-15-2012 at 08:29 AM.
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Old 11-15-2012, 08:47 AM   #5
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Building a shed on a Slope


Quote:
Originally Posted by skhots View Post
Yes, i filed for a permit, was approved based on what I've told you guys. 1' deep on the shallow end, 12"x12"12" footings, etc..
I assumed they didn't ask questions or require me to go below the frost line because it's just for a one story accessory structure?
the choice whether to go below your frost line I guess then is your decision. it depends on if you are concerned about frost heave or not.

myself I'd use a 3/4" to 1-1/2" mixed crushed stone base. equal size gravel is difficult if not impossible to compact, whereas crushed stone of different sizes tends to lock together.

I take it you dug out the side of the slope so that your footings are at the same elevation?
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Last edited by GBrackins; 11-15-2012 at 08:51 AM.
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Old 11-15-2012, 08:58 AM   #6
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Building a shed on a Slope


Hmm, didn't even think of a wooden retaining wall, was just automatically thinking of concrete blocks. Thanks for that idea. The only problem I see is having to dig further into the slope.
By leaving 1' between the retaining wall and shed, I mean building the shed 1' away from the retaining wall.
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Old 11-15-2012, 09:09 AM   #7
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Originally Posted by GBrackins View Post

I take it you dug out the side of the slope so that your footings are at the same elevation?
The side of the slope...? Say the slope rolls from north to south, side of the slope would be the east/west walls? If so, yes, right now the whole floor of the excavation is at the same elevation. I'm not entirely sure how I'd compact the interior 14' SQ gravel to be 8" high.
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Old 11-15-2012, 09:47 AM   #8
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Building a shed on a Slope


Quote:
Originally Posted by skhots View Post
Hmm, didn't even think of a wooden retaining wall, was just automatically thinking of concrete blocks. Thanks for that idea. The only problem I see is having to dig further into the slope.
By leaving 1' between the retaining wall and shed, I mean building the shed 1' away from the retaining wall.
if you plan to extend the concrete past the walls of the building then inset the bottom plate into the slab so that the water will not wick under the wall. it is best to have the edges of the wall to the edge of the concrete and have the siding lap the concrete...

Quote:
Originally Posted by skhots View Post
The side of the slope...? Say the slope rolls from north to south, side of the slope would be the east/west walls? If so, yes, right now the whole floor of the excavation is at the same elevation. I'm not entirely sure how I'd compact the interior 14' SQ gravel to be 8" high.
crush and run can be tapered to go to the footings along the sides of the structure. 4" below top of concrete in the middle and tapered to your footing size along the sides...
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Old 11-15-2012, 09:54 AM   #9
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Building a shed on a Slope


Didn't think of the water wicking under the wood. I guess gravel would just be between the slab and retaining wall? with the gravel level below the slab?

I understand tapering the gravel to the footing but I just imagine pouring the concrete and having it drag some gravel down to the footing as I shovel the concrete around.

Thanks again for the input.
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Old 11-16-2012, 10:01 AM   #10
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Building a shed on a Slope


added picture for clarification, would like to get a definite answer before I order 5 yards of gravel. Thanks....
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Old 11-16-2012, 10:35 AM   #11
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Building a shed on a Slope


Quote:
Originally Posted by skhots View Post
Plan is to build a 16x16' floating slab in the backyard. Unfortunately, I had this grand idea without measuring anything that the slope wasn't a huge deal and the retaining wall wouldn't be too tall. After digging and leveling the subgrade, the retaining wall would be about 4' tall.
The slab will have turn down footings 12"x12"x12" around the perimeter with 4" thick in the middle.
Having only poured and finished concrete for our driveway with my dad back when I was 12 yrs old, I have little to no recollection of how the process went.

Here's how I have figured out the process:
Dig so the shallow end will be 1' deep,
Slope the subgrade 1/4" per ft.,
Pour mixed gravel(what sizes?) to create 4" thick compacted base,
form up and level forms 2" above grade,
use slab on two sides as retaining wall bases,
leave 1' between retaining wall and shed.


Questions -
Should I dig deeper than 1' on the shallow end? Can I put some of the excavated soil/sand on the shallow end to raise and re-grade(proper term?) and minimize the retaining wall height?

When I pour my gravel base, how do I get around the turn down footing issue? I don't think the gravel would stay put in the same profile/cross section of the turn down footing. By that, I mean will I be able to have the perimeter gravel slope down 8"? How is this accomplished?

Is it ok to have the slab 2" above grade? should it be a different height? Does it matter? The more above grade I can get, the shorter the retaining wall can be.

Would you leave more space between the retaining wall and the building? if so, how much? enough to fit 2 body widths for maintenance? Would you use the slab as a retaining wall base?



Btw, I'm in Minnesota, the freeze is coming so I plan to pour this weekend. I have heaters and blankets ready to go, just need to figure this out.
I think that's all for now. Thanks all!


This is my thinking for the cross section of the slab, minus rebar and mesh. Is this right? or do I leave an extra 8" of subgrade/soil in the center and compact gravel on top of that and taper it down to the footing?

from the pic it looks like it could be a pool of water there at all times. it needs a foundation drain and then possibly a yard drain to get it away from the structure....
edit.. "shed on slope" is the thread title so just water coming from the high side of the structure will be the issue maybe

Last edited by hand drive; 11-16-2012 at 10:39 AM.
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Old 11-16-2012, 10:42 AM   #12
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Building a shed on a Slope


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Originally Posted by hand drive View Post
from the pic it looks like it could be a pool of water there at all times. it needs a foundation drain and then possibly a yard drain to get it away from the structure....
edit.. "shed on slope" is the thread title so just water coming from the high side of the structure will be the issue maybe
Why do you think there'd be a pool of water there at all times? Isn't that the point of sloping the subbase and subgrade? To direct water away from the shed?
In case it wasn't obvious, I just forgot to add soil back over the exposed gravel on the sides of the slab.

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