building on a slope

[james53546]

I am looking at building a 24x24 garage on a slope. What would the greatest slope to put a slab onto. I know i would have to bring it up to grade. where I am looking to build its about a 3 ft drop. Or would it be better to put a foundation under it. or move it to more of a level area. If I have to move to a better location what would the most of a slope can i have. I would like to do a floating slab to be a little cheaper. has anyone done this before? any help would be great, by the way i'm from southern Wisconsin.

jim

 

[firecracker]

The only way to go with that bud is with stepped foundations.

 

[timewarp]

Better to cut it down on the high side if possible then you don't have to worry about compaction of fill. Or cut 1/2 the depth and use the removed material to fill the low side. You can build on much steeper grades than 3' in 24'
Also you could build into the hill and have a concrete wall on the back side with dirt up to it.

 

[kbs2244]

I am assuming the slope is away from the opening side?
Downhill to the back?
If so, IMHO, the best thing to do is to take your time.

Build a retaining wall at least 3 feet beyond your back wall.
Fill in the void.
Wait a winter for the fill to settle.
(You can park on it in the meantime.)
You might be surprised at how much it settles.

Then pour your slab.
You will still need pea gravel, etc under the slab, but
the well settled fill will support the slab enough to prevent cracking.

You can do it faster with watering and compacting during the fill dumping.
But it adds cost and time.

 

[james53546]

I forgot to say that the front of the garage would be on the high side. If I change were i was to put the garage, what would the most That I would want to fill to level off? If I have to put a foundation under it I will but I would rather not. Thanks for the input. What would be the best to use for fill? The best for compaction.

 

[Gary S]

My garage sits on a slope. I dug the high side low enough to get fill for the low side. Then I put in a retaining wall on the high side to hold the hill and a trench about 3 feet wide that drains across the slope.
That allowed me to pour a floating slab and not have water problems.

 

[james53546]

Does a stepped foundation have to go below the frost line? I'm not to familiar stepped foundation.

 

[james53546]

the biggest thing that I am worried about is settling, and the garage being damaged.

 

[Snap50]

There is really no limit on the grade differential if you properly design the foundation and get a contractor who knows how to compact structural fill, preferably a commercial contractor. The structural fill is not your average soil and you might have to have the appropriate material trucked in. And you are striving for 95% optimum compacted density. All are important issues that you might do well to hire a local Engineer to send you in the correct direction. It's going to be a heartbreak if a shortcut causes distress for your building

On another note, all foundation elements want to be on undisturbed virgin soil; none go on fill otherwise you will get settlement. And of course you need to be below the frost line with all footings.

You might consider putting a layer of 3/8" crushed stone directly beneath the slab. A thicker layer would help spread loads over soft spots.

 

[TheShrine]

The NE front of The Shrine is 12" above grade. The SW back is 5' 6" above grade. It is "floating", on solid rock attached to grade w/ rebar drilled into the rock every 12" on perimeter and too many places to count in the center.

It's a common practice to build "above grade" here in the Hill Country since you can't always get "below grade"! We are on rock...if you are not....then.....

 

[Bondo]

I forgot to say that the front of the garage would be on the high side. If I change were i was to put the garage, what would the most That I would want to fill to level off? If I have to put a foundation under it I will but I would rather not. Thanks for the input. What would be the best to use for fill? The best for compaction.

Ayuh,.... So long as ya fill the area level for the floatin' slab,...

The areas around the slab can drop at a 1'x1' foot slope, no other foundation is needed....

Crushed Gravel compacted in 6" lifts is no doubt the Best fill...
How deep you can fill is however much fill ya wanta buy...

 

[james53546]

Thanks for all the information

 

[Engineer61]

You need to make up more than that 3 feet of slope, to keep water from flowing down your hill into your garage through the doors you'll need to raise that floor to put an uphill slope on your driveway. Else you'll start to understand what the phrase "a river runs through it" can really mean.

 

[james53546]

This garage will be going into my back yard.

 

[james53546]

From the front to the rear there is a 3 ft drop. thats in a 24 ft run.

 

[retrobuilder]

Not that steep, likely two steps about 18" high, 3 max at 12" footing- below frost line.- Is it formed or masonry wall? Your local concrete company may have advise for you locally or search a concrete industry site? Your drive way garage door slope needs to be considered for drainage.