Shed foundation opinion

[dtbingle]

Moving into my new house this weekend and one of the first projects will be a 10'x12' shed for lawn equipment. I talked to the city and anything 120 sq ft and under does not require a permit, however sent along ratwall requirements. These are the two options:

1. All structures resting on a concrete floor require ratproofing regardless of size.
2. An alternative (not our choice but an alternative) would involve raising a wood floored structure at least 8” above grade so that the area below is completely open on all sides. This typically involves the installation of 4” x 4” treated posts 42” deep; the resulting open nature of the underfloor space will not provide a nesting area for rodents, however, this configuration is not visually appealing.

Setting posts 42" deep seems like a huge pain for a shed, so I'm leaning towards option 1 of a concrete pad.

What the heck satisfies the "ratproofing" requirement for concrete slab? Is this just sealed exterior seams? A 1 ft stemwall? Something else?

Also, I plan to remove grass, compact the existing dirt underneath, and then pour a 4" slab. Should this hold up fine through freeze cycles? I can't see doing a proper footing down 42" for a 10' x 12' garden tool shed....

 

[ptgarcia]

I wouldn't pour a slab them cover it with a wood floor. Seems like a waste of money to me. I would build a wood floor and support it with concrete blocks/spread footings.

 

[garagelogician]

Also, I plan to remove grass, compact the existing dirt underneath, and then pour a 4" slab. Should this hold up fine through freeze cycles? I can't see doing a proper footing down 42" for a 10' x 12' garden tool shed....

I would remove all topsoil/organics, replace with sand or crushed stone, compact it and pour the slab. Make sure you use reinforcing. As for the ratproofing...I know nothing about that.

 

[adam0872]

I would remove all topsoil/organics, replace with sand or crushed stone, compact it and pour the slab. Make sure you use reinforcing. As for the ratproofing...I know nothing about that.

Yup do this one!

 

[dtbingle]

I wouldn't pour a slab them cover it with a wood floor. Seems like a waste of money to me. I would build a wood floor and support it with concrete blocks/spread footings.

Maybe I missed it, but where are you seeing wood floor over the concrete pad? The two options given by the city are basically 1) concrete floor and build walls up from there or 2) put posts or blocks to support a wood floor that's 8" above grade.

I would remove all topsoil/organics, replace with sand or crushed stone, compact it and pour the slab. Make sure you use reinforcing. As for the ratproofing...I know nothing about that.

How necessary do you think sand/crushed stone is? Quick estimate of 10' x 12' x 4" deep = 40 sq ft or roughly 4.5 sq yds. Buying either from Home Depot looks like it'll cost $300-400. Seems a bit steep just for the base of a garden shed. I've seen it mentioned a few times on different sites is that slabs measuring roughly 100 or 150 sq ft basically move with the frost heave and any ground shift, but not sure how true it is. Possibly a pour where ends and center divider are poured a bit thicker to compensate for no gravel?

 

[Stuart in MN]

What the heck satisfies the "ratproofing" requirement for concrete slab? Is this just sealed exterior seams? A 1 ft stemwall? Something else?

I can't say for sure what they mean exactly, but in general a rat slab is just a thin slab (maybe ~2 inches thick) that's enough to prevent rodents from burrowing up underneath the shed.

 

[Disney]

I'd raise it on cinder blocks.

 

[dtbingle]

I can't say for sure what they mean exactly, but in general a rat slab is just a thin slab (maybe ~2 inches thick) that's enough to prevent rodents from burrowing up underneath the shed.

Ahh this would make sense. So basically make the perimeter extend 6" or 8" deep instead of the 4" for the rest of the slab? Then make that deeper perimeter about a foot wide?

It's frustrating how the city codes have misleading or general info regarding simple things such as a shed and getting info over the phone is like pulling teeth

 

[lakeroadster]

We always peeled off the top soil for the slab and an additional 2 ft all around the perimeter. We then rolled out a 3 ft galvanized chicken wire fence on the sub-grade around the exterior of the building, overlapping under the slab about a foot, place the forms, pour the slab, pull the forms, then back fill the perimeter with the top soil that was removed.

This will keep out rats, ground hogs, etc.

As a side note... Make sure the siding hangs over the edge of the slab... otherwise you will have water infiltration issues.

Good luck

 

[D45]

Weed fabric, crushed limestone, wood timbers........rock solid, put down right over the grass


http://www.garagejournal.com/forum/showthread.php?t=244568

 

[captain14]

http://www.garagejournal.com/forum/showthread.php?t=359362&highlight=Pier

My post for pier blocks is #18. We've built 2 shed using these pier blocks , 25+ years later no issues for the floor. Plan for a section of angle iron under the doors so you can place a ramp to run the mowers, etc inside. Or just design a ramp and leave in place. The only drawback it increases the footprint into the yard.

We had to replace 2 lower sections of the T-111 siding on an adjacent shed sine it sat on a concrete pad, stored things against it and I think it mainly failed since it never got a chance to dry out because of no air circulation. The panels just stayed damp. I can feel a soft spot there again in the same area because my dad placed stuff along side again

 

[bcradio]

How necessary do you think sand/crushed stone is? Quick estimate of 10' x 12' x 4" deep = 40 sq ft or roughly 4.5 sq yds. Buying either from Home Depot looks like it'll cost $300-400. Seems a bit steep just for the base of a garden shed. I've seen it mentioned a few times on different sites is that slabs measuring roughly 100 or 150 sq ft basically move with the frost heave and any ground shift, but not sure how true it is. Possibly a pour where ends and center divider are poured a bit thicker to compensate for no gravel?

Depends on what type of native soil you have. If you have decomposing granite soil that is harder than concrete is in many parts of the country (as I do), then you don't need anything under it.