Shed Foundation Advice Wanted

[connor77]

Need to replace a 16 x 10 shed that I have with something more meaningful. More like 20 x 16 and with taller walls. I'm in the Northeast (MA) and the most intimidating decision I have right now is what to use for a foundation. I've done a little reading and research and had a quick discussion with the building inspector. If I were to use sonotubes I'd need 20 of them to adhere to code. That's a lot of digging even with a rental tool of some kind. A builder doing some work on a neighbor's house suggested a slab but I don't think that's legal based on needing to go below the frost line. I've seen lots of threads on pole barns but I don't think something like that would apply to me (no horses and don't need anything that big - just storing tractor, yard stuff, misc).

My shed is just a gable style with an adequate wall height so I can get by BX in it without my ROPS hitting something. I do want to use full dimension lumber because I like how it looks and it's obviously beefier. Will probably do joists on 12" center so that there's zero deflection.

Can anyone offer any advice on the best foundation given my location and the dimensions I'm considering (20' x 16' with 7/12 sloped roof).

 

[framer]

Why not pole barn. Sinks some poles you could frame it conventional framing
if you like. A small building to worry about frost line footings.Pour a floor inside when built.

 

[JJT]

Research Alaskan slab, I went this route with my recent 28x42 shop/garage. It's also called a floating slab. Talk to your code enforcement office, he'll tell you what you need to meet code.

 

[MarkV]

The floating slab is a pretty common way to do a shed without having to get below frost line. Of course you need to talk to your building department to see if it is expectable in your area.

MarkV

 

[tommu56]

The hunched slab is the way to go.
also known as frost protected shallow foundation (FPSF)
What will go in there will determine the floor thickness and reinforcing

The outside of the slab would be 6-8" thick 18-24" in all the way around and 3-4" in the center section with wire mesh or rebar reinforcing.

tom

 

[GE222]

In Southern Wisconsin, we have a hunched style slab, 20" thick at the perimeter, and 5-1/2" in the center. The perimeter and center has wire mesh, and the perimeter also has re-bar.

The building is 42' x 48' with 14' sidewalls and 2' eves. After 5 years there have been no issues to date.

The top of the slab is roughly 10-12" inches above grade. I was very careful with the surrounding grade for all water drainage.

I didn't compare the cost on a standard pole building, but if I had to do it again, I would still go this route.

 

[flusher]

Need to replace a 16 x 10 shed that I have with something more meaningful. More like 20 x 16 and with taller walls. I'm in the Northeast (MA) and the most intimidating decision I have right now is what to use for a foundation. I've done a little reading and research and had a quick discussion with the building inspector. If I were to use sonotubes I'd need 20 of them to adhere to code. That's a lot of digging even with a rental tool of some kind. A builder doing some work on a neighbor's house suggested a slab but I don't think that's legal based on needing to go below the frost line. I've seen lots of threads on pole barns but I don't think something like that would apply to me (no horses and don't need anything that big - just storing tractor, yard stuff, misc).

My shed is just a gable style with an adequate wall height so I can get by BX in it without my ROPS hitting something. I do want to use full dimension lumber because I like how it looks and it's obviously beefier. Will probably do joists on 12" center so that there's zero deflection.

Can anyone offer any advice on the best foundation given my location and the dimensions I'm considering (20' x 16' with 7/12 sloped roof).

For a slab, it's the bottom of the perimeter footing (usually 12" wide) that needs to be below the frost line, which in MA is probably pretty deep (36-48"). Here in the North Sacramento Valley, the requirement is 12" deep since the ground never freezes so there's no heaving problem.

So the perimeter for your 16x20 ft shed is 72 ft, which is a lot of digging if you want to use the traditional slab footing arrangement.

I know all about that since I've just finished hand digging two 12"W x 18"D x 36 ft long footings for a 20x36ft metal carport that I'm having installed.





I hand-dug those trenches because I didn't want that nice gravel driveway messed up by a backhoe or skid steer excavator. I'll install rebar tomorrow, call for an inspection (hopefully on Tues) and pour concrete Wed or Thurs weather permitting.

The sonotubes look attractive to me. I assume they're 12" dia. Your problem is drilling 3-4 ft deep holes. That can be challenging even with stout equipment if the ground is rocky (I mean large New England rocks, not just gravel). My neighbor hit hardpan about 30" down while trying to drill 12" dia x 42" deep holes for a cattle gate. He was using a Bobcat with a hydraulic PHD and struggled to get through that layer.

Another possible option is to design a portable shed, one that is supported on horizontal 6"x6" pressure treated beams. That way you only have to dig shallow trenches (maybe 6" deep) and fill them with gravel to provide some drainage under the PT beams. You need to check with your county building department to see if this type of construction is allowed.

 

[AlbertaDan]

Need to replace a 16 x 10 shed that I have with something more meaningful. More like 20 x 16 and with taller walls. I'm in the Northeast (MA) and the most intimidating decision I have right now is what to use for a foundation. I've done a little reading and research and had a quick discussion with the building inspector. If I were to use sonotubes I'd need 20 of them to adhere to code. That's a lot of digging even with a rental tool of some kind. A builder doing some work on a neighbor's house suggested a slab but I don't think that's legal based on needing to go below the frost line. I've seen lots of threads on pole barns but I don't think something like that would apply to me (no horses and don't need anything that big - just storing tractor, yard stuff, misc).

My shed is just a gable style with an adequate wall height so I can get by BX in it without my ROPS hitting something. I do want to use full dimension lumber because I like how it looks and it's obviously beefier. Will probably do joists on 12" center so that there's zero deflection.

Can anyone offer any advice on the best foundation given my location and the dimensions I'm considering (20' x 16' with 7/12 sloped roof).

Up here in northern Alberta Canada where ground heaves regularly we use a floating slab. My garage is 22X26. The slab is a min. of 5 1/2" thick. It's 11years old and hasn't cracked yet. I have had my full size truck in there,(weighs about 6000lbs) a couple of motorbikes and the wife's convertible, but it is tight. I spoke with a couple builders before I built it and they recommend NOT using the wire mesh because it doesn't have the same re-inforcing ability as re-bar. If your floor does crack, the mesh is only a thin wire holding the crack together.

When I built mine I made stub walls on top of the slab. They are about 5-1/2" thick by 5-1/2" high. I did this to keep the snow and melt water from getting to the sheeting under the siding and from getting into the garage in the spring.

My son built his garage about 4yrs ago and he used the wire mesh with only a 3-1/2" thick floating slab. Both front corners sunk and his floor cracked. This cracking was from the frost heaves.

I don't know what the code is there but the floating slab is exactly that. It floats on top of the ground without footings.

Do your self a favor and make the walls 10' if you can. Mine only has 8-1/2 and a lot of times its too low. And make sure there is a very slight slope towards the door. When you park your tractor in there after clearing snow all the melted snow will run back under the door.

 

[carpenter383]

If you're already planning to pour a concrete floor, then a floating slab would be the way to go. If you're planning to have a dirt or gravel floor, then the cheapest would be posts.

 

[mmurphy]

You have some good advice here to look at and take to building code inspector. If you can not use a floating slab in your area, (I would bet you can if you check in to it) you could run holes down in ground fairly straight and cut sonotube to what ever length you would need so it is the only part above ground and than stake it in place to pour your holes. If you went pole style you would have less holes to dig than 20, is that a code thing over there about all the holes and sonotube bit?