Boiler shed construction question - do I need a slab/poured foundation?

[MrEd]

Question for you knowledgeable builder types...

I have gone back and forth about 10 times between tarm in the attached garage(no longer used as a garage) and a new, to-be-built, combo boiler room/woodshed that would be 30 or so feet from the house. The cost of putting up the shed keeps putting me off (underground pipes etc), but I figured I need to make a firm decision soon, so I need to figure out a full cost of both options and then decide.

Question for today is: If I built a seperate shed (approx 10x14 for the boiler and a few days wood), would it need to have a full concrete wall construction+cement floor? In my area, frost depth for code purposes is 4 feet and for most outbuildings I go with drilled holes, footers and sono-tubes, and then a wood platform on top - but with an almost 1500lb boiler all concentrated in a 2x4' area, I have concerns about the weight. I am also not sure if I use piers to support just the walls and roof, if it is still possible to pour a concrete floor without the frost walls - my guess would be no.

Suggestions? I'd like to be code compliant, although in my area outbuilding construction oversight is pretty lax...the living space is the inspectors main area of concern.

 

[pbvermont]

you could put it on a floating slab, also called slab on grade-beam. Pretty easy to do with a slab that small. Forget the sono-tubes, and footers. People put mobile homes on these all the time.

 

[verne]

you dont need a foundation at all you could put in a standard shed and add an extra floor joist to support the load . In ny you can no longer do an Alaskan slab. you could go the sonotube route, frame off the top and poor slab inside or build it pole barn style; 48" holes compacted concret mix, 4x6 post and poor the floor on compacted base. they all will work and weight isnt an issue. I just finished building a 24x32 pole barn to house my eko 40 and 1000 gal storage tank

 

[MrEd]

I understand what a pole-barn type construction is, but why won't the slab itself crack/move if it is not surrounded by a frost wall? I was always under the impression that in order to put down a slab that would last, you would need a frost wall all around the outside.

Clearly, if I could build a pole barn type setup, and pour a slab after its done, that would be easy to do - but will it last?

 

[verne]

I understand your thought , but if you have a good base , as in gravel etc it would take some serious frost to get under the slab and move it . also you will have a boiler inside keeping buildind warm. before recent code changes we built many garages and houses on the alaskan slab . also I have built many pole barns over the last 20 years and never had an issue. any concrete floor will crack , that is why control joints are a must .

 

[Chris S]

Verne,
I was unaware Ny prohibited the "alaskan slab" I just built one.
Educate me please

Chris

 

[DenaliChuck]

The "Alaskan" slab should be called the "Euro-slab". They were doing it at our latitude long before we started!

It is important to insulate very well under the slab or you lose a huge amount of heat to the ground. Even well insulated, enough heat is lost to the ground to prevent frost heaving, but there is a slight risk if you let the building go cold, but I don't worry since we sit on well drained gravel and there is no moisture to freeze and heave. It is especially important to insulate the outside perimeter either 4' vertically or at a 45* angle to keep the heat under the building. I have 4" of blue foam under my whole slab, except under the footer portion and it serves us well. Of course this is in Alaska, and our temps are a wee bit colder than ya'll in the south.

DC

 

[verne]

Chris as usual inspectors choose to enforce what they like,. I have a friend up north who just built one also. I asked when i got the permit on my barn if i could do Alaskan he said no. I have not found a municipality any where near me that allows it . I have worked as a project manager for the last ten years in the Hudson valley.

 

[Chris S]

So you're saying that the codes changed recently- and not all municipalites have caught up with it yet?

But a pole barn with a slab is still allowed. I would much rather have a floating slab. My detached building for my boilers will have conventional footings & frost walls, but we sometimes build detached 2 car garages with floating slabs. The Company that's on the radio in the Hudson Valley that builds sheds and garages ( with that catchy jingle) builds all of their garages that I've seen with floating slabs

Chris

 

[verne]

chris the company with the" jingle "
delivers a pre built shed that could be put on a stone pad . It is a moveable structure .poughkeepsie for one ,requires 8" of sub base under any shed. we have been pouring slabs for generations on compacted gravel . The code change isnt even that recent. my father lives near saratoga . alaskan not ok .the reason you can build a pole barn with a slab is that the poles go below frost,so the building isnt going to move .,My friend borrowed my codebook . when I get it back I will give you reference. The original post asked if you needed a full foundation for garage out -building, the answer still is no. The concern following was if the slab floating would hold up. the answer is with compacted sub base YES. I have a 40 year old barn on my property with a poured slab and it is flat and even. from what I think we were talking about about was a building to house a boiler and wood storage . If you want to sink that much money into an out building, so be it.If you have well drained gravel it cant hold moisture , so it cant freeze so it cant heave. chris the shed company also install barns on floating slabs, not a permant structure. more to the point that you dont need a full foundation for an out building