Thickened Slab Question

[edez]

Hi everyone-

I am building a small garage (24' x 24") in north central Wisconsin. I am interested in putting second floor storage space above (5' knee wall/dormer on one side). This will be for storage and bathroom. The concrete guy is pouring a 12" wide by 10" thickened edge with 4" floor with radiant heat.

My question is whether or not this thickened edge will be enough to support the second floor space.

Thanks in advance.

 

[mike93lx]

What's being done for base prep?

 

[edez]

I had a guy come last year and do the base prep. He brought in about ten yards of sand and compacted it. He said sand was fine for the base.

 

[The Cobbler]

local codes would be a better resource for that question I think.

 

[BillK]

I had a guy come last year and do the base prep. He brought in about ten yards of sand and compacted it. He said sand was fine for the base.

What does your concrete guy say about that ?

 

[mike93lx]

I had a guy come last year and do the base prep. He brought in about ten yards of sand and compacted it. He said sand was fine for the base.

Compactable sand is a material I haven't seen before.

 

[txvwnut]

local codes would be a better resource for that question I think.

What he said, plus contact your building manufacturer and let them do the engineering and load calcs for what you want to do. My building is 24'w x 26'l x 20'h and had a required perimeter beam of 12"w x 18"d.

 

[edez]

Thanks for the replies. I am going to call the local office today and ask. I have tried to ask my concrete guy, but he seems very difficult to get in touch with.

 

[Tim in Indiana]

Thanks for the replies. I am going to call the local office today and ask. I have tried to ask my concrete guy, but he seems very difficult to get in touch with.

Welcome to dealing with Northern Wisconsin contractors. Call 10, maybe 3 will reply, maybe one actually gives you a quote. You're really lucky if one shows up to do the work.

 

[edez]

Welcome to dealing with Northern Wisconsin contractors. Call 10, maybe 3 will reply, maybe one actually gives you a quote. You're really lucky if one shows up to do the work.

That's been my experience for the last year. I finally got a concrete guy to call me back and I felt like I won the lottery. He promised to be there in June, now he's saying August.

I have a feeling that I will be doing this myself. That's why I posted here. Wanna make sure I get it right.

Thanks for the reply.

 

[dcg9381]

The concrete guy is pouring a 12" wide by 10" thickened edge with 4" floor with radiant heat.
My question is whether or not this thickened edge will be enough to support the second floor space.

In my part of the woods we call these "perimeter beams" (concrete).
The question to "is it enough" can really only be answered with a perc test on the soil and concrete engineering. Which is gonna cost a few thousand.

The other way to do it (and I've done a much larger shop this way) - you build to typical local design for concrete and building type, assuming the soil type is the same. If he's done other buildings, same area, same soil, and they have no major foundation problems after years, I'd call that a success. But it's not an "engineered foundation".

We've got a 5" slab up north that has no beams. It's a fiber cement slab. Underlying soil is mostly sand. It was just fine for a 2-story home.

YMMV....

I have a feeling that I will be doing this myself. That's why I posted here. Wanna make sure I get it right.

Have you done concrete before? I know that I'm not good enough at it on the finish and slope side, but others have done bigger. Around here a 24x24 would require 2 people to be working on it at once...

 

[edez]

In my part of the woods we call these "perimeter beams" (concrete).
The question to "is it enough" can really only be answered with a perc test on the soil and concrete engineering. Which is gonna cost a few thousand.

The other way to do it (and I've done a much larger shop this way) - you build to typical local design for concrete and building type, assuming the soil type is the same. If he's done other buildings, same area, same soil, and they have no major foundation problems after years, I'd call that a success. But it's not an "engineered foundation".

We've got a 5" slab up north that has no beams. It's a fiber cement slab. Underlying soil is mostly sand. It was just fine for a 2-story home.

YMMV....


Have you done concrete before? I know that I'm not good enough at it on the finish and slope side, but others have done bigger. Around here a 24x24 would require 2 people to be working on it at once...

Thanks. I like your approach. I spoke with a local contractor yesterday and he said that the design as quoted was fine for the area. So, not "engineered" but works.

I have done concrete before, but not this size. Have plenty of help that is younger, stronger and more experienced than me,

 

[gmcgeo]

A 10" deep edge on undisturbed soil can handle a typical one story structure just fine
But for a second story even a partial one you’re adding about 50% more load on the walls
In cold climates like Wisconsin frost heave is a concern Monolithic slabs without deep footings don’t extend below frost line so any extra load increases the risk of movement if the soil isn’t well compacted and drained


Local code in Wisconsin typically requires
Frost protected shallow foundation (FPSF) or
Continuous footings below frost depth (48”+ in North Central WI) for anything with habitable space

A 10” thickened edge does not meet frost depth requirements for a heated habitable structure unless it’s specifically engineered as an FPSF


For an unheated garage with light attic storage your thickened edge is fine
For a heated space with a bathroom which makes it habitable space local code likely requires a deeper foundation
If you put a true second floor with even partial living space the slab edge may not be adequate especially for Wisconsin frost conditions

 

[edez]

Thanks. I have been think that FPSF might with a footing twice as large as my wall and 12" thick might be the better way to go. Space won't necessarily be habitable, but with the bathroom, I understand it may be considered so with the code.

I appreciate your reply and comments.

 

[Mezz2006]

Not sure where in Northern WI you are, but I might be able to recommend some other contractors.
In my area of WI, most detached garages (accessory structures) of that size and larger, both heated and non heated, are thickened edge/slab on grade/mono, mine included (44x56x16.5 with future loft). I think mine is 16"x16", would have to check. My parents cabin with loft second story (24'x28'), all habitable space is ~12x12 thickened edge, insulated under slab, not the full FPSF.

 

[billconner]

Just checking IRC, FPSF requires thickened slab 16" below grade in northern WI. I think only 12" wide.

 

[edez]

Not sure where in Northern WI you are, but I might be able to recommend some other contractors.
In my area of WI, most detached garages (accessory structures) of that size and larger, both heated and non heated, are thickened edge/slab on grade/mono, mine included (44x56x16.5 with future loft). I think mine is 16"x16", would have to check. My parents cabin with loft second story (24'x28'), all habitable space is ~12x12 thickened edge, insulated under slab, not the full FPSF.

Thanks, any contractors you can recommend for the build would be great. I've got a concrete guy coming in early August and am going with his design as he does his in the area and I believe knows best. Please send any names as we are almost neighbors-you in Clintonville and me in Gresham. Really appreciate the reply.

 

[Mezz2006]

Thanks, any contractors you can recommend for the build would be great. I've got a concrete guy coming in early August and am going with his design as he does his in the area and I believe knows best. Please send any names as we are almost neighbors-you in Clintonville and me in Gresham. Really appreciate the reply.

Sent you a message.