Frost wall vs Floating Slab?

[ColeHamilton2615]

Hi All,

I'm frantically planning to build a 30x40 stick built garage before winter hits. I talked to a concrete contractor about getting me on his schedule and I'm locked in, but he thinks we can just do a reinforced concrete slab with thickened slab edges. Has anyone else done something like this in a cold climate like Wisconsin? How has your shop fared?

Half the shop will be insulated and heated half the shop wont.

Thanks,

Cole

 

[GMCGarage]

Most of the time slab on grade is more for where you dont get frost heave. I would suspect you would get alot of frost in Wisconsin. Reasearch why type of sub base you would need for the slab on grade.

 

[cre73]

I completed one 20+ years ago here in central Illinois. Still standing without issues. Last time I peaked inside when driving by floor still looked almost perfect. I used lots of rebar and woven wire panels in it when we poured the floor.

 

[ColeHamilton2615]

That's good to hear! How deep and wide were the slab edges? I'm thinking 24" deep x 18" wide. Did you use rebar for the foundation and to tie into the slab and the WWF from there?

 

[Copymutt]

Avoid monopour(slab on grade) if you have expansive clay soil.

 

[ColeHamilton2615]

Soil is very sand where I am located.

 

[klassenl]

I live in sandy-clay soil area. It's gets cold here in Alberta. My slab is around 850 Sq feet. 16x16 thick edge with 6 inches in the middle and it hasn't moved at all. It's my belief that the mono slab option is the most economic solution.

 

[finn]

I’m north of Wisconsin. Thickened edge slab on grade is common here, but it probably depends on local soil conditions.

My garage floor, slab with thickened, reinforced edges, was built in 2003, and there has been zero issues.

Did I mention it gets cold up here? The frost line is down about 5’ for water pipe protection where there is no snow protection to insulate pipes.

 

[ColeHamilton2615]

Thanks Everyone,

I feel more comfortable now that some people have this and haven't had issues.

Does anyone have a shop that is partially heated and partial cold storage? How did you or did you thermally break the slab between the heated and not heated portions?

 

[joe_padavano]

One more post on the floating slab. I live in Northern VA. Very clay soil, and frost line is about 3ft down. I built a garage with a floating slab. I laid in perforated drain piping under the slab and about 8" of gravel before the pour. No issues with frost heaves or cracking in 15 years now. If the base under the slab is well drained, there's no water to freeze.

 

[Jeffksf]

Mine was fine in many Cleveland winters, I used rebar in the thickened area, mesh in the slab.

 

[The Maxx]

I've seen plenty here in southern Wisconsin. Holding up well since we love us a lot of rebar

What I can't say is soil conditions that may be better for one type of construction over another.

 

[MJD1]

Many in Wisconsin done that way. At one time 2' on the side, buried and 2' out of 2" pink foam was considered a frost wall here.

 

[ConCretin]

I agree with those who've commented that mono-slabs work fine in cold climates and have the added benefit of being more cost effective. As long as the existing soils drain relatively well you should be fine. I have a 28 x 32 garage on a 4" slab with 12" thickened edges. I put a couple #5's in the bottom of the haunch and #4's @ 24" in the slab.

My only concern in your case is the fact that part of the structure will be heated and some won't. This could lead to some unwanted differential movement. I'd put 2" of rigid insulation under the whole structure and extend it out a distance roughly equal to your local frost depth around the perimeter.

The insulation will retain the natural heat from the ground and keep the frost out from getting under the structure. Without it, frost is likely to get into the subgrade under the un-heated sections but not the heated area leading to differential movement.

 

[ColeHamilton2615]

Thanks everyone, LlWillysfan, that was my exact concern. I'm going to draw up a section quick to make sure i'm on the same page.

 

[ColeHamilton2615]

Here is my proposed foundation section. 2" underslab insulation under the entire building that continues under the thickened edge and out 4' past the wall. I'll break the slab and edge at the interior wall between heated and unheated and put 2" rigid between the slab edges. This should bring the frost line up to the underside of my building and I shouldn't have to worry about any heaving.

https://imgur.com/a/11IwVuE

 

[rayra]

Hi All,

I'm frantically planning to build a 30x40 stick built garage before winter hits. I talked to a concrete contractor about getting me on his schedule and I'm locked in, but he thinks we can just do a reinforced concrete slab with thickened slab edges. Has anyone else done something like this in a cold climate like Wisconsin? How has your shop fared?

Half the shop will be insulated and heated half the shop wont.

Thanks,

Cole

yeah... No. That's not going to happen. No way in hell.

Pretty sure you won't get away with slab-on-grade in WI, not unless you are doing all this without permits.

And doesn't 'winter' start there in about a month?

 

[Ryanjax]

Do a search for frost protected shallow foundation (fpsf). I did my shed like that and it worked pretty well. I think it was 16 inch thick and edges and then a 4 inch slab with 2-inch foam underneath and extending out 2 Ft.

Sent from my SM-G960U using Tapatalk

 

[TurnipTruck]

If your soils drain well (not much or any clay), the monopour “Alaskan” slab works great.
I have never seen a frost wall shop here in Alaska. All I have ever been in are floating.

 

[kbs2244]

" If the base under the slab is well drained, there's no water to freeze. "

This is the basis for the rock fill under RR tracks;
(For some reason they call it "ballast.")
They measure it by the mile and cannot afford to have frost heaves on the exposed to the weather tracks.

It has been working in all kinds of weather for hundreds of years.

 

[Stuart in MN]

They're very common in Minnesota, my detached garage was built on a slab over 25 years ago and is still working fine.

 

[Stuart in MN]

yeah... No. That's not going to happen. No way in hell.

Pretty sure you won't get away with slab-on-grade in WI, not unless you are doing all this without permits.

And doesn't 'winter' start there in about a month?

And you're in Los Angeles, giving advice about building in the frozen North?

 

[ConCretin]

Here is my proposed foundation section. 2" underslab insulation under the entire building that continues under the thickened edge and out 4' past the wall. I'll break the slab and edge at the interior wall between heated and unheated and put 2" rigid between the slab edges. This should bring the frost line up to the underside of my building and I shouldn't have to worry about any heaving.

https://imgur.com/a/11IwVuE

You've got the right idea. In real world conditions, the vertical insulation on the inside of the haunch will end up at more or a 45 degree angle rather than vertical as shown in the sketch. There is just no way to excavate native materials or place and compact fill that precisely. The rigid insulation will never sit perfectly flat but the more care you take the fewer voids will be created.

 

[ConCretin]

yeah... No. That's not going to happen. No way in hell.

Pretty sure you won't get away with slab-on-grade in WI, not unless you are doing all this without permits.

And doesn't 'winter' start there in about a month?

On what do you base this statement?

 

[ColeHamilton2615]

Thanks LLWillysfan,

I think I’ll also put the insulation directly under the slab and gravel under that with a 6 mil vapor barrier in between. Do you think the thickens slab edge is overkill? I’ve talked to a couple other people who have done 18” deep by 18 wide.

 

[ColeHamilton2615]

If your soils drain well (not much or any clay), the monopour “Alaskan” slab works great.
I have never seen a frost wall shop here in Alaska. All I have ever been in are floating.

Thanks TurnipTruck! I check my soil in the GIS and it says it is excessively drained sandy loam soil so it should be perfect for this application!

 

[spudley]

Poured a 4-5" slab on grade last year in northern Wisconsin. We thickened the edge to approx 20" deep and cut the angle about 20" in from the edges. Used three rows of #4 rebar in the thickened edge area with a 2X2' pattern of rebar through the slab.

The soil is 95% sand.

Had one of the coldest winters on record with several days at -30 degrees and so far, it's all good.

I think your floor will hold up fine if your soil drains well, but if I did this again I'd put in a radiant in floor heat system.

 

[ConCretin]

I think I’ll also put the insulation directly under the slab and gravel under that with a 6 mil vapor barrier in between. Do you think the thickens slab edge is overkill? I’ve talked to a couple other people who have done 18” deep by 18 wide.

Thickening the edge to 12" is plenty - you could even get by with 8" but a little extra concrete is cheap insurance.

When I did mine, I laid down 24" wide form panels to form the perimeter of the slab. I placed a 12" thickened slab against the bottom and then dropped a 12" inside form on top of the slab and placed a curb wall against the top. A curb wall is kind of nice as it lifts your wood framing off the ground and slab surface.

 

[ColeHamilton2615]

My plan right now was to do 1 row of CMU for the wood framing to sit on. More work that I can do and less that I have to pay to have done!

 

[SwampCat]

Another N.E. Wi. garage monkey here. Put the radiant floor heat in the WHOLE garage. You will NEVER regret it. If you have natural gas, I can hook you up with a boiler for cheap if you are in the area. You get ONE chance to do this right, so get all of your loons in a row.

 

[TractorJeff]

I have thickened edge!
See my location!
I think my local Inspector specified the thickness of the edge and the number of rebar used?

 

[maxpat82]

monolithic slab is very common here in Quebec too. (thickened edge)

I went with a frost wall for mine (28x44)

costed me 30K compare to what would have been 15K for a monolithic.(all the concrete work, ground work etc was included in both)

 

[Diesel Dan]

My plan right now was to do 1 row of CMU for the wood framing to sit on. More work that I can do and less that I have to pay to have done!

Having 1-2 rows of block to keep the wood away from the ground is a good idea, imo. When you do that make sure you have rebar or long J-bolts that extend all the way through the block into the "footer" to tie everything together.

When we lived in NW Wisconsin and were hit with straight line winds in excess of 100 mph and a neighbor lost their garage. It took the top row of block with it since the j-bolts didn't go into the slab. Only thing holding the garage down was gravity and a mortar joint.....and they lost. Every contractor and inspector looked at me funny when I had vertical rebar every 4' on my new build, kept saying only needed when exceeding 10 course high.