Thickened edge slab possible on clay soils?

[Shoester]

I'm located just outside of Kansas City, and I'm considering my foundation options when it comes to building a 24x26 detached garage. I think my soil contains fairly high clay content, as it seems to hold/puddle water after lots of precipitation.

With properly installed french drains, removing 8" of soil and bringing in AB3 gravel, would a thickened edge slab (12" thickened edge, 4" slab) be sufficient for this size of building? Or is it necessary to pour footings down 40" below the frost line?

 

[AllDodge]

IMO I would not make the edges thicker then the slab. The slab should be free floating. If the edges are thicker then the slab and the center sinks, it's going to crack. I would pour a footer to 24 inches (not 40) and then pour a floor

 

[Falcon67]

I would look at your local foundation guidelines first. Look on KC's city web site, they may have plan recommendations for detached garages.

We have expansive clay soil here, but no frost line. I used a 12x12 perimeter for my 4" slab with one longways 12x12 beam and three cross 12x12 beams. 1/2" steel ran through the beams and footer with 3/8 on 24" squares in the slab. Slab has not moved around in 5 years.

 

[Falcon67]

Here:
https://data.kcmo.org/Information-B...ab-And-Foundation-Wall-Details-2003/u7zu-wn6p

 

[Shoester]

Here:
https://data.kcmo.org/Information-B...ab-And-Foundation-Wall-Details-2003/u7zu-wn6p

Falcon, I don't care what your wife says...you're a damned good guy.

 

[Falcon67]

Hahaha. Been through that "how're we gonna do that" so I kinda know where to look.

 

[kd3pc]

Many of our garages here are thickened edges and monolthic pour with the floor. Mine is 22x24, steel and mesh that turns down on the perimeter. Should be no problem, as long as the AHJ is ok with it.

Before I built mine, I stopped at almost any slab under construction and ask the concrete guys how and what they did for the slab. I also asked who did the best work for small garages and such. Pretty decent and consistent responses helped a lot when I built later that year.

 

[Radix2]

Since you are in a cold zone, either follow a standard below frost foundation plan or follow a "frost protected shallow foundation" plan (using a thickened edge and insulation under and around ). It would be foolish IMO to follow designs for frost free zones where you are.

 

[JACDes]

since you are in a cold zone, either follow a standard below frost foundation plan or follow a "frost protected shallow foundation" plan (using a thickened edge and insulation under and around ). It would be foolish imo to follow designs for frost free zones where you are.

this !

 

[Shoester]

Since you are in a cold zone, either follow a standard below frost foundation plan or follow a "frost protected shallow foundation" plan (using a thickened edge and insulation under and around ). It would be foolish IMO to follow designs for frost free zones where you are.

Very good points. I took a look at the FPSF concept, and from what I read it seems to only apply to structures that will be constantly heated? Do I have that correct? My garage would only be heated when I am using it.

 

[Radix2]

Very good points. I took a look at the FPSF concept, and from what I read it seems to only apply to structures that will be constantly heated? Do I have that correct? My garage would only be heated when I am using it.

There are designs for both unheated and heated buildings - the unheated designs have more extensive insulation "wings" outside the perimeter of the building to make sure the frost never makes to the building. You will find a chart that gives the dimensions of the insulation based on your specific frost zone.

http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf