Fine Homebuilding article on under slab insulation

[Jackfre]

This is a good reference article for those planning to pour a new slab. Worth a look.

 

[LB-1911]

This is a good reference article for those planning to pour a new slab. Worth a look.

This article or another?

Insulating a slab on grade
Issue 245 - Aug/Sept 2014
http://www.finehomebuilding.com/2014/07/09/insulating-a-slab-on-grade

 

[theoldwizard1]

From http://www.finehomebuilding.com/2014/07/09/insulating-a-slab-on-grade

This image says it all

Note the following

• Thermal break between foundation wall and slab.
• Foundation wall is several inches higher than finish grade *
• Interior finish wall is held up off of the floor.
• Sealant between floor and footer.

* Many building code require a solid 6" "curb" (vertical extension of the foundation wall) ABOVE the finished height of the floor.

 

[manufacture]

The article the OP is referring to details the construction of a garage foundation usually called a frost protected shallow foundation. Max digging depth for continental US would be something around 24 inches in the colder zones. The foundation is comprised of an edge thickened slab sitting on a continuous layer of insulation (usually foam board) which also extends out some distance from the perimeter of the foundation. The insulation traps the heat of the Earth moving the frost depth up past the bottom of the slab. They have the advantage of needing much less excavation thant typical frost wall and slab foundations and can also be done with just one concrete pour instead of three.

The article in Fine Homebuilding is good and was written from the perspective of a contractor who used the frost protected shallow foundation system when he built his own garage.

 

[theoldwizard1]

Max digging depth for continental US would be something around 24 inches in the colder zones.

In SE MI, I am pretty certain the codes call for 40"-48" depth.

 

[Diesel Dan]

While I was in N.W. Wisconsin they lowered the depth to 54".

 

[matt_i]

In SE MI, I am pretty certain the codes call for 40"-48" depth.

The article is in FHB # 262, Nov 2016, not the same as the diagrams above.

Note that the Frost Protected Shallow Foundation is not the same design as traditional trench- or pad- footings designed to simply go under the 100year frostline.

The tradeoff in my mind is there's more detail work in the FPSF foundation in the earthwork, the offset slab-form and, there is the cost of the foamboard, but you don't work down in muddy trenches setting block or setting up forms to pour.

Also you have to have your research inline and present the ASCE document 32-01 to your building department at the "plan review" stage, so they won't redline your drawings.