Frost Protection Shallow Foundation (FPSF) insulation technique

[marzo91]

It's a long read, but pretty interesting........

http://www.cs.arizona.edu/people/jcropper/desguide.pdf

This is the method I used to insulate my new shop. Has any one else done their shop this way?



Basically, no insulation under the slab to take advantage of the constant temp of earth (and "heat bulb") below the slab. The horizontal insulation prevents the frost from entering the ground below the slab.

 

[MN4x4]

See my thread here:

http://www.garagejournal.com/forum/showthread.php?t=83113&highlight=frost

 

[kbs2244]

It is not a new idea.
And it works.
But only if the building is kept heated.
And it is not fool proof.

The problem is the protection if the insulation above the dirt level up to the siding level.
The foam board is attacked by sun, critters looking for a warm place to dig, and weedwackers.
Then you get water infiltration between the foam and the concrete.
That water will freeze if the building is not kept heated.
And that starts a downward spiral of things.

 

[marzo91]

It is not a new idea.
And it works.
But only if the building is kept heated.
And it is not fool proof.

The problem is the protection if the insulation above the dirt level up to the siding level.
The foam board is attacked by sun, critters looking for a warm place to dig, and weedwackers.
Then you get water infiltration between the foam and the concrete.
That water will freeze if the building is not kept heated.
And that starts a downward spiral of things.

Good points. I'm installing a 83% efficient natural gas furnace. Going to try to keep the temp in the 40-45 degree range all winter. I guess the high efficiency furnaces don't work out as well as the 83% at lower inside temps. I'll report back the monthly heat cost per month this winter.

I have metal flashing that covers the top 6" of the foam. I have 3-4" of 2" washed stones on top of weed barrier against the flashing.

 

[Teikas Dad]

When I added my workshop on to my barn a few years ago I did a FPSF. The mason I hired had never heard of one so I printed out the booklet and gave it to him. He tried to tell me it wouldn't pass the building inspection...except....the building inspector was the one who suggested the foundation to me. When I told the mason that he got right to it. I didn't insulate the floor per the instructions. I ran 2" foam board down the sides of the foundation and 2 feet out at the bottom. I got some heavy duty paint that was made for painting foam insulation and slapped it on. It's been protecting the foam for 5 years now with no problem. I heat the workshop with a Hot Dawg heater. I leave the temp set at 40 degrees when I'm not in the shop in the winter. That coupled with 2X6 framing and 10' ceilings and everything is working fine.

 

[marzo91]

Awesome!! I'm happy for you and me.