styrofoam and concrete floor - insulation thoughts

[RTcat]

Getting ready to pour a concrete floor in my 50'x 72' pole shed. Somewhere down the road I'll be "enclosing" a corner of the shed for a heated workshop. It will be forced air heat. With regards to forced air heat, is the concept to not let the heat escape down through the concrete, or is it to prevent coldness from coming from the dirt ground up through the concrete?

I'm wondering the best way to insulate floor area where the work shop will be.

Two schools of thought I've heard.

#1 Where the concrete meets the ring board take 1 1/2" styrofoam and cut it in to 16" widths. Dig away the gravel and dirt an place the top edge of the styrofoam level with where the top of the concreate will be. Basically I'd have 16" of foam running down beside the 5'' floor and the gravel dirt below it, seperating it from the dirt on the outside of the building. This prevents coldness from entering into the side of the concrete and the dirt below it.


#2 Place 1" styrofoam on top the gravel base before pouring the floor.

Would doing both be overkill?

Does #2 lead to more likelyhood of concrete shifting/cracking (expansion joints will be cut in)

What's best way to insulate concrete where forced air heat will be used?

Finally, I'll be putting bisqueen (plactic) down on the entire floor to prevent sweating.

Thoughts?

 

[DynoDave]

I'd love to hear from folks on this too. I was concerned that the foam might continue to crush/collapse over time, leading to the slab cracking or shifting, especially where I plan to put the lift. I have never heard of anyone using option 1 above. I planned on the approach in option2. And definitely a vapor barrier.

 

[JohnZ]

I put 10-mil poly (Visqueen) down first, then 4'x8' sheets of 5/8"-thick high-density closed-cell foam with heavy foil on both sides, then poured the 2500 sq. ft. mesh-reinforced 5" slab over that. Did it for two reasons - impenetrable barrier against moisture migration up through the floor, and insulation capability. Built it six years ago - it's always dry as a bone, zero moisture migration, and it's a warm floor in the (cold) winter. I have ceiling-hung forced-air heat. Have cut-in expansion joints (8' squares), epoxy coating, not a crack anywhere after six years.

 

[PAToyota]

One of my jobs we designed refrigerated warehouses. For frozen storage (-20 deg F and below) we'd actually run a double slab - from the top would be a slab, insulation, second slab with radiant heat, insulation, and then the earth below. This was to keep permafrost from forming beneath the freezer and heaving it.

Anyway, they taught me quite a bit about insulating buildings.

In commercial construction we typically run 2" closed cell foam down 3' to 4' at exterior foundation walls and 4' to 6' horizontal. If the space is always heated, you eventually warm up the earth directly below the building and this insulation keeps the heat from "escaping" out the sides.

The question is - will you heat the space continually? If it is always heated, you have this thermal sink of the earth below the building. If you heat it up for a week while you're out there working and then you aren't going to be out there for a few weeks and you turn the heat off, you don't get this buildup of heat. Then you would likely want a continuous layer of insulation under the entire slab. This way, you heat up only the slab and aren't trying to heat all that earth.

When I built my shop, I put in radiant heating tube and knew that I wasn't going to heat it all the time so I put in a layer of DOW SM under the whole slab. This way I can heat up the slab without heating up the ground below.

Back to the refrigerated warehousing. Because we had the insulation below the concrete, this made for a very uniform slab. Some of what causes cracking is settling. But a lot of what causes cracking is stress risers in the concrete caused by sharp edges in the bottom of the slab. The smoother your base, the less chance of cracks. On the insulation, we'd pour 50' to 100' between control joints. A lot of concrete people tell me you just can't do that and not have cracks. I can show you warehouses with robotic picking systems with no cracks and floors +/- 1/16" over 100' - something else they often say cannot be done.

Make sure that you get a closed cell foam - an open cell foam will absorb water and deteriorate underground. This will lead to the settlement, cracking, and other problems that you are concerned about.

 

[imported_banzaitoyota]

For what its worth:

http://www.clearspan.com/webapp/wcs...nsulation&breadcrumb_categoryIds=11238&isDoc=