I want to put a piece of 2" foam around the perimeter of my pole building slab, capping the edge of the slab and going down 2' for a frost barrier. I see 2 options for where to put it, inside or outside of the mud board. Inside, I would 45 the top of the foam and bring it right to the top of the slab. The downside to this as I see it is I would have to wrap each 6" post individually if I want an unbroken barrier. Is that worth the trouble? Or I could go right outside the mub board which would require a flashing over the top of the foam and 2" foam would stick out further than the bottom of the siding. How is this typically done? (Slab on grade with pex)

If I am not mistaken your post if wood would be equal to R-1 per per inch. The foam is about R- 4.5 per inch.
I have also heard of placing a horizontal band around the perimiter as well. Why not continue the insulation in the core of the shop? or is the building to large to be cost effective?
I just threw this question to Morgan (Badger), worded differently, perhaps he will see this and reply. Seems like a lot of downward heat loss/wast in an uninsulated slab.
Dan

I should have included more info, building is a 4800' commercial shop in North Idaho and will be heated with an outdoor wood fired boiler. I do plan on insulating the core of the shop floor also, or at least the outer 4'-8' of it. My thought behind the 2' vertical foam was to stop frost from migrating underneath the insulated slab. Or would that be better accomplished with some kind of umbrella or wing insulation outside the building?

Thanks for the help,
Chris.

Chris,
Is this an existing building, or one that about to be built?
The reason for insulation around the perimeter is to protect the foundation, and prevent frost heave on the foundation. WIth a properly constructed pole barn, posts are set below the frost line to eliminate frost heave effects. Generally, underslab insulation turned up on the inside of the splashboards should be sufficient for insulating the floor.
However, if the building is not yet built, use a 2" trencher to cut a 24" deep line directly under the line of the splashboards. Then drill your post holes, and set your posts. Then, before installing the splashboards, slide the insulation into the trench flush to the bottom of the splashboards. Then insulate the inside of the splashboards with the same insulation allowing it to overlap the board in the trench by a couple inches.
This will provide a continuous band of insulation in all areas except the point where the splashboards attach to the posts. You can then wrap the posts with insulation to complete the process. Though this last step isn't absolutely necessary as the wood posts will provide some protection for the slab by themselves without the added insulation.

International residential code shows a diagram of this detail. All heated slab-on-grade foundations must be frost protected, from top of slab to bottom at least 1' below grade and then out horizontally to stop frost from migrating under the slab. The distance out horizontally is determined be climate. They do not require you to insulate under the slab which seems kind of stupid to me just around the perimeter and out several feet. Here in MA I go at least 3' beyond the slab with the horizontal insulation as well as up the perimeter and under the entire slab as well. You can never have to much insulation, you cannot add more later and the stuff really isn't that expensive. The 3" of high density geofoam I used cost $1 sq/ft. Well worth the savings as shown on the energy model. It is proven that heat wants to move toward cold, right? Then if the ground is colder that the space being heated some of your heat will travel down into the earth below if uninsulated. Not really where you want your heat to go.

Tom Pittsley
[email protected]
www.eebt.org

Wes, If I turn my insulation board up against the splashboard, won't I be in danger of allowing termites to tunnel through the EPS and reach the juicy lumber inside the walls?  This invasion would be invisible from inside or outside.

Rick

All the answers are here - be it from different sources.

The answer is: the frost doesn't care how it gets it. Frost is just a constant freezing temperature soil that tends to stay at that sub-freezing temperature for a good part of the season. With this constant low temperature heat transfer can be significant. This is why the perimeter insulation is the most effective (and why sub-slab insulation is often ignored in commercial buildings).

Pole barn posts are normally installed below the frost line as suggested (like a telephone pole) and need not be protected (termites don't like frost). So your original idea is correct. I come to the interior of the poles with two inch EPS 4" if you want to go green. (Too much insulation is just that, and wasted).

Come "in" to the building 2 feet (the frost line for Coeur d'Alene) and you are all done. I insulate the sub-slab when the inside design temperature is more than 20% above the "Deep Earth Temperature" (50°F in N. Idaho). Office areas get 2" EPS just for good measure and structural integrity to stand up to foot traffic.