Pipes above or below insulation with unusual insulated slab on grade

[rural_engineer]

My house is going to have a somewhat unusual slab on grade arrangement. The slab has turn down footings and is frost protected, so the footing concrete extends only 12" below grade. Underneath the entire house, just below the footings, is 5" of structural EPS foam. Its strength is such that it's expected to compress less than 1% under weight of the house at the footings. Between the foam and the slab is nominally 15.5" of compacted crushed stone or other structural fill.

I'm wondering whether I can run my waste pipes through the fill above the insulation, and then drop down below the insulation when I need to pass under the footings? Other than a length limitation from the available height, are there any concerns from putting the pipes in this space?

All work will be done by a plumber. I'm just getting everything figured out in advance for quoting and planning. The house will be on an in-ground septic system near Rochester, NY.

Cheers,

John

 

[Patrick McAllister]

John, I have the same problem. I'm using "Modified slab on Grade" with a frost protected foundation. Also called a "Hunched Foundation". I could use some help. We could put the water pipes in a sleeve, or bury them below the footer.