Plumbing under frost protected shallow foundations – GreenBuildingAdvisor

Frost-protected shallow foundations (FPSF) are designed to avoid deep footings below the frost line by utilizing insulation to raise the frost depth around the building. This allows for shallower foundations, potentially saving on excavation and concrete costs. The attached image illustrates the frost line being raised due to this construction method and a similar illustration is provided in ASCE (American Society of Civil Engineers) 32, “Design and Construction of Frost-Protected Shallow Foundations”.

Section P2603.5, Freezing, of the 2018 IRC requires the water, soil and waste pipe to be protected from freezing. The frost depth in my area is 42 inches but the utilization of a frost-protected shallow foundation raises this depth to the bottom of this foundation’s insulation. Therefore, can one install plumbing under a frost-protected shallow foundation less than the typical frost depth (e.g., 42 inches) and without insulation due to this type of foundation?  I do know the water service is required to be 6 inches below the frost depth… so it would need to be 6″ below the elevation of the insulation. 

Note. I am an inspector so I can only require code compliance. I may recommend but cannot mandate something not written in a IRC. I try very hard to keep personal opinions to myself.