Soil swelling on one side of a Non-Isolated Void System can create net horizontal forces that push Non-Isolated Void Systems and damage plumbing.

Designers need to also carefully consider the effects of swell/shrink cycles on the deformed shape of non-isolated void systems.

In summary, the problem is that an unprecedented and possibly unobtainable level of inter-disciplinary testing and design coordination, plan review and plumbing inspection would be required on each project between the Geotechnical, Mechanical and Structural Engineer to properly protect plumbing using non-isolated plumbing approaches that have been used. A Plumbing Inspector does not have the ability to verify this occurred.

Some of the relevant “Basic Principles” in this document indicate that protection of plumbing from expansive soil is a health, safety and welfare issue.

Principle No. 9: The piping of the plumbing system shall be of durable material, free from defective workmanship, and so designed and constructed as to give satisfactory service for its reasonable expected life.

Principle No. 18: Where a plumbing drainage system may be subjected to backflow of sewage, suitable provision shall be made to prevent its overflow in the building.

Principle No. 19: Plumbing systems shall be maintained in a sanitary and serviceable condition.

Principle No. 22: Sewage or other waste from a plumbing system which may be deleterious to surface or subsurface waters shall not be discharged into the ground or into any waterway unless it has first been rendered innocuous through subjection to some acceptable form of treatment.

Explicitly requires protection of plumbing from expansive soil and defines when expansive soil is present.

Allows buried plumbing under Slabs-on-Ground.

Requires complete isolation of plumbing under Slab-on-Crawlspace and Slab-on-Voidwork: “It shall not be permitted for the plumbing, hangers and supports below the slab or below the framing to be in contact with soil or any assemblage of materials that is in contact with soil within the active zone.”

Exception 1 allows buried pipe for drainage of crawl spaces

Exception 2 allows attachment to piers if the plumbing, hangers and supports are otherwise isolated.

We recommend Mechanical/Plumbing Engineers immediately cease and desist the practice of allowing Non-Isolated Plumbing (Buried Plumbing or Non-Isolated Void Systems) under Slab-on-Voidwork or Slab-on-Crawlspace foundations, regardless of whether the IPC or UPC applies or whatever edition applies, whatever the geotechnical engineer estimates to be the probability of movement occurring, whatever the building official will allow, and however hard the owner demands to reduce the initial cost of construction and claims they will accept the risks of damage that would requiring extensive and repeated maintenance.

We recommend Mechanical/Plumbing Engineers immediately begin complying with the new provisions in the 2024 IPC (provided in this presentation) for protection of plumbing from expansive soil, which is also recommended by the Geoprofessional Business Association:

Non-Isolated Plumbing is allowed under Non-Isolated Slabs

Isolated Plumbing is required under Isolated Slabs

In regions where expansive soil is common, we recommend Authorities Having Jurisdiction adopt the new language in the 2024 IPC for the protection of plumbing from expansive soil.

Alternatively, where expansive soil is present and slabs will be isolated from the expansive soil, we recommend Building Officials require a single, comprehensive report be submitted by a combination of a qualified Geotechnical Engineer, Structural Engineer and Mechanical/Plumbing Engineer, providing analytical justification showing how the plumbing will not be over-stressed or over-strained if the possible expansive soil movement and expansive soil swell pressures predicted by the Geotechnical Engineer actually do occur.