Does the ASPE PEDH apply to expansive soil even though it does not mention expansive soil by name?

Yes. The ASPE PEDH requires mechanical engineers to design for 'known natural phenomena such as earth movement' — a category that encompasses expansive soil, which causes earth movement through swelling and shrinking. The section does not mention expansive soil by name for the same reason it does not mention collapsible soils, frost heave, or underconsolidated fill — it uses general language intentionally broad enough to cover all site-specific natural phenomena identified in geotechnical reports. Reading the section so narrowly as to exclude expansive soil while including only seismic forces would contradict the section's clear intent to require plumbing engineers to coordinate with geotechnical and structural engineers and design for the same phenomena the structure is designed for.

How does the ASPE PEDH establish that non-isolated plumbing under isolated slabs does not meet the standard of care?

When a structural engineer designs an isolated slab — such as a slab-on-voidwork or slab-on-crawlspace — specifically to isolate the building structure from expansive soil movement, the ASPE PEDH standard of care requires the plumbing engineer to design the piping system to sustain the same forces. Because isolated slabs are designed precisely because expansive soil movement is a 'known natural phenomenon' at the site, the plumbing engineer is required under the PEDH to either isolate the plumbing from those forces or provide an alternative engineering design with robust technical justification demonstrating the plumbing can function properly under the predicted soil movement. Non-isolated plumbing — buried plumbing or non-isolated void systems — does neither, and therefore does not meet the minimum standard of care established by the ASPE PEDH.

Was the standard of care for protecting plumbing from expansive soil created by the 2024 IPC?

No. The ASPE PEDH language establishing the obligation to protect plumbing from natural earth movement phenomena has existed for many years and predates the 2024 IPC. The 2024 IPC Section 305.8 explicitly codified this requirement to make enforcement easier for building officials — but the underlying professional standard of care was already established by the ASPE PEDH, the ASA A40.8 National Plumbing Code (1955), all published editions of the IPC and UPC requiring protection from undue strains and stresses, and the 2012 federal court ruling in BPLW v. United States. The 2024 IPC is a clarification of obligations that already existed, not the creation of a new one.

ASPE Plumbing Engineering Design Handbook

Q: What does the ASPE Plumbing Engineering Design Handbook say about designing plumbing for natural environmental conditions?

The ASPE Plumbing Engineering Design Handbook Volume 4, Chapter 6 states that within structures designed to handle extreme natural phenomena, the piping system itself must be hardened or conditioned. In zones of known natural phenomena — such as areas susceptible to earth movement — the plumbing engineer must design the piping and support systems to sustain the shocks, stresses, and loads inherent with those forces. The handbook further states that while a plumbing system may not be expected to survive complete destruction of the building's structure, it is expected to survive intact and working in any event where the building structure itself survives.

The ASPE Plumbing Engineering Design Handbook (PEDH) can be purchased from the American Society of Plumbing Enginers here:

https://aspe.org/publications-news/aspe-plumbing-engineering-design-handbooks/

As noted in the 2023 ASPE Tech Symposium Presentation titled, "Failures of Non-Isolated Plumbing in Expansive Soil":

ASPE Plumbing Engineering Design Handbook, Vol 4, Chapter 6, “Hanger and Support Conditions”, “Natural Environmental Conditions” states:

[Bold print and highlighting provided for clarity]

“The susceptibility of a piping system to natural conditions must be accounted for within the piping system and the accompanying hangers, supports, and anchors. The major effect of these natural environmental conditions is on the basic building structure.However,within structures designed to handle extreme natural phenomena, the piping system itself must be hardened or conditioned.Typical natural phenomena consist of seismic forces and sustained periods of high winds, including hurricanes and typhoons, which create major stresses and loads on a building’s structure. For instance, an extreme high-rise building can move 4 to 13 inches (102 to 304 mm) laterally in high winds.In zones of known natural phenomena, such as areas susceptible to earth movement, the plumbing engineer must design the piping and support systems to sustain the shocks, stresses, and loads inherent with and applied by these extreme forces. The engineer must refer to the applicable building codes to determine the seismic design category for any mandated piping system support requirements.While a plumbing system may not be expected to survive the complete destruction of a building's structure, it is expected to survive intact and working in the event that the building structure itself survives."

This language in the ASPE PEDH clearly communicates that, as a minimum standard of care, a mechanical engineer is expected to coordinate their work with a geotechnical engineer and structural engineer and accommodate “known natural phenomena” “such as earth movement” which includes expansive soil, for the “stresses, and loads inherent with and applied by these extreme forces”. It also indicates that, as a minimum standard of care, a mechanical engineer is expected to design for the same natural phenomena that a structure is designed for. Given that isolated slabs are designed by structrual engineers to isolate the slab so as to avoid expansive soil movement, it stands to reason that a mechanical engineer complying with the expectations of the ASPE PEDH would at a minimum either isolate the plumbing or have an alternative engineering design that provides a robust technical justification proving to a building official that the plumbing is capable of properly functioning in the predicted expansive soil movement conditions. The non-isolated plumbing practice does not comply with the minimum expectations defined by the ASPE PEDH. No, this section of the ASPE PEDH does not mention the word “expansive soil” as it does not mention “collapsible soils” or “frost heave” or “underconsolidated fill” or any other unique site condition that a geotechncial engineer may recognize in a soil report as a natural phenomenon for design professionals to accomodate in the design. However, that does not mean that one should read this text so narrowly to argue that a mechanical engineer should not design for any earth movement except seismic just because there is a sentence in this section referring to a plumbing code reference to seismic design of plumbing supports. The non-isolated plumbing practice does not meet the standard of care as established by the long standing text of the ASPE PEDH in addition to the many other sources cited in the APIB Examination of the Standard of Care in the Protection of Plumbing from Expansive Soil.