The following is a link to the Geoprofessional Business Association (GBA) recommendations related to protection of plumbing from expansive soil.  The Mudskipper System meets these recommendations.  The Pipe Void System by SuperVoid and the PlumbingVoid System by VoidForm do not meet these recommendations.  


Below is the text from the GBA website related to this topic.  In the last paragraph below, the underlined text has been added to clarify which products do and do not meet the recommendations.  For clarification, the underlined text in the last paragraph is not on the GBA website. 



Nov 29, 2021 | News

GBA Geotechnical Business Committee

New language in the 2024 International Plumbing Code (IPC) will explicitly mandate how under-slab plumbing is to be protected from expansive soil, reducing professional liability risk for geotechnical engineers. Rather than wait for local building codes to adopt the 2024 IPC (which will take several years), the Geoprofessional Business Association (GBA) recommends that member-firms address this issue now for project sites with expansive soils and start referencing the new 2024 IPC language now in their geotechnical reports. Details of the code change and GBA’s recommendations are provided below.

Background for Code Change

Geotechnical engineers occasionally get tangled up in litigation related to leaky plumbing. While plumbing design and construction are not within the geotechnical scope of work, when expansive soils are present at a site the geotechnical engineer will need to address potential problems with foundations, floor slabs, and other structures. Water from leaking plumbing can cause expansive clay soils to swell much more than anticipated.

That increased swelling can compound the issue by making leaks even worse, potentially leading to failure of the plumbing and/or structural damage to a building. This damage can be greater, and more expensive to repair, when the floor slab is isolated from expansive soil but the plumbing is not. When these plumbing failures occur, the resulting litigation is often unfairly targeted at the geotechnical engineer of record by association due to the role of expansive soils.

IPC Code Change

To reduce the risk of plumbing failures and resulting litigation, changes in the next edition of the IPC have been made that prohibit the use of plumbing that is directly or indirectly in contact with soil in the active zone below floor slabs that are isolated from expansive soil (e.g., slabs that are over a crawlspace or voidforms). In these cases, the plumbing below the structure must be entirely isolated from contact with the soil. Prior to this code change, plumbing that is only partially isolated (i.e., proprietary products are used to create indirect contact between the plumbing and the expansive soil) has been allowed by building officials. However, there are concerns about those products failing because they do not actually isolate the plumbing from expansive soil movement. The full text of the new code requirements is provided below.

These improvements to the IPC were proposed by the Structural Engineers Association of Texas (SEAoT). SEAoT also submitted to the IPC a 14-page rationale statement for the change which was based on a review of the state of the art, recent litigation, a publication from the Foundation Performance Association, and various products on the market. SEAoT’s proposal was supported by GBA, the American Institute of Architects, the American Council of Engineering Companies – Texas, and several individual engineers from various design disciplines. A representative of GBA testified during the International Code Council’s hearings on these changes earlier this year. GBA’s te was provided by Steve Wendland, PE, PG, DGE, a member of the GBA Board of Directors, who summarized the litigation experiences of GBA member firms that had dealt with this problem.

Reduce Your Risk – Take Action Now

New editions of codes are typically not put in force by local governments until a few years after their publication, but GBA member firms can act now to reduce their risk as the standard of care changes. Rather than waiting years for these new plumbing code provisions to be enacted by the local government, GBA recommends that member firms act now for project sites with expansive soils. Taking this action now will also be beneficial for projects where the Uniform Plumbing Code (UPC) is in force; the UPC will not be making similar changes. For geotechnical reports on projects with expansive soils where the floor slab will be above a crawlspace or void forms, GBA recommends that the reports include recommendations that are consistent with this new section of the 2024 IPC, regardless of whether the IPC or the UPC is locally adopted. Specifically, the following (or similar) text could be used in a geotechnical report:

• The expansive soils at this site will undergo shrink and swell with changes in moisture content. This soil movement can damage plumbing below the structure, especially where it connects to or penetrates the structure. Damaged plumbing will leak, causing significantly more swelling of the soils, leading to possible failures of the plumbing or structural damage to the building. The project mechanical engineer should account for this concern in their designs.

• Where slabs are isolated from expansive soils by an under-floor voidspace, such as with a crawlspace or a space created by voidforms, under-slab plumbing should be suspended so that plumbing, hangers, and supports are isolated from the expansive soil by a voidspace. The void space should be a minimum of [insert dimension] inches vertically clear above the subgrade and a minimum of [insert dimension] inches horizontally clear between the subgrade and any plumbing, hangers, or supports. To protect and maintain the voidspace, soil below it should be sloped or benched on a minimum of [insert number] units horizontally for every 1 unit vertically, or structurally retained in accordance with an approved design methodology that accounts for lateral expansion of expansive soil.

• It should 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. As a clarifying exception to this recommendation, it is acceptable for plumbing to be suspended by a deep foundation system. These recommendations for isolation of plumbing can be met by installing anchors and plumbing within a crawlspace after an isolated slab is installed. It should not be permitted for a slab and plumbing to be lifted off the subgrade as an assembly to create the voidspace unless the under-floor space is a crawlspace with access to allow inspection of plumbing after lifting. At each location where a plumbing line transitions to a buried condition beyond the perimeter of the foundation, an adequately flexible expansion joint should be provided in the plumbing system to accommodate the effects of expansive soil swelling and shrinking. The flexible expansion joint should also be isolated from soil and accessible for maintenance. These recommendations for isolation of plumbing do not apply to the portions of a plumbing system that provide drainage of an under-floor space.

•      Several proprietary or patented systems are available on the market which are intended to isolate plumbing from expansive soil subgrades. However, many of these systems, such as the Pipe Void System by SuperVoid and the PlumbingVoid System by VoidForm, do not meet these recommendations. The project mechanical engineer should only use plumbing isolation systems on this project that are compliant with these recommendations, such as the Mudskipper System.