This is the first in a multi-part series focused on architectural coordination as it relates to mechanical, electrical, plumbing, and fire protection systems, based on changes to the International Building Code for the 2021 code cycle. This article addresses a significant revision between the 2018 and 2021 International Plumbing Codes that could have a notable impact on architectural coordination with plumbing design—specifically regarding water service entry locations.
The referenced code reads as follows, with the critical text in bold:
Backflow preventers for water service entries typically consist of two isolation valves with two check valves in between. The space between the check valves can trap water and is equipped with a relief port to alleviate pressure. To control where this discharged water is directed, it is common to install an air gap fitting that routes the flow to a floor drain, floor sink, or trench drain.
The change in the code language significantly impacts the size of the drain required to support this assembly. Standard practice has been to provide a drain sized to handle a minor check valve hang-up or the intermittent drip from a failing seal. However, manufacturer-published data is based on a worst-case scenario—complete removal of the check assembly under full pressure—resulting in extremely high discharge rates. Consider this note from Watts:
As a result, the new code language, combined with manufacturer data, can require drains that exceed typical commercial sanitary connection sizes. In practical terms, the expected failure discharge rate from this device could necessitate increasing a 4″ sanitary connection to 6″ or 8″, or a 6″ connection up to 10″ for a combined domestic and fire service.
There are several strategies to address this challenge:
- Upsizing the main building drain
- Providing a separate building drain
- Using multiple smaller backflow devices
- Locating the backflow device above grade, with an air gap draining to grade
Upsizing the main or providing a separate building drain both lead to higher sanitary piping costs, larger site piping, and potentially increased utility connection fees. We view these options as a last resort.
Using multiple, smaller backflow preventers is often more cost-effective than increasing the building drain size, though it is not without drawbacks. This approach involves duplicating expensive equipment, increasing spatial requirements, and adding maintenance complexity.
Installing the backflow preventer above grade level is likely the least costly option, but comes with its own challenges. Water services are typically routed to the building façade facing the main street—often the architectural focal point. A visible, protruding pipe at this location may not align with design goals. Additionally, a significant discharge or even a slow leak can create nuisance or safety issues. In northern climates, this could lead to hazardous icing conditions.
On the positive side, above-grade installations require no drain upsizing, consume minimal floor area, and offer immediate visual detection of malfunctions—potentially allowing for quicker repairs.
Whichever solution fits your project best, it’s clear that moving water service connection planning earlier in the programming and space planning process is a smart design move.
If you’d like to see how Barton can support the planning phase of your project, give us a call or send an email. For questions about this or other technical topics, please reach out to Barton’s Director of Mechanical Engineering, Stephen E. Oskin, PE, LEED AP at 814-231-2180 or seo@ba-inc.com with questions about any items covered in this article.