Updated Guidance for Food Service Plumbing
We have updated a guidance document about plumbing requirements in food service establishments. The guidance includes:
- The types of fixtures required to discharge to a grease interceptor,
- Direct versus indirect plumbing connection requirements, and
- Similar plumbing design considerations for food service establishments.
In the future, we will extend this guidance to include kitchen appliance backflow requirements and other similar details.
Grease Interceptors and Pollution Control Units
We have had several recent projects with Pollution Control Units (PCU), so we’re taking this opportunity to review existing PCU requirements. These requirements were established in coordination with Seattle Public Utilities’ Fats, Oils, and Grease (FOG) program and are meant to protect the public drainage system.
Any time a PCU is installed with piped drainage connections, the drain lines from the PCU must discharge to an approved indirect receptor and that receptor must discharge to an approved grease interceptor. The grease interceptor serving the PCU drains must be separate and independent from the primary kitchen grease interceptor. The primary grease interceptor cannot be used because the surfactants applied to a PCU are strong enough to dislodge captured grease from the primary interceptor and wash it downstream where it will later reharden in the sewer system.
If the PCU includes an automated water wash cycle, a sampling port is required downstream of the PCU interceptor to manage potential future FOG discharge violations. If the PCU is connected to a fire protection system water supply and only includes drainage to accommodate fire protection functionality internal to the unit and incidental cleaning, a sampling port is not required.
All PCU installations with piped drainage connections will also require plumbing plan review. For now, this is covered under the “Unusual or uncommon processes or system configurations” provision of our Occupancy and Use guidance document, but a more explicit citation will be added in a future update to help alleviate any confusion.
Practical Application of Energy Code C404.2.1 Exception 1
Ever since the 2021 Washington State Energy Code became effective on March 15, 2024, there have been questions surrounding how Exception 1 to section C404.2.1 would be applied. In the 2018 Seattle Energy Code, there was a similar exception for electric resistance service water heating, but it was based on a maximum allowable wattage per permit. The new language provides a wattage limit per building (text of exception below):
 Applying this exception is not an issue for single tenant buildings, but becomes quite difficult to administer for multi-tenant buildings. The local building official does not have the capacity or staffing to survey and document the current tenants of every building to verify that some amount of electric resistance is still available to use the exception. After seeking guidance from multiple agencies, we were ultimately directed by Seattle Department of Construction and Inspections (SDCI) to apply Exception #1 of C404.2.1 to multi-tenant buildings as follows:
- 24KW plus 0.1 wats per square foot of building area of electric resistance service water heating capacity is allowed per building. Where a building includes multiple tenants, the 24KW allowance shall be prorated according to the percentage of the total conditioned floor area occupied by each tenant.
This means if you have a 5,000sf tenant space in a 50,000sf building, your specific tenant would be allowed to use 2.4KW (10% of building floor space = 10% of the initial 24KW) plus 0.1watts/sf of the tenant space (5,000 x 0.1 = 500 watts or 0.5KW) for a total of 2.9KW of electric resistance storage water heating for that tenant space. This is how the exception will be applied in our jurisdiction unless there is a code revision or updated direction from SDCI.
By Dave Price, Assistant Chief Plumbing Inspector, Public Health - Seattle & King County
One of the most consequential updates to the 2021 Seattle Plumbing Code was a rewrite of section 1018 which covers parking garage drainage systems. The revision was meant to be a compromise between standard industry practice from code cycles past and a very strict interpretation that would not allow anything that was not a parking garage drain to connect to the parking garage drainage system.
Why connect to a parking drainage system?
Typically, it is a matter of keeping things simple and not duplicating infrastructure. For example, if mechanical condensate discharges to a building sanitary system, it’s much more economical to install a simple non-trapped and non-vented indirect receptor connected to the garage drainage system using the required sand interceptor or oil/water separator as a trap seal rather than install a separate dedicated sanitary branch.
Creating exceptions
To make the intended compromise work, clear rules and boundaries needed to be established. The introduction to the Section 1018.2 exceptions make it clear that the primary baseline is still to only allow garage drains to discharge to the garage drainage system. The five exceptions listed also fall under a general statement of “Where first approved by the Authority Having Jurisdiction…” to denote that each exception is subject to prior approval. It is also noted that fixtures connected upstream of the sand interceptor or oil/water separator are not required to be individually trapped or vented. The fixtures are protected from sewer gas through the trap seal of the interceptor. To ensure the trap seal remains in place, the interceptor must be served by an electronic trap primer.
Another requirement noted in the exception statement is that all drainage piping downstream of drains connected to the parking garage drainage system, including the interceptor, must be sized for the largest flow of influent anticipated from any single drain under emergency or worst case conditions. This means that if you discharge an elevator hoistway drain with a volume of 50 gallons per minute (GPM) to the garage drainage system, the piping downstream of the receptor and the interceptor itself must also be capable of handling a flow rate of 50 GPM. If you discharge a reduced pressure backflow assembly relief line with a published flow rate of 230 GPM into the garage drainage system, then the downstream piping and interceptor need to be able to accommodate that flow rate. If both loads were connected to the same parking garage drainage system, the system would only need to accommodate the largest of the two possible emergency flow rates (230 GPM).
The five exceptions in Section 1018.2 provide flexibility
The first two exceptions are fairly self-explanatory, but the remaining exceptions can be somewhat hard to understand. Exceptions 3 and 4 are very similar: each is intended to allow an elevator hoistway drain to discharge to the garage drainage system. The main difference is Exception 3 addresses situations where the garage drainage system drains to the public sewer by gravity, while Exception 4 covers situations where the garage drainage system is routed to a lift station. Ejector pumps are not permitted to be connected to Emergency Power. Therefore, it would be possible for the hoistway pump (which is on Emergency Power) to be running and the lift station pumps that serve that drain to not be running. Unless the hoistway is somehow protected from flooding, the hoistway pump could simply be recirculating the same water (mixed with anything else that was in the lift station sump) back into the hoistway pit. The simplest way to provide that protection is to ensure the flood level of the lift station is at a lower elevation than the floor level of the lowest elevator lobby.
Exception 5 is relatively simple, but the intent can be difficult to understand. While using the oil/water separator or sand interceptor as a trap for the entire garage drainage system prevents sewer gas from entering the building, it does not prevent odors, gases, or fumes from passing between interconnected drains. Because there are no traps or vents on individual drains, there is nothing to prevent the passing of air between them. These drains may be in different rooms or different parts of the building. The requirement for each individual room with fixtures draining to the garage drainage system to open directly into the parking garage and to be continuously exhausted or provided with a permanent opening is to avoid circumventing fire separation requirements and keep a remote mechanical room from inadvertently being filled with noxious gas through an open connection to the garage drainage system.
Summary
Although these exceptions may seem difficult to comply with at times, they are ultimately intended to provide flexibility to the designer or engineer. Remember, the default as stated in 1018.2 is: “Drainage from any plumbing fixture other than a parking garage floor drain shall not be interconnected with the parking garage drainage system.” Hopefully exceptions 1-5 provide the flexibility intended while also providing some reasonable guardrails.
If you have ideas for how to improve these code sections in the next code cycle, please feel free to send a note to: planreviewinfo@kingcounty.gov.
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