Commercial restroom design considerations
By John A. Clark, P.E.
Restrooms available in public buildings, sport venues, offices, rest stops, theaters, etc. are considered “commercial.” The design considerations must address the number of users, durability, water savings, serviceability, initial and operational costs, and have Americans Disabilities Act (ADA) accessibility.
The design team needs to meet with the owners to define the economic quality of the fixtures used as, “good, better and best.” Then, the facility must be designed as per the current and local codes.
The typical toilet selected today uses 1.6 gallons per flush (gpf) rate. High-efficiency units are also available using a 1.28 gpf rate. Fixture manufactures have all designed their units to clean and remove the solids at the lower flush rates.
"Good” restrooms can use tank flush units. The tank flush mechanism can have a solid or liquid flush operator. A sign on the wall above the unit can define which device to push. The flush handle must be on the wide side of the ADA toilet stall.
“Better” restrooms can use an exposed flush valve control. A sign can also define to lift the lever up or down for a liquid or solid material flush. Sensor flush valves are also another choice; exposed or concealed for the “best” design.
The science of ergonomics has directed most toilets to have a “comfort/chair height” and elongated bowels. The mounting height also meets the requirements for ADA.
“Good” toilets are the floor mounted tank type units. These units are very durable and very stable for the obese segment of our population. Consider using an insulated tank in high humidity areas of the country. The insulated tank will avoid condensate drips below the tank.
“Better” fixtures are wall mounted units. Tank type or flush valve units are available in this group. This choice makes it easier to keep the toilet stall easier to clean. Install the unit with a three or four point floor mounted carrier to prevent the fixture from pulling away from the wall. Rear outlet floor set units are used in buildings constructed with precast or post tension slabs. However, be aware that a rear outlet fixture requires a higher water pressure of 35 psi for the flush valve. The flush valve selections are either a handle flush or a sensor flush.
The “best” fixture would be a wall mounted toilet with a concealed flush valve. The operations staff should set the sensitivity of the sensor flush to avoid any slight movement of the user to activate the flush.
ADA conditions that must be considered are to have the flush handle of the tank type toilet on the wide side of the stall. Also, the same consideration for a handle flush valve. If restrooms are constructed back to back for men and women, the flush units must be specified are two separate units to ensure the handles to be on the wide side of the stall. The mounting height of the flush valves must be coordinated with the mounting height of the grab bars in the ADA stalls.
The urinal fixture choices today are the low water use units. The 1 gpf and the one-pint per flush are the common selection. The use of water free units has declined due to that most local plumbing codes require water use fixtures. Water free units can be negotiated with the code official if water is installed to serve the fixtures if needed in the future. The choices for water free units are liquid seal type and memory rubber seal type. The seal cost and the maintenance cost should be compared to the water saving cost of using less water.
When urine is in contact with water, odor is generated. The use of odor control cakes should be considered in the maintenance costs. The water free units do not have an odor condition. Wash down urinals mix water with urine, resulting in residual urine odor. Siphon-jet urinals provide a clean flush and only leave pure water in the fixture bowl.
The target area of the fixture should be a design consideration. The ADA unit should have a target area high enough for the normal user. The small front lip fixture mounted at ADA height results in having urine on top of the fixture as well as on the floor in front of the fixture.
Mineral deposits tend to form in the waste line of banks of urinals, such as shopping malls and sports arenas. The mineral deposit builds up and eventually plugs the drain line. Provide a greater pitch in the urinal waste line and provide a cleanout to remove any mineral build up. Provide dividers between the fixtures to allow privacy.
Tempered water is the best choice for handwashing. The tempered water temperature should be in the 110°F - 115°F. range. Provide a tempering valve to control the mixing of 120°F water to arrive at the tempered water. Many restrooms today are using point of use electric water heaters under the sink counter to provide the tempered water to all nearby faucets.
Available supply faucet types are: hot and cold handles, single lever handles, sensors and push down controllers. If the goal of the restroom design is to be touchless, select the sensor type. Sensitivity of the faucet is important and the source of power is available from transformers, batteries, and turbogenerators. Any lever units for ADA requirements must of a longer length than the normal lever handle. The push down (30 seconds) units must be mineral-free and set for the average time to wash hands.
Most sink faucets are using the 0.5 gallons per minute (gpm) flow restrictor nozzle. If liquid soap is provided, it takes longer to remove the duds from the sinks. Research has also shown the refillable soap dispensers can become contaminated. The solution to both problems is to use a pod container foam soap dispenser. The sink should have a grid drain strainer and an overflow opening.
The faucet spouts should be the 5-inch type to avoid back splashing on the sink or counter. ADA spouts should also be the 5-inch gooseneck radius units. The wall mounted sinks are becoming more popular to achieve a public restroom to be handicap-friendly, easy to maintain, and clean/dry.
All restrooms have floor drain to carry away any water overflows from a toilet, sink or urinal. The simple solutions are to have the restroom cleaners add a little water to the drain at each cleaning. Other choices are to add mineral oil to the drain water to reduce evaporation, provide trap primers, or use memory rubber trap seals. The drain location should be under a stall partition to avoid any one from peeing into the drain if the restroom is very busy. The drain trap tends to go dry over time and sewer gas contributes to odor complaints.
Also, verify that the restroom is exhausting a minimum of 2 cfm per square foot. Often, the fan belt may have come off or be broken. A simple test is to hold a piece of toilet paper on the exhaust surface to see if the air flow can hold the paper tight to the grille.
Other design features
Hand dryers should also be touchless for either paper or electric hand drying. Electric hand dryers tend to be noisy, therefore, be aware if noise is objectionable in spaces, such as theaters, and then avoid this type of dryer for this venue. Consider wall protection to minimize any wall water stains under electric blow dryers. Verify the recommended mounting height for electric blow dryers between men’s and women’s restrooms. Also, check if there would be any conflict with any wainscoting tile up to a certain height under the dryer.
Review and select the toilet paper dispenser, the toilet seat cover dispenser, and a baby changing station. Provide water and water piping protection under the sinks for the handicapped user protection.
The entrance/exit path can be doorless, or a latchless door that swings outward with just a push. If the code requires the door to swing in, provide paper towels in the restroom and a trash container near the exit door. The paper towel can be used to grab the door opening handle. All trash containers should have open tops.
Restrooms constructed in new buildings should have the design team review with local code officials if the “Stevens Sizing Method” for drainage lines can be used to provider smaller waste lines and a greater drain pitch.
The design team should have discussions with the owner, owner’s maintenance staff, available contractors, and local code officials to define the Owner’s Project Requirements (OPR) for any certifications, cost or operational savings, and target visual goals. Settle on a level of “good, better and best” for the design, construction and operational goals.
John A. Clark, P.E., is a retired Senior Management MEP Engineer with over 50 years of experience with commercial, health care, and industrial projects. He has authored many articles and papers on plumbing, fire protection and HVAC.