2.3 Bathtubs, Showers, Sinks & Food Prep Fixtures

2.3 Bathtubs, Showers, Sinks & Food Prep Fixtures

Bathing, showering, and culinary fixtures represent major water discharge points in both residential and commercial buildings. Because these fixtures directly involve human bodily immersion or food handling, code requirements strictly address anti-scald temperature control, watertight shower pan liners, structural access, and cross-connection prevention via indirect waste systems.

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Bathtubs & Combination Tub/Showers

Anti-Scald Protection (ASSE 1016 Compliance)

Water temperature control in bathtubs and combination tub/showers is governed by UPC Section 408.3. All tub/shower valves must be equipped with an anti-scald control valve conforming to ASSE 1016 / ASME A112.18.1 / CSA B125.1.

Approved valve types include:

1. Pressure-Balancing Valves: Senses changes in incoming hot and cold water supply pressures. If cold water pressure drops suddenly (e.g., someone flushes a nearby toilet), a sliding internal spool shifts immediately to reduce hot water flow, preventing thermal shock or scalding.
2. Thermostatic Mixing Valves: Senses water output temperature using an expanding wax element or bimetallic strip, modulating hot and cold water volume to maintain the set temperature regardless of supply line fluctuations.
3. Combination Pressure-Balance / Thermostatic Valves: Combines both pressure-sensing spools and temperature-sensing elements.

Maximum Temperature Setting: Anti-scald mixing valves must be equipped with a high-limit rotational stop, field-adjusted at the time of installation to cap maximum output temperature at 120°F (49°C).

Waste Outlets & Whirlpool Bathtubs

• Waste Sizing: Bathtubs must have a waste outlet and P-trap with a minimum diameter of 1-1/2 inches (40 mm).
• Whirlpool / Jetted Tubs (UPC 409.0): Circulation pumps on whirlpool bathtubs must be self-draining to prevent stagnant water retention in internal piping. An access panel measuring at least 12 x 12 inches (305 x 305 mm) must be provided to service the pump and motor. If the pump is located more than 2 feet from the access opening, the opening size must be increased to at least 18 x 18 inches (457 x 457 mm).

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Showers & Shower Pan Construction

Compartment & Curb Dimensions

• Minimum Interior Area: Finished shower compartments must have a minimum interior area of 1,024 square inches (0.66 m²).
• Minimum Clearance: The compartment must be capable of encompassing a 30-inch (762 mm) diameter circle measured from floor level up to a height of 70 inches above the drain.
• Curb / Threshold Height: The finished curb or threshold height must be a minimum of 2 inches (51 mm) and a maximum of 9 inches (229 mm) measured from the top of the drain outlet.

+---------------------------------------------------+
|                SHOWER ENCLOSURE                   |
|                                                   |
|                 /-------------\                   |
|                /               \                  |
|               |   30-Inch (D)   |                 |
|               |     Circle      |                 |
|                \               /                  |
|                 \-------------/                   |
|                                                   |
+-----------------------+---------------------------+
                        | <-- Threshold / Curb
                        v (Min. 2" to Max. 9" High)

Field-Fabricated Shower Pan Materials & Slope

Where custom tiled shower pans are constructed, subfloor waterproofing is critical. The subfloor below the pan liner must slope toward the weep holes of the subdrain at a pitch of 1/4 inch per foot (20.8 mm/m).

Approved Pan Lining Materials (UPC 408.7):

• Sheet Lead: Minimum weight of 4 lbs per sq ft (1/16" thick), coated with asphalt paint.
• Sheet Copper: Minimum weight of 12 oz per sq ft.
• PVC Flexible Sheet Liner: Minimum thickness of 40 mil (0.040 inch / 1.02 mm) conforming to ASTM D4551.
• CPE Flexible Sheet Liner: Minimum thickness of 40 mil conforming to ASTM D4068.
• Hot-Mop Asphalt: Minimum 3 plies of 15-lb felt saturated with 4 continuous coats of hot asphalt.

Subdrain & Hydrostatic Testing

Shower pans feature a two-piece subdrain equipped with clamping rings and weep holes. Weep holes permit moisture migrating through the tile mortar bed to enter the drain pipe. Weep holes must be protected with gravel or plastic weep-hole guards to prevent mortar blockage.

Hydrostatic Water Test: Before tile or mortar setting bed installation, the shower liner MUST be tested (UPC 408.7.5):

1. Insert an expandable test plug into the subdrain below the weep holes.
2. Fill the shower receptor with water to the top of the threshold or curb (minimum 2 inches deep).
3. Maintain water level for at least 15 minutes with zero measurable leakage or drop in water level.

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Sinks & Food Preparation Fixtures

Domestic Sinks

• Waste Sizing: Domestic kitchen sinks carry a 2 DFU rating, requiring a minimum 1-1/2 inch tailpiece and P-trap.
• Dishwasher Connection — read the Iowa amendment: Rule 481—425.4(6)"a" rewrites UPC Section 807.3 to read that no domestic dishwashing machine may be directly connected to a drainage system or food waste disposer "without the use of an approved dishwasher air gap fitting on the discharge side of the dishwashing machine, or by looping the discharge line of the dishwasher as high as possible near the flood level of the kitchen sink where the waste disposer is connected." In other words, Iowa accepts the high loop as an alternative to a countertop air gap fitting. Where an air gap fitting is used, it must be installed with its flood level (FL) marking at or above the flood level of the sink or drainboard, whichever is higher.

Commercial Food Preparation Sinks (Strict Indirect Waste Rule)

Commercial sinks used for washing, soaking, preparing, or processing food, vegetables, pots, or culinary ice CANNOT be directly connected to the sanitary drainage system (UPC Section 801.1).

• Hazard: Direct connection creates a severe health risk—if the sewer line backs up, raw sewage could flood directly into sinks containing food products.
• Mandatory Air Gap: Food preparation sinks must discharge indirectly into an approved indirect waste receptor (such as a floor sink or mop basin) through a physical Air Gap.
• Air Gap Dimension: The vertical distance through open air between the waste pipe outlet and the receptor flood level rim must be at least 2 times the diameter of the drain pipe, and never less than 1 inch (25 mm).

   Food Prep Sink Drain Pipe (1-1/2" Dia)
                   |
                   |  <-- Physical Air Gap
                   v  (Min. 2x Pipe Dia = 3 Inches)
     ============================= <-- Receptor Flood Rim
     |    Floor Sink Receptor    |
     +---------------------------+
                   |
                   v
         To Sanitary Drain System