3.3 Lavatories, Showers, Bathtubs & Scald Prevention (ASSE 1016/1017)

Sinks, Showers, Bathtubs & Water Safety

Bathing fixtures and handwashing lavatories represent the intersection of drainage hydraulics, structural waterproofing, and thermal safety engineering. Improperly installed shower pans cause catastrophic rot and structural mold within subfloors, while uncalibrated shower valves expose building occupants to severe thermal shock and third-degree scald burns.

For the Indiana Journeyman Plumber exam, candidates must master the dimensional mandates of IPC Chapter 4, understand multi-piece shower clamping drains, know the precise physical thresholds for shower enclosures, and thoroughly understand scald prevention standards under ASSE 1016, ASSE 1017, and ASSE 1070.

---

Lavatory Rough-Ins and Installation Standards

Lavatories (handwashing basins) must be installed with dedicated water supplies, drainage connections, and overflow channels:

• Drain Sizing: The minimum size of a lavatory fixture drain and P-trap is 1-1/4 inches in diameter. However, standard commercial and residential rough-in practice frequently transitions to a 1-1/2 inch horizontal fixture branch in the wall.
• Supply Rough-In: Lavatory supplies are roughed in with 1/2-inch nominal hot and cold copper or PEX tubing, terminating in angle stops with 3/8-inch O.D. compression riser tubes connected to the faucet shank. Hot water must connect to the left side; cold water must connect to the right side.
• Overflow Openings: Where lavatories are manufactured with overflow openings, the overflow must discharge into the inlet side of the P-trap or directly into the fixture drain tailpiece above the liquid trap seal (IPC Section 407.2). Removable pop-up drain assemblies or grid strainers must be installed to prevent debris from fouling the trap.
• Public Lavatory Water Temperature Limits: Under IPC Section 416.5, hot water delivered to public handwashing lavatories must be tempered to a maximum temperature between 85°F (29°C) and 110°F (43°C) by a temperature-limiting device conforming to ASSE 1070.

---

Shower Compartment Sizing & Dimensions (IPC Section 417.4)

The International Plumbing Code enforces strict dimensional minimums for constructed or prefabricated shower compartments:

1. Minimum Cross-Sectional Area

• Shower compartments must have a minimum finished interior cross-sectional area of not less than 900 square inches (0.58 m²).

2. The 30-Inch Minimum Dimension (and the 25-Inch Exception)

The 2006 IPC does not use the "encompass a 30-inch circle" language that appears in the UPC and in later IPC editions. Section 417.4 says a shower compartment "shall not be less than 30 inches (762 mm) in minimum dimension measured from the finished interior dimension of the compartment, exclusive of fixture valves, showerheads, soap dishes, and safety grab bars or rails."

• The area and the minimum dimension are measured from the finished interior dimension at a height equal to the top of the threshold, at a point tangent to its centerline, and that clearance continues to a height not less than 70 inches (1,778 mm) above the shower drain outlet.
• Exception (memorize this trade-off): a compartment with not less than 25 inches (635 mm) in minimum dimension is permitted provided the compartment has at least 1,300 square inches of cross-sectional area. Narrower means bigger.
• Accessible compartments are measured "except as required in Section 404" — and Indiana deleted Section 404 in favor of Chapter 29 of the Indiana Building Code.
• Section 417.4.1 adds the wall-finish rule: smooth, noncorrosive, nonabsorbent waterproof wall material to 6 feet above the room floor, and not less than 70 inches measured from the compartment floor at the drain.

3. Shower Lining and Threshold (IPC Section 417.5.2)

Section 417.5.2 is a liner section, and its numbers are about the liner, not about a curb height. Where a site-built shower floor is used (prefabricated receptors excepted), the floor must be lined and made watertight, and:

• The liner must turn up on all sides at least 2 inches (51 mm) above the finished threshold level.
• The liner must be recessed and fastened to an approved backing so it does not occupy the space required for the wall covering, and must not be nailed or perforated at any point less than 1 inch (25 mm) above the finished threshold.
• The liner must be pitched 1/4 unit vertical in 12 units horizontal (2-percent slope) toward the fixture drain and sealed watertight to the waste outlet at the seepage entrance.
• Section 417.3 sets the shower waste outlet at not less than 1-1/2 inches (38 mm) in diameter with a removable strainer not less than 3 inches (76 mm) in diameter and strainer openings not less than 0.25 inch.
• Barrier-Free / Curbless Showers: accessible and curbless configurations are governed by the building code and ICC A117.1, not by 417.5.2. Do not quote a curb height out of the plumbing code.

          SHOWER COMPARTMENT CLEARANCES & THRESHOLD

          |<------- 30" Diameter Circle Clear ------->|
          |                                           |
     ^    |                                           |
     |    |                                           |
    70"   |                                           |
    Above |                                           |
    Drain |                                           |
     |    |                                           |
     v    +-------------------------------------------+
          |                     |                     | Finished Threshold
          |                     |                     | Liner turns up
          |      Liner Slope    |                     | 2" min above it
          |   1/4" per Ft Min   v                     +-------+
          +---------------> ( DRAIN ) <---------------+       |
                                                              +--- Finished Floor

---

Shower Pan Liners & Sub-Drain Waterproofing

Built-in, on-site fabricated shower receptors (tile showers) must incorporate a continuous waterproof pan liner under IPC Section 417.5.2:

• Approved Materials: Sheet PVC (ASTM D4551, minimum 40 mil thickness), chlorinated polyethylene (CPE sheet - ASTM D4068, minimum 40 mil), sheet lead (not less than 4 lbs/sq ft), or sheet copper (not less than 12 oz/sq ft).
• Subfloor Pre-Slope: The wood subfloor or concrete base beneath the pan liner must be pitched toward the sub-drain weep holes with a uniform slope of not less than 1/4 inch per foot (2% slope). Installing a pan liner flat on a level subfloor violates code because trapped moisture will stagnate rather than drain.
• Turn-Up Height: Section 417.5.2 requires the liner to turn up on all sides at least 2 inches (51 mm) above the finished threshold level, and it may not be nailed or perforated at any point less than 1 inch (25 mm) above the finished threshold. Many manufacturers specify a taller turn-up; follow the greater of the two.
• Clamping Ring Sub-Drain & Weep Holes: Tile showers require a specialized three-piece shower drain. The pan liner is clamped between the drain base and the clamping ring, sealed with approved sealant. The clamping ring features weep holes that permit subsurface water penetrating the tile grout to enter the drain. Plumbers must place pea gravel, tile spacers, or dedicated weep hole guards around the weep holes prior to applying the mortar bed to prevent wet mortar from clogging the passages.
• Water Testing — know the source: the 2006 IPC has no shower liner test section. Section 312 runs only from 312.1 through 312.9, and 312.9 is the inspection and testing of backflow prevention assemblies (the subsection Indiana amended). A shower-pan flood test — plug the drain, fill to the top of the threshold, hold and inspect for a drop — is standard trade practice and is commonly required by the code official and by the liner manufacturer's instructions, which Indiana Section 101.4 makes binding. Later IPC editions added the test as code text; the 2006 edition did not.

---

Bathtub Overflows and Waste Fittings

Bathtubs must be provided with a waste outlet and an overflow fitting (IPC Section 406.1):

• Drain Sizing: Bathtub waste outlets must connect to a minimum 1-1/2 inch drain, P-trap, and overflow assembly.
• Slip Joints: Where slip-joint connections are used on the bathtub waste and overflow piping, they must be located on the inlet side of the trap and must remain accessible. An access panel measuring not less than 12 inches by 12 inches (305 mm x 305 mm) must be provided in the adjoining wall or floor. If the waste and overflow fitting is solvent-welded (glued PVC/ABS) or threaded brass, an access panel is not required.

---

Scald Prevention Standards: ASSE 1016 vs. ASSE 1017

Water temperature control in bathing fixtures is life-safety plumbing. Hot water at 140°F (60°C) produces third-degree scald burns in less than 5 seconds. At 130°F (54°C), a severe burn occurs in roughly 30 seconds. At 120°F (49°C), it takes more than 5 minutes of continuous exposure to cause a serious scald.

Point-of-Use Shower Valves (ASSE 1016 / ASME A112.18.1 / IPC 424.3)

Under IPC Section 424.3, all shower and combination tub/shower valves must be equipped with temperature-actuated mixing valves conforming to ASSE 1016 / ASME A112.18.1. Standard two-handle mixing valves that lack automatic scald protection are strictly prohibited in showers.

ASSE 1016 defines three distinct valve types:

1. Type P (Pressure-Balancing): Senses dynamic changes in incoming hot and cold water pressure. If someone flushes a water closet downstream, causing cold water pressure to plummet, a sliding piston or balancing spool instantly throttles the hot water port proportionally to prevent scalding.
2. Type T (Thermostatic): Senses water temperature directly using a wax capsule or bimetallic coil. The valve dynamically adjusts flow to maintain the set temperature regardless of supply temperature or pressure swings.
3. Type T/P (Combination): Combines both pressure-balancing and thermostatic mechanisms, delivering the highest degree of user protection against both pressure shocks and temperature creep.

[!IMPORTANT] The 120°F Maximum Limit & Field Calibration: IPC Section 424.3 explicitly mandates that the valve must be equipped with a high-limit rotational temperature stop that is field-adjusted by the installing plumber at the time of installation to limit the maximum delivered water temperature to 120°F (49°C). Plumbers must use an accurate thermometer in the flowing stream to verify and lock the stop.

Master Mixing Valves (ASSE 1017) vs. Point-of-Use (ASSE 1016 & ASSE 1070)

A frequent trap on the licensing examination is confusing source valves with fixture valves:

• ASSE 1017 (Master Thermostatic Mixing Valve): Installed at the hot water source (water heater or boiler supply loop). It allows water to be stored in the water heater at 140°F (60°C) to kill deadly Legionella pneumophila bacteria, while blending cold water at the tank outlet to distribute water through the building mains at 120°F to 125°F.
• Crucial Code Distinction: An ASSE 1017 master mixing valve does not substitute for ASSE 1016 shower valves. Section 424.3 requires the balanced-pressure, thermostatic, or combination valve to be installed at the point of use, and expressly states that in-line thermostatic valves shall not be utilized for compliance with this section. Downstream pressure fluctuations in long branch lines still cause thermal shock, so the point-of-use valve stays mandatory at every shower even with a master valve at the heater.
• ASSE 1070 (Water Temperature Limiting Devices): Section 416.5 requires tempered water to be delivered from public hand-washing facilities through an approved ASSE 1070 limiting device. Indiana added an exception at 675 IAC 16-1.4-5(i): "An ASSE 1070 point of use device may be omitted if the fixture is supplied with tempered water through an ASSE 1017 master mixing valve." 675 IAC 16-1.4-7(h) adds the identical exception to Section 607.1. That Indiana exception applies only to public hand-washing facilities — it does not relieve the Section 424.3 requirement for an ASSE 1016 valve at every shower.
• Section 424.4 (Multiple/gang showers): gang showers on a single tempered supply must be controlled by an approved ASSE 1069 or CSA B125 automatic temperature control mixing valve, or each head must have its own ASSE 1016 valve; either way the maximum setting is limited to 120°F (49°C).