What Is the Pitch for a Drain?

Basics

• Plumbing appliances such as sinks, bathtubs, shower stalls, washing machines and dishwashers deliver water at the turn of a valve. These devices also require a drain to dispose of the liquid. The surface or pipe on which the drain is located must slope in such a way as to draw water away from the home. The specifications for this slope or pitch are detailed in local and state building codes, which are based on the International Residential Code, or IRC, and the International Plumbing Code. The International Code Council, a nonprofit organization, maintains these and other construction regulations to ensure fixture durability, efficiency and safety of all plumbing systems.

Showers

• Because of their quantity, only a few of the IRC regulations are listed here. Shower floors must slope toward the drain at least 0.25 units for every 12 horizontal units, which is a 2-percent slope, but less than 0.5 units for every 12 units or 4 percent. The drain must have a flange that provides a watertight joint to the floor, so liquids run only into the drain. The walls and floor around a shower receptor must be lined with sheet lead, sheet copper, plastic liner material, hot mapping or sheet-applied waterproof membranes. This lining must slope at 0.25 in 12 units or 2 percent toward weep holes in the subdrain through a solidly formed subbase.

HVAC Systems

• Heating, ventilation and air-conditioning equipment requires a method of draining excess moisture. Condensation from cooling coils or evaporators of HVAC systems must go through a pipe with minimum horizontal pitch of 0.125 units in 12 units of horizontal movement, or a 1-percent slope. The pipe must slope in the direction of the approved place of disposal, which must not be a street or alley. If an overflow from the HVAC system can damage building components, a secondary drain or auxiliary drain pan is also needed with the same horizontal drain pipe pitch as the previously described initial drain pipe.

Building Drains

• The building drains carry discharged water from plumbing fixtures and appliances away from the home to the main sewer line. The number of fixture units that can connect to this drain or its branches depends on the diameter and slope of the pipe. For example, a 1.5-inch-diameter pipe sloping at 0.25 or 0.5 inches per foot can have only two waste fixtures, or only one when serving a garbage disposal discharge or a pumped discharge fixture. A 4-inch pipe sloping at 0.125 inches per foot can have 180 fixtures. At 0.25 inches of slope, it can have 216 fixtures, and at 0.5 inches of slope, it can have 250 fixtures.