2.2 Horizontal Branch Drains, Pitch & Changes in Direction

What counts as a horizontal branch

A horizontal branch drain collects fixture drains and carries them to a stack or a building drain. It is not a building drain, building subdrain, building sewer or private interceptor main sewer. Those are sized with Table 382.30-3 and are covered in section 2.4. Footnote b of Table 382.30-2 says this directly: the "drain piping other than stacks" column does not include building drains, subdrains, sewers or forced discharge piping.

Sizing horizontal branches with Table 382.30-2

Three points come up repeatedly:

• A 2-inch branch holds 6 dfu. Seven dfu needs a 3-inch branch.
• A 3-inch branch holds 20 dfu, and the jump to 4 inches allows 160.
• The values are maximums "through any portion" of the pipe, so check the most heavily loaded segment, usually just upstream of where the branch joins the stack.

Minimum trap sizes still come from Table 382.30-1: a lavatory trap is 1-1/4 inches and a shower trap 2 inches. A branch sized from the dfu total alone must still accept those trap outlets.

Minimum pitch (SPS 382.30 (5))

Worked example. A 40-foot run of 3-inch horizontal branch at the minimum 1/8 inch per foot drops 40 x 0.125 = 5 inches. The same length of 2-inch branch at 1/4 inch per foot drops 10 inches. That drop often decides whether the branch can reach the stack above a basement ceiling.

Changes in direction (SPS 382.30 (8))

Changes in direction must use 45-degree wyes, long or short sweep quarter bends, or sixth, eighth or sixteenth bends (or equivalent combinations). For drain piping 8 inches or smaller, fittings must meet the minimum radii in Table 382.30-4:

Three exceptions relax the table for the first 90-degree fitting downstream of certain fixtures:

1. Lavatory or sink trap, 1-1/2 inch drain: 1-3/4 inch minimum radius, and the fitting must be a tee or quarter bend.
2. Water closet on 3-inch drain: 2-1/2 inch minimum radius.
3. Water closet on 4-inch drain: 3-inch minimum radius.

Where blowout-type fixtures are installed back to back, fittings must keep waste from passing from one fixture into the other (SPS 382.30 (8) (b)).

Fittings and connections (SPS 382.30 (9))

Fittings may not retard flow more than normal friction. Specific rulings:

• A 4 x 3 inch closet bend or collar reduction is not an obstruction.
• The side inlet of a low- or high-pattern tee or bend may not be used as a vent connection when the side inlet is horizontal.
• Prohibited for drain piping: a heel inlet bend with the heel inlet horizontal, any fitting with an enlargement chamber or a ledge or shoulder, a reduction in area in the direction of flow, running threads, and connections made by drilling and tapping (unless the department approves).
• Pipe saddles must meet SPS 384.30 (5) (d).

Drain piping over food and pool areas (SPS 382.30 (13))

Where drain piping runs below the ceiling of a space where food, ice or potable liquids are prepared, handled, stored or displayed:

1. Floor penetrations need sleeves bonded to the floor that protrude at least 1 inch above the finished floor, with the annular space sealed.
2. Fixtures above, except bathtubs and showers, must be wall-mounted; bathtub waste-and-overflow connections must be made above the floor.
3. Floor and shower drains above need integral seepage pans.
4. Cleanouts must extend through the floor above.
5. Piping that can sweat must be insulated.

The ceiling must be removable or have access panels. Exposed drain piping may not be located over a pool, surge tank or open pool filter unless a trough diverts seepage to an approved discharge point.