15.2 Waste Receptors, Hub Drains, and Standpipes

What a waste receptor is

A waste receptor is the open fixture that catches indirect waste: a floor sink, a floor drain, a hub drain or a standpipe. IPC 802.3 requires it to be trapped and vented and connected to the building drainage system. The receptor is directly connected; the break is upstream of it.

The general rules — IPC 802.4

For other than hub drains that receive only clear-water waste and standpipes, a removable strainer or basket shall cover the outlet of waste receptors. Waste receptors shall not be installed in concealed spaces. Waste receptors shall not be installed in plenums, crawl spaces, attics, interstitial spaces above ceilings and below floors. Ready access shall be provided to waste receptors.

Four requirements:

1. Removable strainer or basket over the outlet — exempted only for hub drains receiving only clear-water waste and for standpipes.
2. Never in concealed spaces.
3. Never in plenums, crawl spaces, attics, or interstitial spaces above ceilings or below floors.
4. Ready access required.

The prohibition list is longer than the general "concealed" rule because each named space is a place where a receptor might be technically visible but practically unmaintainable — and where an overflow would be discovered only by the damage it caused.

802.4.1 Size of receptors: a waste receptor shall be sized for the maximum discharge of all indirect waste pipes served by the receptor, and installed to prevent splashing or flooding. Splash from a floor sink receiving a 15 gpm dish machine discharge contaminates the surrounding floor.

Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(pp) adds an exception permitting a waste receptor in a crawl space where equipment is installed there, provided an approved backwater valve is installed. Rule 1.2(E)(1)(oo) deletes the last sentence of IPC 802.3.

Hub drains — IPC 802.4.2

A hub drain shall be in the form of a hub or a pipe extending not less than 1 inch above a water-impervious floor.

The 1-inch rise is what makes a hub drain a receptor rather than a hole in the floor: it keeps floor washdown water and debris from entering, and it gives the indirect waste pipe a flood level rim to measure the air gap from.

The strainer exemption applies only where the hub drain receives only clear-water waste. A hub drain receiving food-handling discharge needs a removable strainer like any other receptor.

Standpipes — IPC 802.4.3

Standpipes shall be individually trapped. Standpipes shall extend not less than 18 inches but not greater than 42 inches above the trap weir. Access shall be provided to standpipes and drains for rodding.

Three numbers, and both bounds are enforced:

Too short and the washing machine's pump surge overflows the top of the standpipe. Too tall and the head of water left standing in the standpipe after the pump stops can siphon the trap, or simply drains too slowly to keep up with the next discharge.

Relate this to IPC 1002.1, which caps the vertical distance from a fixture outlet to the trap weir at 24 inches but expressly states that "the height of a clothes washer standpipe above a trap shall conform to Section 802.4.3." The standpipe rule supersedes the general 24-inch limit.

From Table 709.1: a residential automatic clothes washer is 2 dfu with a 2-inch minimum trap; a commercial automatic clothes washer is 3 dfu with a 2-inch trap. Footnote g points to IPC 406.2 for sizing the fixture drain, branch drain and drainage stack for an automatic clothes washer standpipe.

802.4.3.1 Connection of a laundry tray to a standpipe

As an alternative for a laundry tray fixture connecting directly to a drainage system, a laundry tray waste line without a fixture trap shall connect to a standpipe for an automatic clothes washer drain. The standpipe shall extend not less than 30 inches above the weir of the standpipe trap and shall extend above the flood level rim of the laundry tray. The outlet of the laundry tray shall be not greater than 30 inches horizontal distance from the side of the standpipe.

Note the different minimum: a standpipe serving only a clothes washer is 18 inches minimum; a standpipe that also receives an untrapped laundry tray waste is 30 inches minimum, and must also rise above the laundry tray's flood level rim. The maximum remains 42 inches.

The laundry tray in this arrangement has no trap of its own — it is protected by the standpipe trap, which is why the standpipe must rise above the tray's rim.

Clothes washer discharge interceptor — IPC 1003.6

Clothes washers shall discharge through an interceptor provided with a wire basket or similar device, removable for cleaning, that prevents passage into the drainage system of solids 1/2 inch or larger in size, string, rags, buttons or other materials detrimental to the public sewage system.

Two exceptions:

1. Clothes washers in individual dwelling units.
2. A single clothes washer designed for use in individual dwelling units and installed in a location other than an individual dwelling unit — the residential-style washer in a small office break room.

So a commercial laundry needs the interceptor; a house does not; and a single residential machine in a non-dwelling location does not.

Sizing the receptor and its load

Worked receptor load

A floor sink receives:

• two refrigerated display case drains (clear-water waste),
• one commercial dishwashing machine discharging 10 gpm, and
• one prep sink at 2 dfu.

Because the receptor receives more than clear-water waste, 709.4.1's one-half dfu value does not apply. Use 709.4 — the sum of the connected fixtures:

• Dishwasher: 10 gpm x 2 = 20 dfu (709.3).
• Prep sink: 2 dfu.
• Refrigerated case drains: clear water, but they are part of a mixed-waste receptor; count conservatively at the Table 709.1 floor drain value or the calculated clear-water flow.
• Total: not less than 22 dfu, and never less than the Table 709.1 value for the receptor itself.

That load then flows into the drainage sizing tables of IPC 710.

Common receptor defects