9.3 Subsoil Drainage and Sump Pumps

9.3 Subsoil Drainage and Sump Pumps

Subsoil Drainage Systems (IPC Section 1111)

Subsoil drainage systems, commonly known as foundation or perimeter drains, are installed around the crawl space or basement footings of a building. Their primary purpose is to collect groundwater and prevent hydrostatic pressure from building up against foundation walls and slabs, which can cause structural damage and water infiltration.

Materials and Standards (Table 1102.5)

Piping materials used for subsoil drains must be perforated or open-jointed to allow groundwater to enter. Approved materials include perforated PVC, perforated polyethylene (PE), perforated clay, and perforated concrete.

Installation Requirements (IPC Section 1111.1)

Proper installation is critical to prevent soil from entering the pipe and clogging the system over time.

1. Bedding and Backfill: The pipe must be laid in a bed of gravel, slag, crushed stone, or other approved filter material.
2. Gravel Thickness: The gravel must extend at least 2 inches (51 mm) below the bottom of the pipe and at least 4 inches (102 mm) on the sides and top of the pipe.
3. Filter Membrane: The gravel envelope must be covered with an approved geotextile filter fabric. This fabric allows water to pass through but blocks silt and sand, preventing the gravel and pipe perforations from clogging.
4. Slope: While subsoil drains are typically installed level around footings, they must drain by gravity or discharge into an approved sump pit.

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Sump Pits and Receivers (IPC Section 1113)

When subsoil drainage cannot flow by gravity to a storm sewer or natural drainage outlet, it must discharge into an approved sump pit where it is pumped out.

Sump Pit Dimensions (IPC Section 1113.1.4)

The physical dimensions of a sump pit are regulated to ensure proper pump operation and longevity:

• Minimum Diameter: Sump pits must not be less than 18 inches (457 mm) in diameter.
• Minimum Depth: Sump pits must not be less than 24 inches (610 mm) deep.
• Purpose: A pit that is too small will cause the pump to start and stop too frequently—a condition called short-cycling. Short-cycling quickly overheats and destroys the electric motor. The minimum 18" x 24" size ensures there is adequate water storage volume to allow the pump to run for a reasonable duration.

Sump Covers

Sump pits must be provided with a secure cover.

• For storm water and subsoil sumps, the cover must be solid and capable of supporting pedestrian traffic.
• Unlike sanitary sump pits (which collect sewage), storm sump pits do not require a gas-tight, airtight cover or a vent pipe, unless they receive sanitary waste or are located in an area where radon mitigation is required.

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Sump Pump Sizing and Valve Requirements (IPC Section 1113)

Sump pumps must be sized to handle the calculated design flow rate of the incoming water.

Valve Sequence (IPC Section 1113.1.3)

To ensure the pump operates safely and can be serviced, the discharge piping must contain specific valves in a precise order:

1. Check Valve: A check valve must be installed on the discharge pipe. The check valve prevents water in the vertical lift pipe from flowing back down into the sump pit when the pump turns off. Without a check valve, the pump would have to re-pump the same water repeatedly, leading to short-cycling and premature failure.
2. Full-Port Shutoff Valve: A full-port shutoff valve (such as a ball valve or gate valve) must be installed on the discharge pipe on the discharge side of the check valve (downstream of the check valve). This allows a technician to close the valve and remove the pump or check valve for maintenance without having all the water in the discharge line drain out.
3. Valve Connection Order: Sump pit → Pump → Check Valve → Shutoff Valve → Discharge Outlet.

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Approved Places of Disposal and Separation (IPC Section 1104)

A fundamental rule of modern plumbing engineering and code enforcement is the absolute separation of storm water and sanitary sewage.

[!CAUTION] IPC Section 1104.1 states that storm water, subsoil water, and sump pump discharges must never be connected to or discharged into the building's sanitary drainage system.

Rationale for Separation:

• Overloading Treatment Plants: Sump pumps and foundation drains pump relatively clean groundwater. If routed to the sanitary sewer, they overload municipal wastewater treatment facilities, leading to sewage backups during heavy storms.
• Cost: Processing clean water at a sewage treatment plant is highly inefficient and expensive for municipalities.

Approved Disposal Locations:

Subsoil and storm water must discharge to:

1. An approved public storm sewer system.
2. A dry well or drainage field on the property.
3. A drainage ditch, swale, or other natural watercourse.
4. The ground surface, provided it discharges at a point that drains away from the building and does not cause a nuisance to adjacent properties.