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Home / Code Guides / Sump Pits & Pumps

Sump Pump Code Requirements — Pit Size, Discharge & Wiring

A sump pump is the last line of defense for a below-grade floor, and the code cares about four things: the pit, the pump, where the water goes, and how the pump is powered.

RequirementModel Code StandardSection
When a sump is requiredFoundation drains around basements and below-grade walls must drain by gravity to daylight or to an approved drainage system — where gravity is not available, the drain discharges into a sump pit and is pumped outIRC R405.1, R405.2.3
Pit sizeThe pit has to hold enough water that the pump is not short-cycling — the code floor is 18 in. in diameter and 24 in. deep, built of an approved durable material such as plastic, tile, or concreteIRC R405.2.3, P3303
Pump capacity and dischargeThe pump must be capable of discharging not less than 15 gpm through a discharge pipe of at least 1-1/2 in.IRC R405.2.3, P3303
CoverThe pit gets a removable cover strong enough for the loads over it — and a gasketed, sealed cover is what you want anywhere radon or humidity matters, since an open pit is a direct path from the soil into the basementIRC R405.2.3; Appendix F
Check valveA check valve on the vertical discharge keeps the standing column of water from draining back into the pit each cycle — the IRC does not spell it out for foundation sumps, but pump manufacturers and most local amendments require oneManufacturer instructions per IRC R102.4; local amendment
Where it dischargesTo a storm sewer, drywell, or the ground surface far enough from the house that the water does not come straight back — never into the sanitary sewer, and not across a sidewalk or onto a neighbor’s lotIRC R405.2.3; local storm drainage ordinance
ElectricalReceptacles in unfinished basement areas require GFCI protection, and the old exception that let a dedicated sump receptacle skip it is gone from current codeIRC E3902.5

Worth knowing

  • The sump is one of the largest soil-gas entry points in a house. In a high-radon area a sealed lid with a grommeted cord penetration costs almost nothing during construction and is miserable to retrofit.
  • A passive radon stack can be tied to a sealed sump lid instead of a sub-slab stub, but the lid has to be genuinely airtight for that to accomplish anything (IRC Appendix F).
  • GFCI protection and sump reliability genuinely conflict — a nuisance trip during a storm floods the basement. The answer is an alarmed or monitored outlet plus a battery backup pump, not an unprotected receptacle.
  • Freeze protection matters as much as capacity: a discharge line that ices shut in January leaves the pump running against a closed pipe. Slope it, and keep the outdoor termination above grade and clear.
  • A sump taking only foundation drainage is a storm sump; a pit receiving any sanitary waste is a sewage ejector under an entirely different set of rules (IRC P3007).
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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