12.3 Subsoil Drains, Sump Pumps & Secondary Emergency Overflows
Key Takeaways
- IPC Section 1111.1 requires subsoil drains to be open-jointed, horizontally split or perforated pipe conforming to Table 1102.5, not less than 4 inches in diameter, discharging to a trapped area drain, sump, dry well or approved location above ground, and a subsoil sump is not required to have either a gas-tight cover or a vent.
- IPC Section 1113.1.2 requires a storm sump pit not less than 18 inches in diameter and 24 inches deep, and Section 1113.1.4 requires a gate valve and a full flow check valve on the discharge piping, with an exception permitting only a check valve in one- and two-family dwellings.
- 675 IAC 16-1.4-12(b) adds Section 1113.1.5, requiring water powered sump pumps to comply with Section 608 of the code.
- IPC Section 1107.3 sizes secondary roof drains per Section 1106 at the same rainfall rate as the primary system, requires scupper openings of not less than 4 inches, and directs that flow through the primary system not be considered when sizing the secondary system.
- 675 IAC 16-1.4-12(a) deletes IPC Section 1107.2 without substitution, so the model code's separate-systems requirement is not part of the Indiana Plumbing Code.
12.3 Subsoil Drains, Sump Pumps & Secondary Emergency Overflows
Core Principle: Managing storm and subsurface water requires two subsystems: foundation subsoil dewatering to protect the substructure, and secondary emergency roof drainage to prevent roof collapse. These are IPC Sections 1107, 1111, 1112 and 1113.
Read the code text closely in this section. Several widely taught "requirements" here — a 4-inch gravel bed, 12 inches of cover, geotextile wrap, a mandatory independent secondary piping system — are good construction practice or requirements of other codes, not provisions of the 2006 IPC. Indiana also deleted Section 1107.2 without substitution (675 IAC 16-1.4-12(a)), which removes the model code's separate-systems language from the Indiana Plumbing Code entirely. Where this section states a practice that the code does not mandate, it says so.
Subsoil Drains & Foundation Dewatering (IPC Section 1111)
Groundwater exerts immense hydrostatic pressure against below-grade foundation walls and basement floor slabs. In soils with high clay content—common throughout central and northern Indiana—rising water tables will penetrate masonry cold joints, cause slab heave, and flood interior subgrades unless relieved by a continuous subsoil drainage system.
SUBSOIL FOUNDATION DRAIN TRENCH
Basement Foundation Wall
|
| Earth / Native Soil
| |
| v
+=============+==============================+
| | |
| | Geotextile Filter Fabric |
| | +------------------------+ |
| Basement | | Washed Crushed Stone | |
| Floor Slab | | (Min. 12" over pipe) | |
| | | +------+ | |
+-------------+ | | (::) | <------+--+-- Perforated Subsoil Pipe
| Footing | | +------+ | | (Holes downward)
| | | Min. 4" Gravel Bed | |
+=============+ +------------------------+ |
+============================================+
What Section 1111.1 Requires
Section 1111.1 is short, and everything in it is testable:
"Subsoil drains shall be open-jointed, horizontally split or perforated pipe conforming to one of the standards listed in Table 1102.5. Such drains shall be not less than 4 inches (102 mm) in diameter. Where the building is subject to backwater, the subsoil drain shall be protected by an accessibly located backwater valve. Subsoil drains shall discharge to a trapped area drain, sump, dry well or approved location above ground. The subsoil sump shall not be required to have either a gas-tight cover or a vent. The sump and pumping system shall comply with Section 1113.1."
- Approved Pipe Materials (Table 1102.5): asbestos-cement (ASTM C 508); cast iron (ASTM A 74, ASTM A 888, CISPI 301); polyethylene (ASTM F 405, CSA B182.1, B182.6, B182.8); PVC sewer pipe PS25, PS50 or PS100 (ASTM D 2729, ASTM F 891, CSA B182.2, B182.4); Type 316L stainless steel drainage (ASME A112.3.1); and vitrified clay (ASTM C 4, ASTM C 700).
- The gas-tight-cover sentence is the exam point. A sanitary sewage sump under Section 712.3.2 must have a gas-tight removable cover and must be vented per Chapter 9. A subsoil sump under 1111.1 need not have either. Candidates who carry the sanitary rule across to the subsoil sump get this wrong.
Good Practice the Code Does Not Mandate
The following are standard construction details and are what an inspector expects to see, but they are not stated in Section 1111.1. Do not cite the section for them:
- Gravel Envelope: bedding the pipe on 4 inches of washed gravel or crushed stone (No. 8 or No. 57 aggregate) and covering it to about 12 inches above the crown.
- Geotextile Filtration: wrapping the aggregate envelope in filter fabric so fines cannot migrate in and blind the perforations.
- Perforation Orientation: turning the holes downward so groundwater rises into the invert and surface silt does not drop straight in.
- Elevation: setting the invert below the bottom of the basement floor slab, around the footing perimeter or beneath the slab.
Indiana Addition: Water Powered Sump Pumps (Section 1113.1.5)
675 IAC 16-1.4-12(b) adds Section 1113.1.5: "Water powered sump pumps. Water powered sump pumps shall comply with Section 608 of this code." A water-powered backup pump draws potable water to create the ejector's motive force, so Indiana routes it straight into the cross-connection control section — in practice a reduced pressure principle assembly or other Section 608 protection on the potable supply to the pump.
Sump Pits, Automatic Pumps & Discharge Piping (IPC Sections 1112 & 1113)
Where subsoil groundwater cannot drain to daylight or an outfall by gravity, it must discharge into an approved mechanical sump pit.
SUMP DISCHARGE PIPING ASSEMBLY
To Approved Storm Sewer / Splash Block
^
|
+----------------+----------------+
| FULLWAY SHUTOFF VALVE |
| (Ball Valve / Gate Valve) |
+----------------+----------------+
| UNION DISCONNECT |
+----------------+----------------+
| CHECK VALVE |
| (Prevents water backflow) |
+----------------+----------------+
| |
| 1/8" Relief Weep Hole |
| (Prevents pump air lock) |
Basement Floor | |
=====================+=================================+===
| | |
| v Discharge Pipe (Min. 1-1/4") |
| +------------+ |
| Inflow | | WATERTIGHT BASIN |
| -------> | SUMP PUMP | Min. 18" Diameter |
| | (Submers) | Min. 24" Depth |
| +------------+ |
+======================================================+
Basin Construction Criteria (IPC Section 1112.1)
- Minimum Dimensions: A sump pit must have a minimum diameter of 18 inches (457 mm) and a minimum depth of 24 inches (610 mm).
- Material Quality: Basins must be watertight, constructed of non-corrosive, non-decaying materials: rotational molded polyethylene, structural fiberglass, vitrified clay, or poured concrete.
- Basin Cover: Every pit must be provided with a rigid, fitted structural cover capable of supporting anticipated floor loads. While storm sump covers are not required to be gas-tight like sanitary ejector basins, sealing them prevents radon gas infiltration from underlying bedrock.
Pump Mechanism & Discharge Piping (IPC Section 1113)
- Automatic Actuation: Sump pumps must be equipped with an automatic float switch (vertical reed switch, tethered mechanical float, or electronic pressure switch) to cycle the pump automatically based on basin water elevation.
- Discharge Pipe Sizing: The discharge line must not be smaller than the pump manufacturer's discharge outlet, and in no case less than 1-1/4 inches (32 mm) inside diameter (1-1/2 inches is the standard commercial/residential practice).
- Mandatory Check Valve: A full-flow swing check valve must be installed in the vertical discharge line directly above the basin cover. This prevents the tall column of water remaining in the riser pipe from cascading back into the pit when the pump shuts off, which would cause short-cycling.
- Anti-Air-Lock Weep Hole: A 1/8-inch (3.2 mm) relief hole must be drilled into the discharge pipe between the pump discharge throat and the check valve. This relieves trapped air pockets that would otherwise air-lock the centrifugal impeller.
- Fullway Shutoff Valve: A fullway isolation valve (ball valve or gate valve) must be installed downstream of the check valve. This allows maintenance personnel to isolate the discharge main and service or replace the pump and check valve without draining the header.
- Union Disconnect: A mechanical union or quick-disconnect coupling must be installed between the pump and the shutoff valve for rapid pump extraction.
Prohibited Discharge Destination
Under IPC Section 1101.3, sump pumps discharging groundwater, subsoil drainage, or roof runoff are STRICTLY FORBIDDEN from connecting to the sanitary drainage system.
Connecting a sump pump to a basement laundry sink, floor drain, or sanitary stack is a serious code violation. During torrential rains, millions of gallons of clear sump discharge surge into municipal wastewater treatment plants, washing out biological digestion beds and forcing raw sewage to back up into residential basements.
Approved discharge points include:
- Dedicated public storm sewer.
- Rain garden, bioswale, or engineered drywell.
- Exterior concrete splash block directing water overland at least 5 feet away from building foundation walls.
Secondary (Emergency) Roof Drainage Systems (IPC Section 1107)
Flat commercial roofs enclosed by perimeter parapet walls present an extreme structural hazard. If autumnal leaves, nesting birds, windblown debris, or ice dams blind the primary roof drains, storm precipitation quickly turns the roof into a structural reservoir.
PRIMARY & SECONDARY OVERFLOW DRAINAGE
Parapet Wall Parapet Wall
+-----------+ +-----------+
| | | +---+ | <-- Overflow
| | | | | | Scupper
| | WATER ACCUMULATION DEPTH | +---+ | (Min. 2" above
| |==========================================|===========| primary drain)
| | | |
| +-----+ +-----+ |
| | | |
| | +-------+ +-------+ |
| | | DOME | | DOME | |
| | +---+---+ +---+---+ |
+-----+---| | |----------------------| | |-----------------+
+---+---+ +---+---+ Roof Deck
| |
v v
Primary Drain Secondary Drain
(To Storm Sewer) (Elevated 2" Inlet Ring;
Discharges Visibly Above Grade)
Mandatory Secondary Requirement (IPC Section 1107.1)
Secondary (emergency) roof drainage is mandatory on all roofs where water will be impounded if the primary drainage system clogs. Secondary systems must be sized to handle 100% of the design rainfall rate, assuming the primary system is completely inoperative.
Plumbing contractors may utilize either of two code-approved methods:
Method 1: Parapet Wall Overflow Scuppers (IPC Section 1107.3)
- Scupper Dimensions: Open scupper chutes through exterior parapet walls must have a minimum vertical opening height of 4 inches (102 mm).
- Elevation Above Primary Drain: The invert (bottom edge) of the scupper opening must be set at least 2 inches (51 mm) above the low point of the adjacent roof surface / primary drain strainer.
- Discharge Clearance: Scuppers must discharge freely into the atmosphere, dropping clear of the exterior facade.
Method 2: Separate Secondary Drainage Piping — and the Indiana Deletion
Where scuppers cannot be installed through parapets (long-span roofs, interior valley drains), designers install an independent secondary piping system. Understand exactly what the code does and does not say about it:
- The model 2006 IPC Section 1107.2 ("Separate Systems Required") is the provision that mandates independence. 675 IAC 16-1.4-12(a) deletes Section 1107.2 without substitution, so the Indiana Plumbing Code jumps from 1107.1 to 1107.3. Do not cite 1107.2 on an Indiana exam.
- What survives in Indiana is 1107.1 and 1107.3. Section 1107.1 requires secondary (emergency) roof drains or scuppers "where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason." Section 1107.3 requires secondary systems to be sized in accordance with Section 1106 based on the rainfall rate for which the primary system is sized in Tables 1106.2, 1106.3 and 1106.6; requires scuppers to be sized so ponding depth does not exceed what the roof was designed for under Section 1101.7; sets a minimum scupper opening dimension of 4 inches; and states that the flow through the primary system shall not be considered when sizing the secondary roof drain system.
- Elevated Strainers: setting secondary inlets roughly 2 inches above the primary is standard design practice so the secondary only runs when the primary has failed. It is a design convention here, not an IPC 2006 dimension.
- Visible Discharge Alarm: daylighting the secondary discharge above grade where occupants will see it is the whole point of an emergency overflow and is standard practice; in the 2006 IPC as adopted in Indiana it is not a separately codified sentence, so answer it as practice unless the stem supplies a local ordinance.
- Section 1101.7 (Roof Design) is the structural anchor: roofs are designed for the maximum possible depth of ponded water determined by deck and overflow levels in combination with deflected structural elements, assuming all primary roof drainage means are blocked.
Controlled-Flow Roof Drainage (IPC Section 1110)
In dense urban centers where municipal storm mains lack capacity to handle peak runoff, engineers utilize controlled-flow roof drainage:
+-------------------------------------------------------------------------+
| CONTROLLED-FLOW SIZING & ENGINEERING RULES |
+-------------------------------------------------------------------------+
| Design Parameter | Engineering Limit (IPC Section 1110) |
+------------------------+------------------------------------------------+
| Flow Regulation Device | Calibrated vertical weir rings or notched |
| | orifice rings fitted over drain inlets. |
+------------------------+------------------------------------------------+
| Structural Load Rating | Roof deck must be engineered to support the |
| | full calculated water depth (dead load). |
+------------------------+------------------------------------------------+
| Maximum Drain Time | Water must evacuate completely within 24 hours |
| | following cessation of the storm. |
+------------------------+------------------------------------------------+
| Maximum Water Depth | Controlled water depth cannot exceed 3 inches |
| | for flat roofs, or 6 inches for sloped decks. |
+------------------------+------------------------------------------------+
| Mandatory Backup | An independent secondary overflow scupper or |
| | secondary drain system is strictly required. |
+-------------------------------------------------------------------------+
Controlled-flow systems deliberately throttle stormwater discharge, using the structural roof deck as a temporary detention basin. Because standing water introduces severe dead loads (5.2 lbs/sq ft per inch), controlled-flow systems require registered professional engineering calculations and cannot be altered or modified in the field by plumbing installers.
Under IPC Sections 1113.1.2 and 1113.1.4, what pit dimensions and discharge valves are required for a storm sump?
Which statement about secondary (emergency) roof drainage is correct under the Indiana Plumbing Code?
What does IPC Section 1111.1 actually require for a subsoil drain?