13.3 Conductors, Leaders, Building Storm Drains & Sump Systems

13.3 Conductors, Leaders, Building Storm Drains & Sump Systems

Exam Focus: Storm drainage networks encompass more than roof basins and scuppers; they comprise an interconnected mechanical infrastructure of vertical stacks, underground building drains, subsoil footing collection systems, and engineered sump pumps. On the Michigan Journeyman Plumber licensing examination, questions frequently test code terminology (conductors vs. leaders vs. storm drains), approved piping materials under MPC Section 1102, subsoil drainage construction, sump pit dimensions and pump head calculations under MPC Section 1113, the strict statutory ban on Inflow and Infiltration (I&I) under Michigan Department of Environment, Great Lakes, and Energy (EGLE) regulations, and the operational criteria for controlled flow roof drainage under MPC Section 1110.

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1. Statutory Definitions & Storm Drainage Terminology (MPC Chapter 2)

Precision of language is mandatory in plumbing code compliance. Candidates must differentiate the three primary conduits that convey storm water:

+-----------------------------------------------------------------------------+
|                   STORM DRAINAGE SYSTEM TERMINOLOGY                         |
+-----------------------------------------------------------------------------+
|                                                                             |
|  [1] CONDUCTOR (Interior Vertical):                                         |
|      - A vertical pipe installed INSIDE the building envelope that conveys  |
|        storm water from the roof drain down to the horizontal storm drain.  |
|                                                                             |
|  [2] LEADER (Exterior Vertical):                                            |
|      - An exterior vertical downspout pipe installed on the OUTSIDE of the  |
|        building facade that conveys storm water from eaves, gutters, or     |
|        collector boxes down to the ground or storm drain.                   |
|                                                                             |
|  [3] BUILDING STORM DRAIN (Horizontal Interior):                            |
|      - Horizontal piping installed INSIDE or beneath the building slab that |
|        receives discharge from conductors, subsoil drains, or area drains   |
|        and extends to 3 to 5 FEET outside the building wall.                |
|                                                                             |
|  [4] BUILDING STORM SEWER (Horizontal Exterior):                            |
|      - The exterior continuation of the building storm drain beginning      |
|        30 inches beyond the exterior wall outside the building foundation wall and extending to    |
|        the public storm sewer or approved point of disposal.                |
+-----------------------------------------------------------------------------+

                      COMPLETE STORM DRAINAGE NETWORK

         ROOF DRAIN (Primary)
             |  |
             |  |  <--- ROOF DRAIN BODY & CLAMPING RING
       +-----+  +-----+
       |              |
       |  CONDUCTOR   | (Interior Vertical Pipe)
       |  (Insulated) | 
       |              |
       +-----+  +-----+
             |  |
             |  |=======================\   <--- BASE OF STACK LONG SWEEP
             |                           \
             |   BUILDING STORM DRAIN     \ (Horizontal Inside Building)
             +=============================+====================+  (Foundation Wall)
                                           |                    |         |
                                           |  EXTERIOR CLEANOUT |         |
                                           |         |          |         |
       SUBSOIL FOOTING DRAIN               |         v          | 3 to 5' |
       (Perforated Pipe in Gravel)         +---------|----------+---------+
                   |                                 |                    |
                   v                                 |  BUILDING STORM    |
            [SUMP BASIN]                             |      SEWER         |
            [ & PUMP   ]============================>+===================>| TO PUBLIC
            (Check Valve & Union)                                           STORM SEWER

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2. Approved Materials & Condensation Insulation (MPC Section 1102)

Under MPC Table 1102.4 (Building Storm Drain Piping) and Table 1102.5 (Subsoil Drain Piping), all piping materials installed within buildings must meet rigid structural and temperature ratings:

+-----------------------------------------------------------------------------+
|                  APPROVED STORM DRAINAGE MATERIALS                          |
+-----------------------+-----------------------------------------------------+
| Application           | Approved Material Standards                         |
+-----------------------+-----------------------------------------------------+
| Interior Conductors   | - Cast Iron (Hubless: ASTM A888/CISPI 301;          |
| & Building Storm      |   Hub-and-Spigot: ASTM A74)                         |
| Drain (Above & Below  | - PVC Plastic Pipe Schedule 40 DWV (ASTM D2665)     |
| Slab)                 | - ABS Plastic Pipe Schedule 40 DWV (ASTM D2661)     |
|                       | - Galvanized Steel Pipe (ASTM A53)                  |
|                       | - Copper Tube (Type DWV, M, L, or K; ASTM B88/B306) |
|                       | - Ductile Iron (AWWA C151)                          |
+-----------------------+-----------------------------------------------------+
| Subsoil Footing       | - Perforated PVC (ASTM D2729)                       |
| Drains (Underground)  | - Perforated Corrugated Polyethylene (ASTM F405)    |
|                       | - Perforated ABS (ASTM D2751)                       |
|                       | - Porous Concrete Pipe (ASTM C654)                  |
+-----------------------+-----------------------------------------------------+

The Problem of Conductor Condensation ("Sweating")

Rainwater entering a roof drain during cold spring or autumn cloudbursts in Michigan typically has a temperature of 35°F to 45°F (1.7°C to 7.2°C). When this freezing water cascades down an interior metal or plastic conductor traversing a heated plenum space (72°F with 50% relative humidity), the exterior surface of the pipe drops below the dew point.

Water vapor in the surrounding air rapidly condenses onto the outside of the pipe, forming heavy liquid beads that run down and soak acoustic ceiling tiles, destroy electrical equipment, and foster toxic mold growth. In commercial Michigan practice, all horizontal and vertical interior conductors must be thermally insulated with fiberglass or elastomeric closed-cell foam insulation equipped with a continuous vapor barrier jacket.

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3. Subsoil Footing Drainage Systems (MPC Section 1111)

Michigan's climate and clay-heavy glacial till soil retain immense amounts of groundwater. Under MPC Section 1111, subsoil drains must be installed around the perimeter of all buildings featuring basements, crawlspaces, or earth-retaining foundation walls.

                      PERIMETER FOOTING DRAIN ANATOMY

                EARTH BACKFILL
                      |
                      v
           +---------------------+  
           |                     |  <--- GEOTEXTILE FILTER FABRIC SOCK
           |   +-------------+   |       (Prevents silt/clay intrusion)
           |   | WASHED ROCK |   |
           |   | (3/8"-3/4") |   |  <--- WASHED CRUSHED GRAVEL (Min 12" over pipe)
           |   +-------------+   |
           |   | (O) (O) (O) |   |  <--- PERFORATED PIPE (Holes pointed DOWNWARD!)
           |   +-------------+   |
           |   | WASHED ROCK |   |  <--- BEDDING GRAVEL (Min 4" under pipe)
           +---+-------------+---+
           =======================  <--- CONCRETE FOUNDATION FOOTING

Installation Best Practices

1. Location: Placed outside the foundation footing, with the invert of the pipe sitting below the level of the interior basement concrete slab.
2. Bedding & Envelope: Bedded on not less than 4 inches of washed gravel or crushed stone (3/8" to 3/4" diameter) and covered with not less than 12 inches of crushed stone envelope.
3. Filter Fabric Membrane: The stone envelope and perforated pipe must be wrapped in a geotextile filter fabric to prevent fine silt and clay from choking the interstitial voids in the gravel bed.
4. Orientation of Perforations: Perforations in rigid drainage pipe must face DOWNWARD (at the 4 o'clock and 8 o'clock positions). If holes face upward, water cannot enter until the water table submerges the entire pipe, and descending surface silt falls directly into the pipe, creating chronic sedimentation.

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4. Sump Pump Systems & Hydraulic Head Sizing (MPC Section 1113)

Where subsoil groundwater or storm drainage cannot be discharged by gravity, it must discharge into an approved sump pit and be lifted to the storm drainage network by an automatic sump pump.

Dimensional Mandates (MPC Section 1113.1.1)

• Sump Pit Dimensions: Under MPC Section 1113.1.1, a storm/subsoil sump pit must have a diameter of not less than 18 inches (457 mm) and a depth of not less than 24 inches (610 mm).
• Construction Material: Concrete, precast polyolefin plastic, fiberglass, or coated steel, resting on a solid, level gravel bedding.
• Airtight Covers: While open grates are permissible for external storm basins, any sump pit located inside a habitable residential dwelling, basement, or commercial facility must be fitted with a gasketed, airtight gas-tight cover to prevent the infiltration of radon gas and damp soil odors.

Valving & Discharge Pipe Rules (MPC Section 1113.1.1 & 1113.1.3)

• Discharge Pipe Sizing: The discharge pipe diameter must match the pump outlet, but can never be less than 1-1/4 inches (32 mm) nominal size (standard commercial practice mandates 1-1/2 inches).
• Check Valve Mandatory: A full-flow check valve (swing check or spring-assisted check) must be installed in the vertical discharge line directly above the sump cover. The check valve prevents the heavy column of water standing in the vertical pipe from back-draining into the basin when the pump shuts off, which would cause short-cycling.
• Union / Isolation Valve: A pipe union and a full-flow gate or ball valve must be installed downstream of the check valve to permit rapid pump removal and servicing without draining the overhead line.

+-----------------------------------------------------------------------------+
|                  SUMP PUMP HEAD LOSS & CAPACITY SIZING                      |
+-----------------------------------------------------------------------------+
|                                                                             |
|  TOTAL DYNAMIC HEAD (TDH) = STATIC HEAD + FRICTION HEAD LOSS                |
|                                                                             |
|  [1] STATIC HEAD:                                                           |
|      - Vertical distance from the bottom of the sump pit to the highest     |
|        point of the discharge piping elevation.                             |
|                                                                             |
|  [2] FRICTION HEAD LOSS:                                                    |
|      - Resistance generated by water moving through straight pipe, elbows,  |
|        tees, and valves, converted into equivalent feet of pipe.            |
|                                                                             |
|  [3] PUMP SIZING CURVE:                                                     |
|      - Plumber must select a pump capable of delivering the required        |
|        gallons per minute (GPM) AT the calculated Total Dynamic Head.       |
+-----------------------------------------------------------------------------+

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5. Environmental Prohibition: Storm-to-Sanitary Cross-Connections

A paramount environmental life-safety standard enforced across Michigan is the absolute statutory ban on introducing storm drainage or subsoil groundwater into the municipal sanitary sewer.

The Engineering Pathology of Inflow & Infiltration (I&I)

Under MPC Section 1101.3 and administrative rules enforced by the Michigan Department of Environment, Great Lakes, and Energy (EGLE) under the Natural Resources and Environmental Protection Act (NREPA, Act 451 of 1994, Part 31 - Water Resources Protection):

"Storm water, surface water, groundwater, roof runoff, subsoil drainage, and noncontact cooling water shall not be discharged into a municipal sanitary sewer."

1. The Massive Flow Disparity: A single 4-inch roof drain during a 2.75 in/hr storm in Detroit discharges 70 to 80 GPM ($4,500\text{ gallons per hour}$). By contrast, a standard modern water closet discharges only 1.28 gallons per flush. Connecting just two commercial downspouts to a sanitary line introduces the hydraulic equivalent of a residential subdivision flushing water closets simultaneously.
2. Sanitary Sewer Overflows (SSOs): Sanitary sewers and municipal wastewater treatment plants (WWTPs) are biological systems engineered for domestic sewage. When storms introduce millions of gallons of rainwater (Inflow and Infiltration), collection mains surcharge, blowing manhole covers off and flooding neighborhood basements with raw human waste. Overloaded WWTPs are forced to open emergency bypass gates, discharging hundreds of millions of gallons of untreated, pathogenic raw sewage into Lake Michigan, Lake Huron, the Detroit River, and inland waterways.
3. Penalties: Illegal storm connections expose the owner and the installer to enforcement by EGLE under Part 31 of NREPA. MCL 324.3115(1) directs the court to impose a civil fine of not less than $2,500, with a maximum of not more than $25,000 per day of violation, in addition to injunctive relief and mandatory disconnection orders.

Legacy Combined Sewers and MPC Section 1101.3

MPC 1101.3 is one sentence: "Storm water shall not be drained into sewers intended for sewage only." There is no numbered exception beneath it - the rule turns entirely on what the municipal sewer was intended for. In older historic urban cores (such as legacy sectors of Detroit and Saginaw), the municipal infrastructure contains combined sewers engineered to receive both sewage and stormwater in a single deep underground brick or concrete tunnel. A legally permitted combined sewer is not a sewer "intended for sewage only," so connecting storm water to it does not violate 1101.3. In these explicitly designated districts:

• Storm connections are permitted ONLY with specific written approval from the code official and the sewer owner; MPC 1101.2 still requires storm water to drain to an approved place of disposal.
• The building storm drain must connect to the combined sewer through an approved storm trap (running trap) fitted with an accessible cleanout and a fresh air inlet to prevent toxic sewer gases from venting out through roof drains or sidewalk grates.

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6. Controlled Flow Roof Drainage Systems (MPC Section 1110)

In densely developed commercial zones, municipal storm sewers cannot handle the immediate peak runoff generated by acres of impervious roof surfaces. Rather than requiring developers to construct massive underground concrete retention vaults on expensive real estate, MPC Section 1110 permits the installation of Controlled Flow Roof Drainage Systems.

+-----------------------------------------------------------------------------+
|              CONTROLLED FLOW ROOF DRAINAGE (MPC SECTION 1110)               |
+-----------------------------------------------------------------------------+
|                                                                             |
|  [1] OPERATING PRINCIPLE:                                                   |
|      - Roof drains are fitted with calibrated vertical weir rings, notched  |
|        collars, or internal flow-control orifices (e.g., 25-30 GPM/drain).   |
|      - Restricts discharge rate into storm sewers, temporarily detaining    |
|        stormwater atop the flat roof deck.                                  |
|                                                                             |
|  [2] STRUCTURAL LOAD ENGINEERING:                                           |
|      - The building structural frame and roof deck must be specifically     |
|        engineered by a licensed structural engineer to support the maximum  |
|        designed ponded water load (dead load + live load).                  |
|                                                                             |
|  [3] MANDATORY 24-HOUR DRAIN-DOWN TIME (MPC 1110.1):                        |
|      - The drainage design must ensure that the detained water drains down  |
|        COMPLETELY within not more than 24 HOURS after precipitation stops.  |
|                                                                             |
|  [4] DUAL DRAIN MINIMUM (MPC 1110.2):                                       |
|      - Not less than TWO roof drains must be installed in each separate     |
|        roof catchment area to prevent single-point obstruction.             |
|                                                                             |
|  [5] EMERGENCY OVERFLOW PROTECTION STILL MANDATORY:                         |
|      - Secondary overflow scuppers or secondary drains must remain active,  |
|        set above the designed detention water depth to prevent overload.    |
+-----------------------------------------------------------------------------+

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7. Realistic Exam Application Scenarios

Scenario A: Residential Sump Head Loss Calculation in Oakland County

Exam Scenario: A journeyman is installing a submersible sump pump in a residential basement in Troy, Michigan, to evacuate groundwater from perimeter footing drains. The vertical static lift from the bottom of the sump pit to the horizontal discharge pipe at the ceiling rim joist is 9 feet. The piping run consists of 30 feet of 1-1/2 inch Schedule 40 PVC pipe, two 90-degree elbows (each equivalent to 4 feet of pipe), and one full-flow swing check valve (equivalent to 11 feet of pipe). The footing drain inflow is estimated at 30 GPM.

What is the Total Dynamic Head (TDH) that the pump must overcome, assuming the pipe friction loss is 3.5 feet of head per 100 feet of pipe at 30 GPM?

Code Analysis & Calculation:

1. Calculate Total Equivalent Length of Pipe:
   • Straight pipe = $30\text{ feet}$
   • Two 90° elbows = $2 \times 4\text{ ft} = 8\text{ feet}$
   • One swing check valve = $11\text{ feet}$
   • Total Equivalent Length = $30 + 8 + 11 = 49\text{ feet}$
2. Calculate Friction Head Loss: $\text{Friction Loss} = \frac{49\text{ ft}}{100\text{ ft}} \times 3.5\text{ ft of head} = 1.715\text{ feet of head}$
3. Calculate Total Dynamic Head (TDH): $\text{TDH} = \text{Static Lift} + \text{Friction Loss} = 9.0\text{ ft} + 1.715\text{ ft} = 10.72\text{ feet (round to 11 ft)}$
4. Pump Selection Conclusion: The plumber must select a sump pump whose manufacturer performance curve delivers at least 30 GPM at 11 feet of Total Dynamic Head.

Scenario B: Illegal Footing Sump Discharge in Grand Rapids

Exam Scenario: During an inspection of a newly renovated commercial office building in Grand Rapids, the plumbing inspector observes that the 1-1/2 inch PVC discharge line from an interior subsoil groundwater sump pump is connected directly into a 4-inch sanitary soil stack in the mechanical room. When questioned, the contractor claims that since groundwater is clean, it will help flush the sanitary line.

What code violations exist, what regulatory agency has jurisdiction, and what is the required remedy?

Code Analysis:

1. Severe Code Violation (MPC Section 1101.3): Clear-water waste, rainwater, and subsoil groundwater are strictly prohibited from discharging into the sanitary drainage system. This connection constitutes illegal Inflow and Infiltration (I&I).
2. Environmental Violation: Violates Michigan EGLE administrative rules under NREPA Act 451 Part 31. Groundwater overloads the municipal sewage treatment plant and creates acute risks of sanitary sewer overflows.
3. Required Correction: The contractor must disconnect the sump pump from the sanitary soil stack. The discharge must be re-piped to an approved building storm drain, an exterior storm sewer, or discharged by gravity onto grade via an approved splash block directed away from the building foundation.