9.2 Roof Drains and Conductors

9.2 Roof Drains and Conductors

Storm Drainage Materials and Joints (IPC Section 1102)

Unlike sanitary drainage systems, storm drainage systems are subject to rapid, high-volume flow and temperature-induced physical movement. Therefore, materials must be selected carefully. IPC Table 1102.4 specifies approved materials for above-ground and underground storm drainage piping.

Approved Piping Materials:

• Above-Ground Storm Piping: ABS (DWV), Cast Iron, Copper (Types K, L, M, and DWV), Galvanized Steel, PVC (DWV), Polyethylene, Polypropylene, and Stainless Steel (304 or 316).
• Underground Storm Piping: ABS (DWV), Cast Iron, Concrete, Copper (Types K and L), PVC (DWV), Polyethylene, Polypropylene, and Stainless Steel.

[!IMPORTANT] Galvanized steel pipe is approved for above-ground storm piping but is prohibited for underground installation due to its susceptibility to corrosion when in contact with soil. Always refer to Table 1102.4 for storm piping, and do not confuse it with sanitary piping material lists (Table 702.1).

Joint and Connection Standards

Joints must be gas-tight and liquid-tight. They must be made using materials approved for the piping system:

• Cast Iron: Hub-and-spigot joints must be made with hot-poured lead or compression gaskets. Hubless joints must use approved elastomeric couplings with stainless steel bands.
• PVC and ABS: Joints must be solvent-cemented or threaded. Transition joints between PVC and ABS must use approved mechanical fittings or transition cements.
• Expansion Joints: Under IPC Section 1102.6, expansion joints or expansion loops must be installed in storm piping runs where thermal expansion and contraction could cause stress. This is critical for vertical conductors running through multi-story buildings, as the warm building and cold rain water create large temperature differentials.

---

Roof Drain Construction and Strainer Requirements (IPC Section 1105)

Roof drains must be specifically designed to prevent debris from entering the piping system while maintaining high-flow capacity. The code establishes clear structural rules for these drains:

1. Dome Strainers (IPC Section 1105.1)

Standard roof drains on flat roofs must be equipped with dome-type strainers.

• Height: The strainer must extend not less than 4 inches (102 mm) above the surface of the roof immediately adjacent to the drain.
• Open Area: The strainer must have a free inlet area of not less than 1.5 times (150%) the cross-sectional area of the leader or conductor to which it connects.
• Purpose: The dome shape ensures that even if leaves or debris accumulate around the base, water can still flow through the upper portion of the dome.

2. Flat-Surface Deck Drains (IPC Section 1105.2)

Where roofs are used for sun decks, parking decks, or similar pedestrian/vehicular traffic, dome strainers are a hazard and are prohibited. Instead, flat-surface type drains must be installed level with the deck.

• Open Area: Because flat drains are more easily blocked by debris and traffic, they must have a free inlet area of not less than 2.0 times (200%) the cross-sectional area of the leader or conductor.
• Installation: Must be recessed or installed flush to prevent ponding and safety hazards.

---

Controlled-Flow Roof Drainage Systems (IPC Section 1110)

In many municipal jurisdictions, discharging massive volumes of storm water into public sewers during a storm overloads the municipal system, causing combined sewer overflows (CSOs) or flooding. Controlled-flow roof drainage (also called regulated or flow-control drainage) is a design method that temporarily stores water on the roof and releases it at a metered, slow rate.

Controlled-Flow Sizing and Operational Rules:

1. Approval: Controlled-flow systems are only permitted where explicitly approved by the local code official.
2. Control Devices: Water flow is restricted by calibrated control devices, such as vertical weirs with slot openings or orifice plates installed inside the roof drains.
3. Ponding Limits: The maximum depth of water permitted to pond on the roof at the drain must not exceed 3 inches (76 mm), unless the roof structure is engineered for a greater load.
4. Structural Engineering: The roof structure must be specifically designed and engineered to support the maximum possible weight of the ponding water. Water weighs approximately 62.4 lbs/cu ft, so a 3-inch depth represents a load of 15.6 lbs/sq ft over the roof surface.
5. Secondary Drainage: A secondary overflow drainage system (or scuppers) must still be provided to prevent water from rising above the maximum designed structural height of the parapet or roof.

---

Protection of Conductors and Leaders (IPC Section 1101.5)

Vertical storm drainage piping is often exposed in parking garages, loading docks, and warehouse interiors, making it vulnerable to impact.

• Mechanical Damage: The code requires that conductors and leaders subject to mechanical damage must be protected.
• Protection Methods: Approved protection includes encasing the pipe in steel sleeves, installing heavy-duty metal column guards around the pipe, or routing the piping inside structural columns.
• Insulation: Storm drainage piping carrying cold rainwater through warm building interiors must be insulated to prevent condensation (sweating), which can damage drywall, ceilings, and electrical systems.