IPC Storm Drainage Systems 2 — Questions and Answers
Question 1: Per the IPC, what is the minimum allowable size for a roof drain?
- 2 inches
- 3 inches (Correct answer)
- 4 inches
- The size must equal the conductor diameter
Correct answer: 3 inches
The IPC specifies that roof drains shall not be less than 3 inches in size, regardless of the calculated drainage area.
Question 2: Under the IPC, horizontal storm drainage piping larger than 3 inches in diameter must have a minimum slope of:
- 1/16 inch per foot
- 3/8 inch per foot
- 1/4 inch per foot
- 1/8 inch per foot (Correct answer)
Correct answer: 1/8 inch per foot
Horizontal storm drain pipes larger than 3 inches in diameter require a minimum slope of 1/8 inch per foot, less than the 1/4 inch required for smaller pipes.
Question 3: According to the IPC, are combined sanitary and storm drainage systems permitted in new construction?
- Yes, always permitted to reduce installation cost
- Yes, but only for one- and two-family dwellings
- No, except where specifically approved by the administrative authority (Correct answer)
- No, and no exceptions exist under any circumstances
Correct answer: No, except where specifically approved by the administrative authority
The IPC prohibits combined sanitary and storm drainage systems in new construction unless the administrative authority specifically approves it, such as where the public system is combined.
Question 4: Per the IPC, subsoil (foundation) drainage systems must discharge to:
- The sanitary building drain only
- The public sanitary sewer at all times
- An approved location such as a storm drain, combined sewer (where approved), or daylight (Correct answer)
- A sump pit connected to the sanitary drain
Correct answer: An approved location such as a storm drain, combined sewer (where approved), or daylight
Subsoil drain systems must discharge to an approved location, which can include a storm drain or an approved point of disposal such as daylight — not into the sanitary system.
Question 5: When sizing a storm drainage system under the IPC, which of the following factors is NOT used to calculate drain pipe sizes?
- Rainfall intensity in inches per hour
- Drainage area in square feet
- Soil percolation rate (Correct answer)
- Horizontal pipe slope
Correct answer: Soil percolation rate
Storm drain sizing uses rainfall intensity, drainage area, and pipe slope; soil percolation rate applies to subsurface absorption systems like septic fields, not storm drains.
Question 6: Under the IPC, when a roof has expansion joints, roof drains must be installed:
- Only at the lowest point of the entire roof
- With a single oversized drain at the center of the roof
- On each side of every expansion joint (Correct answer)
- With flexible connectors that span the joint
Correct answer: On each side of every expansion joint
Because water cannot flow across an expansion joint to reach a single drain, the IPC requires roof drains to be placed on each side of the joint.
Question 7: Per the IPC, a trap is required on a storm drain conductor when it connects to:
- Any roof drain regardless of the sewer type
- A storm-only sewer system
- A combined sanitary and storm sewer (Correct answer)
- Any underground piping system
Correct answer: A combined sanitary and storm sewer
When a conductor connects to a combined sewer carrying sanitary waste, a trap is required to block sewer gases from rising back through the storm drainage system into the building.
IPC Storm Drainage Systems 2
Per the IPC, what is the minimum allowable size for a roof drain?