Plumber's Licensing Exam: Storm Drainage

This guide will help you to identify the storm drain system exclusive of the sanitary drainage system, as well as the drains and fixtures that are permitted or not permitted to drain into the storm drain system. Removal of storm runoff, which belongs in the storm drain systems, from the sanitary drainage systems has been an ongoing concern in many communities. It is critical that municipalities not have their sewage treatment plants be overburdened by excess storm water. The sewage treatment plants would have to be unnecessarily oversized or untreated sewage would overflow into the environment.

Objectives
- Recognize where storm drains are required
- Identify the materials allowed for storm drains
- Explain when secondary roof drains are required and state their design parameters
- Name the requirements for subsoil drains, sumps, and sump pumps

Key Terms:
conductor
flashing
primary roof drain
scupper
secondary roof drain
subsoil drain
sump
sump pump

General Requirements
All of the flat, man-made areas we have created must be drained of storm water in an efficient and reliable manner. Almost all localities require that all roofs, paved areas, yards, courts, and courtyards must drain to an approved location. (Refer to IPC 1101.1–1104.3; UPC 1101.1–1101.11.1)
No storm water can drain into a sanitary sewer system that is intended only for sewage. This includes the majority of the sewers in American cities today. This also involves disconnecting all of those illegally connected sump pumps and roof drains that are presently connected to the sanitary sewer.
Some areas still have combination sewers that are designed for sewerage as well as storm water runoff. These combination sewers can become overtaxed, more often than not, when it rains heavily. Raw sewage ends up flowing to waterways, and into lakes and oceans, without being properly treated.
Conductors, which are the pipes inside a building that move storm water from roof drains, must be tested to the same standards as a sanitary drainage system. During heavy rain or combination rain and snowmelt, the conductors and building storm sewer are subjected to a more strenuous load than any sanitary system would be. Imagine the damage that would occur if a conductor failed inside a building.

Real-Life Situation: For years now, every time it rains hard, the Springfield Shopping Mall has had water flowing out of the secondary roof drains. The maintenance department is at a loss as to how to correct the problem. The new owners of the mall want a quote from Ace Plumbing to correct this problem, which has the potential to cause a catastrophic roof cave-in. The mall owners expect the repairs to be costly, but they want the roof fixed correctly once and for all. The reputation of Ace Plumbing Company will be on the line with this very visible job. What are the challenges that Carlos and Sophia face in getting this job done right the first time?

Caution: If a building is in an area prone to heavy thunderstorms, careful attention needs to be paid to adequate sizing of the system. An average per hour rainfall amount will do little good when all of that average hourly rain falls in a 5-minute period. The system must be sized to handle the highest rainfall rate for a short period of time.
Like sanitary sewers, no reductions in pipe diameter are allowed in a storm system. All the fittings used must be approved drainage fittings applicable to the piping material being installed.
Both the UPC and the IPC require that every roof be designed to withstand the weight of the maximum water depth that could ever pool on it. This requirement will also be found in all local building codes. This must be calculated assuming that all of the primary roof drains are plugged, and the roof has to rely on the secondary drains with the depth elevated enough to have water flow out through the secondary drains. So what does roof design have to do with plumbers? This rule is obviously for builders, but as a plumber, you must be aware of it and alert to the potential for primary roof drains to become plugged, and what needs to be done to ensure the drainage system works.
The primary system is the roof drains, which drain through the conductors to storm sewer system. The secondary system, which must be completely independent of the primary system, simply drains through scuppers or over the roof edge to the ground below. The secondary drainage must flow where it is obvious to building personnel so they are made aware that the primary system is not working and needs attention.
The storm drain system needs cleanouts placed within it in a similar manner as the sanitary sewer. Subsurface drains, which drain water away from building footings and foundations, are an exception to this rule.
If a storm sewer is susceptible to backflow, a backwater valve must be installed. This is especially important for combination sewers.
The materials and installation methods used for conductors and underground storm drainpipe must meet the same requirements as those for sanitary drainage. The materials used in the storm sewer, which is the portion of the main storm drain that is outside the building, must be of the types and grades found in the table below.

The materials used for subsoil drainage systems must be those found in the second table. Subsoil drains must be made of either perforated pipe or horizontally split pipe, or installed with open joints.

If a storm drain is installed in a combined sewer with a sanitary system, a trap must be installed in the storm system just before it connects with the sanitary system. This one trap is simply intended to keep sewer gas out of the storm drain system.

Trap sizing for a storm system is simple:

Make the trap the same size as the storm drain. And you always install it on the building side of the sanitary system.
Sanitary systems and storm drain systems must remain completely independent except for cases where there is a combination sewer. Even when a combination sewer is involved, the piping systems must still be completely independent of each other, except for the point at which the storm drain connects to the sanitary system. This connection must be made using a wye fitting, and it must be at least 10 feet downstream of any stack. This connection procedure enables the sanitary system to function normally, even during heavy rainfall.
Floor drains cannot be connected to a storm drainage system. If a below-grade window well requires a drain, it will not be considered a floor drain so that it can be connected to the storm drain system. A parking garage that has no chance of being used for automobile repairs can have the drains in the floor connected to the storm drain system. Floor drains in multilevel parking garages are no longer required to have individual traps, provided the drains are connected to a main trap before discharging to a combined sewer.

Roof Drains
Roof drains shall be installed in accordance with the manufacturer’s instructions. The inside opening for the roof drain shall not be obstructed by the roofing membrane material.

The table below (Dome Area Comparison Table) must be used for sizing purposes of the strainers. Roof drains need strainers that are at least 4 inches tall. The diameter of the strainer must be at least 11/2 times the diameter of the roof drainpipe. Think of all the stuff that lands on a roof—leaves, paper scraps, plastic grocery bags, to name a few. All of these items must be kept far enough away from the drain so that rain can drain down the pipe. If the roof is used for human activities or parking, the strainer will be flat, but it must now be increased to at least two times the diameter of the drain. If there is a collection of debris on the drain, we must assume the folks who use the roof will notice it and clear it. (Refer to IPC 1105.1–1110.4; UPC 1105.3, 1106.4, 1108.0)
There is a new technology, called symphonic roof drainage systems, which originated in Europe and is now being used with much success throughout the world. It is made up of roof drains with air baffles that comply with ASME 112.6.9. All types of roof drains must have a leakproof flashing to prevent leakage into the building.
Sizing for the storm-water conductors and leaders, both horizontal and vertical, must be done according to rainfall charts available from the National Weather Service. These charts are also found in your plumbing codebook, which is handy since you can most likely take it with you into your test.

Tips
Expansion joints are an important part of a roof drain system. The height of a roof changes constantly due to temperature changes and the settling of the building. The base of a conductor is generally firmly mounted to a storm drain that is buried in the earth. An ideal place for an expansion joint is immediately beneath a roof where the roof drain body connects to the leader. This configuration allows the roof assembly to move without putting physical stress on any part of the storm water drainage system.

Fact: The first building code concerning roof construction was written by King Hammurabi of Babylon about 1780 b.c. The law concerning building construction was as follows: “If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death.” The possibility of a roof collapse is a real threat. If a flat roof with an area of 5,000 square feet is covered with 2 inches of water, that means it is holding 833.33 cubic feet of water on it. That amount of water weighs approximately 26 tons!
The slope for the building storm drain and storm sewer must be between 1/8-inch per foot and 1/2 -inch per foot.
Keep in mind that whenever a vertical wall is in a position that forces the rain that strikes it to land on the roof, one-half of the surface area of that vertical wall must be added to the area of the roof being drained.
Now, let’s get back to those secondary roof drains mentioned earlier. If the design of a roof creates a surface that will pool with water when the roof drains are plugged, then secondary roof drains are necessary. Commonly, scuppers are installed as part of the construction of the upper area of the building wall. The area of the openings is three times the area of the primary roof drains. Any secondary roof drainage system must direct the rainwater to an area above grade that will be noticed so the primary roof drains can be cleaned or repaired.

Subsoil
As stated earlier, subsoil drains must be open-jointed, horizontally split, or perforated pipe. This design allows for an almost continuous area of drainage for the subsoil area. The minimum pipe size for a subsoil drain is 4 inches in diameter. The subsoil drain can drain to an approved grade area or to a sump where it can be pumped out to an appropriate drainage area. The sump pit for subsoil drains does not require the gastight cover and vent that a sanitary sump does since there is no sewer gas to contend with. (Refer to IPC 1111.1; UPC 1101.5.1–1101.5.6)

Building Subdrains
If a building subdrain is below the level of the storm sewer or other approved area of disposal, it must drain to a sump where it can be pumped out to an approved disposal location. The sump pump must be sized to handle the anticipated inflow and it must be capable of overcoming the head needed to lift the water to a place of disposal at the anticipated flow rate. (Refer to IPC 1112.1–1113.1.4)
The sump pit must be at least 18 inches in diameter and 24 inches deep. It must be made of an approved material, and its floor must be able to be a permanent support for the pump and the piping attached to it. This rule prevents anyone from simply digging a hole and dropping a pump into it. Neither soil nor gravel can be used as a permanent base for the pump.
The discharge pipe from the sump pump must be at least as large as the pump outlet, and the pipe must also incorporate a full flow valve and a check valve close to the pump.