Floor drains often carry petroleum products and high concentrations of contaminants from inside the building. Most communities have specific regulations governing where the discharge from the drain goes. Homeowners should check with the local building code officials to determine what requirements they must follow. Generally, they cannot be drained into municipal sewers. Businesses with floor drains have more rigorous rules because they often have higher concentrations of contaminants going down the drains. Communities now require business floor drains to empty into phase traps where solvents and contaminants lighter than water float to the surface, while the outlet pipe going to the sewer or holding tank only allows fluid from the center of the liquid to pass through. Certain kinds of businesses have requirements to send all floor drain discharge to holding tanks where it is periodically pumped out for proper disposal.
The primary requirement for floor drains is that they must be able to drain. That means the outlet has to be lower than the inlet, or there has to be a cistern with a pump between the two. A secondary requirement is they must have P-traps. Traps prevent unwanted and hazardous gases from rising through the pipe and entering the building. Floor drains that are not used much can benefit from a trap primer. This is a small tube installed with the trap that is connected to a cold water plumbing line. The primer tube drips water into the trap so it stays full. The floor has to slope toward the drain, otherwise liquids will puddle. In most cases, a very gradual slope of ¼ inch for every 10 feet is adequate, but this has to be calculated based on the maximum flows expected.
The most widely used material for floor drains is PVC. A typical assembly includes a floor drain body. This comes with or without the grate and attaches to the P-trap. The P-trap attaches to the outlet pipe. Outlet pipes for residential use inside homes will often use 2-inch pipe while garages, patio areas and balcony or roof deck drains will use 3- or 4-inch pipe. The grates that go over the drains have to be made of an appropriate material for the loads that will be on them. Garages usually have metal grates while those in the floor of a home or on a patio will often be plastic.
Commercial floor drains have to use materials and components that match the job. Some may need to use stainless steel components and others may have to use components like vandal proof drains, waste funnels and sediment traps. If the floor drain empties into any kind of holding tank or phase trap, it has to be vented with a separate pipe that rises above the building’s roof.