You cannot, however, use the existing trap. Floor drains or area drains, when used to drain exterior areas, should have an open area equal to twice the transverse area of the connecting pipe (table 1.) see roof drain section for rainfall and sizing data table 1
Floor drains required can be determined only after careful review of the plans and anticipated building use.
Floor drain p trap size. As a general reference, floor drains should be sized to handle an overflow condition of water that may be discharged onto the floor. The size of floor drains is important as it affects the number of drains required and the amount of water which can be efficiently drained. Grate free area is defined as the total area of the drainage openings in the grate. the drain outlet should be sized large enough to safely discharge the maximum.
This is an advantage in for a floor drain, the minimum trap size is 2 inches. If your trap has mechanical joints, they must be in the open for maintenance purposes. Sufficient top size and grate free area to pass the anticipated flow are required.
How to select a floor drain floor drains are primarily used for inside locations where the flow rate into the drain can be anticipated. The fixture drains for water closets, trap standard service sinks and pedestal urinals with integral traps shall not be less than 3 inches. The chart below illustrates water outlets and the demand (gpm) requirements.