Secondary drainage secondary or emergency roof drainage is required wherever the buildup of water is detrimental to the roof structure.
Secondary roof drain requirements.
This system shall be compliant with all federal state and local codes.
Where roof drains are required secondary emergency overflow roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.
If the sump is 2 or deeper the secondary drain shall serve as the primary drain totally defeating its purpose.
Ibc s secondary roof drainage requirement first was added in ibc 2009.
In either case the discharge shall be located so that it is readily visible by building occupants.
If they are used for secondary drainage then they should be a minimum of 2 inches above the roof level and a maximum of 4 inches above the roof level.
Secondary drainage was not required with ibc s previous editions.
When a secondary roof drainage system is installed it shall discharge independent of the primary building storm system and shall terminate a minimum of 18 above grade in an area that will be visible to the people who occupy the building.
Scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by section 1101 7.
A secondary drain placed in a sump will start working as soon as water reaches the top of the standpipe.
By the 1997 edition of the upc section 1101 11 2 had been added that completely prescribed where and how secondary roof drainage was to be provided.
According to the chart for 1 8 slope per 12 of pipe for 5 000 square feet of roof area with a 6 per hour of rainfall the required pipe size is 8.
Once the number of required drains for the area is determined the size of the drain inserts and plumbing should be established.
Using ibc 2009 or ibc 2012 it could be inter preted the addition of secondary drainage may be required during reroofing this was not the intent of the 2009 code change.
To size the vertical roof drain for the same parameters 5 000 square feet of room area and 6 per hour of rain consult table 1106 2 figure 3.
Where should the secondary drainage be discharged.
Secondary emergency roof drain systems shall be sized in accordance with section 1106 based on the rainfall rate for which the primary system is sized.
If the sump is shallower than 2 it will be full of standing water which may freeze and damage the drain and the adjacent roofing.
Overflow drains shall be the same size as the roof drains with the inlet flow line two inches above the low point of the roof and shall be installed independent from the roof drains.
This is completed using a plumbing calculation.
The rationale for not requiring secondary drainage is that if positive drainage is provided that is adequate to drain the roof.
