How far should a primary roof drain be located from the secondary drain?
A secondary roof drain achieves its function by controlling the water build-up. A standpipe or dam built within the secondary drain dictates the anticipated water depth. Because of that, no certain distance exists. If, for example, the standpipe is 2″ high, and the secondary drain is 6 feet away from the primary drain, the depth of water will be approximately 3 1/2″ (if the 1/4″ pitch is maintained) before it reaches the standpipe’s top. If the primary and secondary drains are located at the same elevation (in a valley), the standpipe height alone will dictate the water depth. It is very important not to place secondary drains in any kind of sumps. A secondary drain placed in a sump will start working as soon as water reaches the top of the standpipe. If the sump is 2″ or deeper, the secondary drain shall serve as the primary drain, totally defeating its purpose. If the sump is shallower than 2″, it will be full of standing water, which may freeze and damage the drain and the adjacent
