Secondary Roof Drainage Design

A standpipe or dam built within the secondary drain dictates the anticipated water depth.

Secondary roof drainage design.

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. Overflow scuppers can also act as secondary drains at the perimeter of the roof. Scuppers shall not have an opening dimension of less than 4 inches. 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.

An essential of good design. A scupper can be a piped penetration in the parapet wall as in figure c. Scuppers shall have an opening dimension of not less than 4 inches 102 mm. Select number of roof drains and calculate the roof area sloped to each drain.

Roof drainage is one of the fundamental considerations of building design. Size horizontal storm drainage piping. The width of the opening must be equal to the circumference of the drain required. A secondary roof drain achieves its function by controlling the water build up.

An open sided roof area used for secondary roof drainage can be just a simple opening in the parapet wall surrounding the roof. For example if the roof drain is 4 in the opening of the scupper or the open sided roof opening must be 12 56 in. Scuppers are typically easier to install. From the very dawn of building construction it has been necessary to incorporate some method of gathering and discharging rainwater from the roof of a structure.

The secondary drain is typically placed about 1 2 above the depth of water above the primary at its design flow. Secondary drainage shall be provided through the use of sidewall scuppers or internal roof drains. Secondary drains during a roof replacement proj ect. The premise of the pattern is that a drain is positioned in the center of the rectangular area and there is a four way positive slope into the drain.

Size vertical storm drainage piping. In either case the discharge shall be located so that it is readily visible by building occupants. Determine 100 year 1 hour rainfall rate used for location of building. The most dependable type of roof drainage design is the inverted pyramid pattern.

Because of that no certain distance exists. When either method is used they must be sized by table 1101 12. 3 398 380 540 380 5 3 06 in order for the 6 drain to handle the necessary flow there will be a depth of 3 06 of water above the primary drain at its peak design flow. Secondary drainage secondary or emergency roof drainage is required wherever the buildup of water is detrimental to the roof structure.

This type of pattern is particularly useful on buildings that are easily divided into rectangular areas.