Secondary Roof Drainage Design

Select number of roof drains and calculate the roof area sloped to each drain.

Secondary roof drainage design. The most dependable type of roof drainage design is the inverted pyramid pattern. This type of pattern is particularly useful on buildings that are easily divided into rectangular areas. Determine 100 year 1 hour rainfall rate used for location of building. Size vertical storm drainage piping.

Secondary drains during a roof replacement proj ect. 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. Roof drainage is one of the fundamental considerations of building design. 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.

An open sided roof area used for secondary roof drainage can be just a simple opening in the parapet wall surrounding the roof. The width of the opening must be equal to the circumference of the drain required. Secondary drainage shall be provided through the use of sidewall scuppers or internal roof drains. A secondary roof drain achieves its function by controlling the water build up.

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. Scuppers are typically easier to install. When scuppers are used for secondary emergency overflow roof drainage the quantity size location and inlet elevation of the scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by section 1611 1. A standpipe or dam built within the secondary drain dictates the anticipated water depth.

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. 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. When either method is used they must be sized by table 1101 12.

In either case the discharge shall be located so that it is readily visible by building occupants. An essential of good design. 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. Because of that no certain distance exists.

Secondary drainage secondary or emergency roof drainage is required wherever the buildup of water is detrimental to the roof structure. Scuppers shall not have an opening dimension of less than 4 inches. Ipc provides four steps to size the roof drains on a building. 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.

The secondary drain is typically placed about 1 2 above the depth of water above the primary at its design flow.