Roof Drainage Calculations Flat Roof

A minimum 4 inch vertical drain is required.

Roof drainage calculations flat roof.

Using tools from the international plumbing code ipc it s not that hard. Determine 100 year 1 hour rainfall rate used for location of building. The maximum rainfall rate anticipated in the area where the building is located the flow in liters per minute per square meter for some x number of minutes. Upon completion a full set of rainwater drainage design calculations are provided confirming the.

2 500 4 x 3 75 2 344 sq ft. The tools guide the user step by step allowing fast and simple roof drainage design whilst ensuring full compliance with bs en12056 3 rainwater drainage design standard. The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. Size and placement of rooftop equipment may necessitate additional roof drains.

Enter table 1108 1 until you find a diameter pipe that will carry 2 344 sq ft. For single vertical walls affecting the collection area of a roof drain add 50 percent of the side area to the total for calculating the flow rate. Our online tools have been designed with simplicity in mind removing the need for any prior specialist industry knowledge. Select number of roof drains and calculate the roof area sloped to each drain.

The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. For multiple walls use 50 percent of the maximum projected area of all walls. 2 3 4 5 6. When placing roof drains it is good design practice to locate the drains no more than 50 feet from the roof perimeter nor more than 100feet apart.

To design a sloped or flat roof drainage system we need to know several things. For single curved vertical walls use 50 percent of the maximum projected area. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall. Calculate total roof area.

Calculate the total roof area by multiplying its length by width. Step by step instructions step 1. 2 3 4 5 6 and 8 in. To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this.

It is important to remember that no roof area should ever have less than two roof drains.