Flat Roof Rainwater Drainage Calculations

Upon completion a full set of rainwater drainage design calculations are provided confirming the.

Flat roof rainwater drainage calculations.

Alumasc s leading drainage calculator allows architects specifiers and building engineer s to design and quantify all their rainwater drainage requirements using this dedicated software. Take the roof s total square footage and divide by the total square footage handled by one drain. The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout. 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.

The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. 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. F x p a 4 estimate the rainfall per event in your area r by dividing the annual precipitation rate by the number of rain days per year. The result is the number of drains needed.

Our online tools have been designed with simplicity in mind removing the need for any prior specialist industry knowledge. The first step in sizing a roof drain is to calculate the surface area of the roof that the drains will be covering as well as the average hourly rainfall rate at the building location. 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. Calculate drains needed.

Box gutter with rain water head at end of box gutter. Category 2 and 3 flat roof drainage linked to local rainfall data. This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table. 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.

The full flow capacity of a drain is not realized until the water reaches approximately 2 5 above the inlet in a four inch drain and 3 5 in a six inch drain. The above sizing data is offered as a guide only. Drain calculator factors which affect proper roof drainage are deck slope drain size and placement of drains. Multiply the area of your roof by the total obtained in step 2 as outlined in the following equation.