How Much Roof Area Before I Need Roof Drainage

Vertical walls abutting a roof must be included in the catchment area.

How much roof area before i need roof drainage. An additional roof drain should be added for each 10 000 square foot area. The more roof surface above the gutters the more rainwater will be caught and funneled down into those gutters. Calculate the total roof area by multiplying its length by width. Refer to as nzs 3500 3.

The drains should be placed at a maximum of 75 feet in each direction away from each other. Dropping from the 5 drain in the table to a 3 drain cuts the serviced or drainable roof area to about 0 26 x the roof areas shown in the table. Calculate total roof area. 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.

Sizing the drains for each system including the number of drains required is based on factors such as the roof area the drain location s the inflow rate and desired drainage rate and the expected rainfall volume. Increasing from the 5 drain shown to a 6 drain increases the roof area that can be served by about 1 6 x the table data. Roof drainage systems design as nzs 3500 3. For hipped roofs with eaves gutters a simplified formula can be used to calculate catchment area but the slope of the roof must be known.

It can be argued that the minimum roof slope for drainage is 1 0 since this is sufficient to allow water to flow but there are other design considerations that must be taken into account when determining the final minimum slope. According to the international building code the typical built up flat roof that uses tar or asphalt goes by the guideline that for every foot 12 inches of a flat roof a minimum of inch must step up or down. This is the basis for calculating the angle which is approximately a 1 19 degree slope. A good rule to follow is to provide two roof drains for a total roof area less than 10 000 square feet.

There are 5 easy steps to figure out how many drains your commercial roofing project will need. A large roof is going to move a lot of water which means the downspout locations may need to be adjust to compensate.