Assume you are tasked to size a horizontal roof drain serving 5 000 square feet of roof area on a building located in dallas tx.
Minimum roof area before i need roof drainage.
It is a requirement of building regulation part h that adequate provision is made for rainwater to be carried from the roof of the building.
Increasing the angle of a flat roof will always increase the speed of water movement across the surface.
Determining the exact roof area and the number of drains is precise work so it requires coordination with the building s architect.
A good rule to follow is to provide two roof drains for a total roof area less than 10 000 square feet.
For a large roof it is recommended to have drains placed at multiple locations within the area of the roof.
Evidently there are set standards for the different kinds of roof slopes.
Minimum roof pitch the minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run.
Roof drainage systems need to be designed to cope with the rainfall intensities for the specific building location.
Drainage design specific to location.
Walls that drain onto a lower storey roof can increase the effective roof area by around 50.
Rainfall intensities vary throughout new zealand and are often very high.
The drainage system of any roof can be located at the edge or in the middle of the roof.
An additional roof drain should be added for each 10 000 square foot area.
Adding a roof can create drainage problems if the roof pitch is too shallow.
A small roof with a shorter length on the other hand will not collect a lot of water within a short period of time and will work just fine with the minimum roof slope for drainage.
Calculate total roof area.
Once the drainage system is determined the designer must ensure positive drainage by correctly positioning the roof drains.
Determine leader or pipe size.
Calculate the total roof area by multiplying its length by width.
It s easier to see how this works with a real world example.