Roof Water Drainage Design

Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally.

Roof water drainage design. Or 12 drains required. It is important for architects plumbing engineers and civil engineers to work together to design a system that will properly drain rainwater from a building and site. Commonly used on flat commercial roofs siphonic drains allow for a minimal number of drains and all of the drains can be connected to a single leader. Select number of roof drains and calculate the roof area sloped to each drain.

A roof s structural frame or deck should be sloped and drainage components like roof drains and scuppers should be included in the design. Determine 100 year 1 hour rainfall rate used for location of building. 50 000 4 400 11 36. Particular reference should be made to the correct sizing of gutter.

The result is the number of drains needed. Size horizontal storm drainage piping. The poor roof design means there will be a major concentration of water flow from a valley gutter in a constricted area. Each of these systems has its own pros and cons.

Size vertical storm drainage piping. Often the floor plan of a building is designed then a roof is fitted over the plan. There are roof coating products available if there isn t enough slant or slope to accomplish this. The design of the different drainage layers allows for a portion of the stormwater to be retained above where the water is allowed to flow freely off of the roof.

For most dwellings you ll find that gutters range in size from approximately 100mm diameter to 150mm diameter assuming gutters with a half round section profile and downpipes range from approximately 60mm diameter to 90mm diameter assuming circular downpipes. These will drain to somewhere near the center of the roof and down through the building to underground storm mains or a detention pond. Take the roof s total square footage and divide by the total square footage handled by one drain. Hence this is by far the most common roof drainage situation.

And the provision of appropriate overflow devices. The most critical role of the drainage layer is to provide an adequate flow of water off the roof during and after rainfall. There are three types of drain systems commonly used on flat roofs. In addition secondary or emergency drains may be required by local plumbing codes to help reduce the risk of a structural failure due to clogged drainage systems.

Ipc provides four steps to size the roof drains on a building. A siphonic roof drain utilizes siphoning as a drainage mechanism resulting in drainage that is faster than that on any other type of roof drain. The result can be an overly complex roof that is difficult to both construct and drain. A complex series of roofs and junctions makes roof drainage design more difficult.

A typical commercial or multifamily residential building will utilize one of the following types of primary roof drainage.