Roof Water Drainage Design

A complex series of roofs and junctions makes roof drainage design more difficult.

Roof water drainage design.

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. Often the floor plan of a building is designed then a roof is fitted over the plan. Hence this is by far the most common roof drainage situation. Quantity and placement of downpipes.

Determine 100 year 1 hour rainfall rate used for location of building. 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. 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. And the provision of appropriate overflow devices.

Designing roof drainage roof drainage systems should be designed and detailed by a suitably qualified trade or professional in accordance with the bca and the australian standards. 50 000 4 400 11 36. 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.

Size vertical storm drainage piping. Particular reference should be made to the correct sizing of gutter. There are three types of drain systems commonly used on flat roofs. Or 12 drains required.

A roof s structural frame or deck should be sloped and drainage components like roof drains and scuppers should be included in the design. Each of these systems has its own pros and cons. 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. The most critical role of the drainage layer is to provide an adequate flow of water off the roof during and after rainfall.

Ipc provides four steps to size the roof drains on a building. The poor roof design means there will be a major concentration of water flow from a valley gutter in a constricted area. Take the roof s total square footage and divide by the total square footage handled by one drain. 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.

A typical commercial or multifamily residential building will utilize one of the following types of primary roof drainage. Green roof solutions offers many different drainage layer options depending on system goals regarding water retention. Of course the best designed flat roof has the correct amount of pitch to drain the water off naturally. Select number of roof drains and calculate the roof area sloped to each drain.

These will drain to somewhere near the center of the roof and down through the building to underground storm mains or a detention pond.