Roof Drainage System Design

The most critical role of the drainage layer is to provide an adequate flow of water off the roof during and after rainfall.

Roof drainage system design.

The design event used for sizing a roof drainage system will therefore not normally come out of a clear blue sky and then end equally suddenly but will have been preceded by a period of less intense rainfall. 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. To design a sloped or flat roof drainage system we need to know the anticipated maximum rainfall rate and the flat or projected roof area. 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.

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. A typical commercial or multifamily residential building will utilize one of the following types of primary roof drainage. There are various approaches that can accomplish this balancing act but each offers its own advantages disadvantages depending on a number of factors. Green roof solutions offers many different drainage layer options depending on system goals regarding water retention.

A roof drain system s primary function is efficient water removal but in most cases it must also offer aesthetic appeal and on deck workspace. Please see roof drainage calculations for a detailed answer to your question. Typically a steep slope roof slope is equal to or greater than 3 inches of rise per 12 inches of run 25. Establishing a minimum slope is critical because most steep slope roofing as.

Hence this is by far the most common roof drainage situation. I examined several roof drainage calculators and tables to see what they tell us. Design considerations to keep in mind. 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.

From the very dawn of building construction it has been necessary to incorporate some method of gathering and discharging rainwater from the roof of a structure.