How Do Flat Roofs Drain

For larger flat roofs like those used for flats townhouses commercial buildings or schools it s common to have a drain placed inside the roof edge.

How do flat roofs drain.

These drains are like the drain at the bottom of your shower except that the roof drain has a larger strainer to protect it from debris. Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. An efficient low slope roof drainage system works entirely by gravity because water always seeks the lowest level. The most critical of these issues is the flat roof drainage systems.

Flat roof drains scuppers gutters and drainage systems on flat roofs. These drains are distinguished by having higher rims. The minimum slope the code allows is in 12 in. A flat roof may use interior drains to collect water from the centre of the roof.

Exception 1 of section 1511 1 states existing roofs do not have to meet the requirements of the code if positive drainage is provided. Along with the benefits of a flat roof come unique challenges. This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table. The result is the number of drains needed.

Roof drains for flat or low slope roofs come in a few standard types. The rationale for not requiring secondary drainage is that if positive drainage is provided that is adequate to drain the roof. A rooftop garden or additional outside living space are the top reasons people choose flat roofs. Unlike other roofing types that are slanted or sloped to allow water to drain automatically flat roofs need a built in drainage system to help remove moisture and debris.

As we will see in steps 3 4 the size of the roof drain lines is dependent on the square feet of the roof area being served by each roof drain. One of the most overlooked items on a flat roof is the draining system. In addition to the primary roof drains there will also be overflow drains which are used for redundancy and sized in the same manner. Inner drains gutters or scuppers each have their own function and deciding which system is best depends on.

Sizing the drains for each system including the number of drains required is based on. More attention should be given to the location of a drainage system to avoid future problems. Your building and location can help determine which drain will fit your roof needs. The above sizing data is offered as a guide only.

Take the roof s total square footage and divide by the total square footage handled by one drain. The one challenge with flat roofing is ensuring proper drainage. The roof is designed to have a gentle slope towards that drain from where the water is piped away from the walls and foundations. The roof slopes toward the center drain where pipes in your building channel the water into the sewage system.

A gravity drainage system on a flat roof differs from the gutter system you find on residential roofs in two key ways.