How Do Flat Roofs Drain

The minimum slope the code allows is in 12 in.

How do flat roofs drain.

An efficient low slope roof drainage system works entirely by gravity because water always seeks the lowest level. More attention should be given to the location of a drainage system to avoid future problems. Exception 1 of section 1511 1 states existing roofs do not have to meet the requirements of the code if positive drainage is provided. In addition to the primary roof drains there will also be overflow drains which are used for redundancy and sized in the same manner.

The result is the number of drains needed. The one challenge with flat roofing is ensuring proper drainage. Take the roof s total square footage and divide by the total square footage handled by one drain. The best type for the application depends on several factors such as the size and slope of the roof the desired appearance and how much regular maintenance the drain system might need.

The most critical of these issues is the flat roof drainage systems. A gravity drainage system on a flat roof differs from the gutter system you find on residential roofs in two key ways. The roof slopes toward the center drain where pipes in your building channel the water into the sewage system. 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.

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. Calculate drains needed. 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. The above sizing data is offered as a guide only.

The rationale for not requiring secondary drainage is that if positive drainage is provided that is adequate to drain the roof. Sizing the drains for each system including the number of drains required is based on. Along with the benefits of a flat roof come unique challenges. These drains are distinguished by having higher rims.

Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. Internal drains are often placed in low slope roofs when the roof span does not make a single slope practical. One of the most overlooked items on a flat roof is the draining system. The roof is designed to have a gentle slope towards that drain from where the water is piped away from the walls and foundations.

Flat roof drains scuppers gutters and drainage systems on flat roofs. A flat roof may use interior drains to collect water from the centre of the roof. Your building and location can help determine which drain will fit your roof needs. Roof drains for flat or low slope roofs come in a few standard types.

This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table.