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Roof drains are designed to avert water from pooling on the roof’s surface and prevent roof damage. They do this by diverting water from your roof to the ground. Roof drainage is often overlooked when roof maintenance is carried out, which leads to roof decay. Koala Roofing show’s how essential it is to maintain your roof drainage, so we have put together four different methods that our flat roof customers can employ to drain water from their roofs. 


A flat roof is a popular style of roofing. Flat roofs are almost level in contrast to other types of roof styles that are sloped and steeped. Because of this lack of deep sloping, flat roofs harbor stagnant water and clogging, leading to leakage.

So, if you choose to install a flat roof for your home, here are different ways you can drain it.

1.       Siphonic roof drain.

A siphonic roof drain system is usually used for flat roofs because it drains water faster than other drain system types.

A good siphonic roof system contains an air baffle that prevents air and debris from entering the piping system; the water is then sucked at high velocity into the drain. The drainage process is made exceptionally efficient by the void of air in the piping system and the downward pull of the water. 


  • A siphonic drainage system comprises fewer outlets, downpipes with shorter pipe lengths which reduces installation costs.
  • Fewer downpipes and outlets mean freed up space on the roof.
  • Higher efficiency due to the absence of air in the pipes
  • It makes for easy maintenance as it is essentially self-cleaning due to the high velocity of water passing through it.


  • The major disadvantage is that the small diameter of the pipes allows for blocking by detritus-like leaves. And if not maintained, it can result in damage to the system.

2.       Gutters

Source: “Gutters” by Chris Riley – Under the Creative Commons License

A gutter is a trough placed on the edge of the roof that drains excess water and feeds into a downpipe. Its function is to prevent water from flowing or dripping off roofs uncontrolled -on persons standing below or entering the building and damaging the walls. A gutter’s longevity is only as good as the material used, the most common being aluminum, vinyl, and galvanized steel.


  • Gutters help protect the building’s foundation and basement from erosion by keeping it dry.
  • They are relatively inexpensive.
  • Gutters protect the roof from damage by channeling water away from the roof after heavy rainfall.


  • Requires frequent maintenance as it can get clogged very quickly. Leaf guards can be used for easier cleaning.

3.       Inner drains

These are used mainly on commercial buildings and buildings with large roofs. They are placed under the roof and shuttle water away. Inner drains are usually positioned at the center of the roof or towards the roof’s slope. They also have protective barriers that keep debris from entering into the pipe.


  • Inner drains do not pose visual hindrance and allow for complete use of the roof as they are placed below it.
  • They are suitable for colder climates as their pipes don’t freeze.
  •  If there is leakage in the pipe, no damage is incurred to the property as water will continue to drain.


  • Inner drainage systems are expensive.
  •  Maintenance and repairs are costly because the pipes are placed underneath the roof.
  • Pools of water can form on the roof and eventually find a way into the building if there are clogs in this drainage system.
  • When the screen of the inner drain is neglected during cleaning, it causes a large pond to form.

4.       Scupper drainage system

Source: “Blue on Blue” by Theen Moy – Under the Commons License

A scupper drain consists of an opening in the wall which allows water to drain from the roof to the downstairs gutter and a scupper. They prevent water pooling within the curbing or walls of a building. Scuppers are used in apartments and commercial buildings and sometimes in residential homes constructed with flat roofs.


  • They are relatively inexpensive
  • They are easy to maintain 
  • Twigs and leaves do not easily clog a wide scupper


  • Small scuppers clog easily and pooled water spills over the roof edge
  •  If the scupper drain is not connected to a downspout, the water can erode the foundation as it falls


A flat roof is a good roofing option, but they do not drain as quickly as the other roofing types. So if you have a flat roof, explore one of the drainage systems above and carry out regular roof checks to protect your roof. 

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