Drainage Solutions for Flat Roofs

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Many buildings in Canada have flat, or low slope, roofing systems. These are generally commercial buildings and industrial buildings , though some residential units also have flat roofs. This integrity of this type of roofing system depends greatly on sufficient drainage, as rain and snow melts can pool on the roof without it. This sitting water, or ponding, can cause a significant amount of damage to the flat roof system. As this water freezes, damage to the roofing membrane can occur. These flat roofs are also at a higher risk of algae development, and deterioration if this water does not have a proper avenue for drainage. Considering what these flat roofs are often protecting, by ensuring that your flat roof has sufficient drainage, you can reduce the risk of costly damage to the interior of the building.

Here are the three best drainage solutions for use on flat roofing systems:

Interior Drains

  • This type of drainage system is composed of drains placed in close proximity to the center of the roof, with pipes and gutters installed inside of the roof. This helps to push the water to the exterior of the roof. This type of drain is generally covered, in order to prevent any garbage or debris from entering and blocking the waters path. This drainage solutions will work best for large flat roofing systems that may have an ongoing issue with water pooling in the center. They are easier on the eyes, as the entire drainage system is hidden inside the roof itself. The cost for a drainage system like this one can be quite high. Though that may turn many building owners off, the investment will likely pay off in the long run, when water damage is no longer an issue.


  • This type of drainage system is placed on the exterior edge of the flat roofing system. It collects water drained from the rooftop, and directs it away from the building. Scuppers help to keep the water away from the side of the building, and its foundation, to prevent any structural water damage. This drainage system is a popular choice with building owners as it tends to be a more cost-effective solution than inner drains. Scuppers are most effective if the flat roof is designed to direct all of the water to the edges of the flat roofing system. Scuppers can be quite effective for flat roofs that are in a climate that receives frequent heavy rains. Though they may not be the best choice if you live in a climate that receives a lot of snow, as it may not handle the melts effectively.


  • This type of drainage system consists of open pipes that attach to the exterior edges of the flat roof. Gutters collect the water that drains from the roof, and like scuppers, direct it away from the building. Gutters are often the least expensive of any of the drainage options. This is because they can be installed on the edges of the flat roof after the roof is done, without any work needing to be done to the flat roof itself. Gutters are also effective for both heavy rains, and snow melts. Just like any drainage system, gutters must be cleaned regularly to prevent the build-up of debris.

There are many factors that will determine which drainage system will be most effective on your flat roof. The building engineer will likely be able to provide you with their opinion on the best possible choice. Ensure that the roofing contractor that you hire for the job, has the experience necessary to properly install any of the three drainage options above. Professional installation is key to ensuring that your drainage system is able to function properly, and provide your flat roof with the protection that it needs.