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The Importance of Drainage for Commercial Flat Roofs

The Importance of Drainage for Commercial Flat Roofs

December 10, 2021

A flat or sloped roof on any commercial building needs a specific drainage system installed by flat roofing contractors. If you don’t use the services of a professional, a flat roof repair will be required for your flat roofing in Toronto. Keep in mind when you don’t have adequate water drainage from your roofing system, flat roof replacement contractors will be needed to sort out the problems that accompany the lack of drainage.

Using a professional will provide a safety net of sorts for your building because a properly installed drainage system can help a roofing system last 15 years with a solid maintenance schedule. Flat roofs afford many advantages for a building owner, but you must get the drainage right, or you will see ponding and leaks develop because you don’t have the right water management system on your roof.

Why is Drainage Important for a Commercial Flat Roof?

When you have a flat roof or a slightly pitched roof, gravity will not move water from the roof to the ground. Your roofing system must be outfitted with a drainage system that carries water from the roof to the ground to prevent water ponding that eventually leads to leaks. That and caulking are where you are vulnerable on the roof, and the tiny crack in either substance becomes the leak that wreaks havoc in your commercial structure.

During winter months, the freeze-thaw cycle and the weight of snow will put extra weight on your roof – something your roof wasn’t designed to withstand. Structural damage can ensue from the crushing weight of the snow. Another place that can be a hazard for a flat roofing system is the vents and chimneys – these two items are access points for water. They must be monitored regularly to prevent invasive water from making its way into the building.

Problems Caused by Ponding or Standing Water on a Flat Roof

Ponding water on a roof causes many problems that building owners aren’t aware of, and that is where the problems begin. And costly repairs follow when the issues aren’t identified and dealt with promptly.


Commonly, birds will build nests on rooftops, and if you provide a habitat for them to nourish themselves like a pond to drink from, they will stay on the roof. You must take steps to make your roof less hospitable for birds because it will reduce maintenance and repair costs in the future.


Standing water is a mosquitoes’ best friend. It is a breeding ground where they can multiply and proliferate. Mosquitos carry disease and are an annoyance, and when you have standing water, you can count on a high degree of mosquito infestation.

Plant Growth

When you have water on the roof, it isn’t just mosquitoes you have to worry about. Water will help plants grow on your roof, and with the growth of the plants comes another problem. No matter how small, growing plants will clog drains and help create pools of standing water that develop leaks.

Fungal Growth

Moss, mold and mildew prefer wet conditions, and when they are present, damage to roofing materials comes to the forefront.

Wear And Tear on The Roofing Materials

If you have a ponding problem and your roof is a membrane system, you could be in for a big surprise. Ponding water erodes roofing membranes, and the allowance of ponding can void a warranty if you don’t perform proper maintenance for the roofing system as a whole.

Types of Flat Roof Drainage Systems


Using gutters to drain water from the roof is a tried and successfully tested method for roof drainage. Open gutters along the roof edge can move water well and help eviscerate ponding problems on a roof. The pros of a gutter system include the cost, very inexpensive, and installation is easy. The cons of the gutter system are more maintenance to keep the gutters open. In the winter, debris can be frozen into the channel reducing its effectiveness and cleaning the gutters can be challenging.

Roof Drains

Drains have come a long way since their inception and can be attached to an internal system that runs water away from the building to the ground. The drains are placed in strategic areas and covered with a filter to keep debris from clogging the system. The advantages of the roof drain consist of all seasons’ drainage. The pipe network is protected from water that can freeze in the winter, and the curb appeal of the system is excellent. The drainage system is out of sight and out of mind when you look at the roof. Drains are an expensive proposition from installation to maintenance, and they cost money for upkeep. Clogs can be a nightmare if the right strainers aren’t used, creating extra maintenance costs for a building owner.

Scupper Drains

Scuppers say value for money like no other roof drainage system. They are installed at the parapet walls and form a seamless drainage system through interconnection with downspouts. Scuppers are a roof’s best friend from a maintenance standpoint – they require little or no maintenance to keep the drainage system working at peak efficiency.  From a dollars and sense point of view, scuppers offer the best value for money for any drainage system on the market. On the downside, scuppers need to be installed on a sloped roof to get the water moving to the ground. Snow is a challenge for scuppers, but they offer the best option for heavy rainfall.

Hire Our Experts to Identify Any Problems in Flat Roofs

The Importance of Drainage for Commercial Flat Roofs When you work with Integrity Roofers to solve your roof drainage problems, you can count on a team of seasoned professionals to complete any work necessary. We have two decades of service in the business, offering the best roofing advice in the Greater Toronto Area. Our counsel is above reproach, and we will recommend the best course of action for your roofing system. When you bring our company in, we will take a full roofing system view and advise you about your current situation and what you can expect going forward in the area of maintenance and or replacement for your roofing system. To get an idea of the cost for your flat roofing work, please complete our estimate form for a comprehensive look at the total costs. If you want to speak to a roofing expert, call our office today at Integrity Roofers at 647.953.9365.

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