Flat roofs have a number of advantages, although these depend on each application. They can make a commercial building seem less imposing, because there is less bulk.
However, their lower cost compared to pitched roofs is often the decider. But this form of drainage can also be more challenging, and so we discuss three flat roof drainage options today.
Other advantages building owners may consider include longer lifespans before replacement, less maintenance, and convenient locations for HVAC plant and solar panels.
So why don’t we see more flat roofs everywhere we go? The answer could be a blend of conservatism, and the fact that rain water and snow melt are more likely to cause damp below.
The Downside of Flat Roofs: Drainage
Sloping, and pitched roofs are popular because gravity ensures natural drainage. They are also less-likely to leak, because there are far fewer places for water to pool.
Flat roofs have none of these advantages we just mentioned. Gravity has almost no effect at all. The best the building owner can do is insist on a gentle slope, and ensure that the water can easily flow away.
Three Main Flat Roof Drainage Options
All flat roof drainage systems slope to collection points, from where the water drains in a controlled manner. There are three options in our industry, although the details may vary because of the building and its immediate environment:
- Scupper drains protrude through parapet walls above roof level, and discharge freely, or via downspouts outside.
- Internal drains, often towards the center of a roof collect the water, and discharge it via an internal outlet.
- Flat roofs without parapets slope to walls on one or more side, where they discharge freely into eaves troughs.
Which Is the Best Drainage For You?
Flats roofs don’t drain rain water and snow melt as efficiently as sloping roofs do. That’s why we always discuss the pros and cons with clients when discussing one of these three flat roof drainage options:
- Scuppers are a budget-friendly option that’s popular in Calgary, although they need regular maintenance to ensure storm debris does not block the catchment points. We often fit down pipes to scuppers on houses with flat roofs, to lead the water to tanks.
- There’s not much we can easily do to improve flat roof internal drainage, except to install rooftop strainers to prevent storm debris entering the pipes. Maintenance and modification are expensive. This is not a drainage system we would usually recommend.
- Conventional gutters could be the best solution, provided the roof slopes suitably, and there is no surrounding parapet. They are easy to install, and, in our experience, the least likely to block, although they do benefit from annual inspections.
- This information comes to you with compliments of Valiant Exteriors in Calgary. Contact us if you would like to speak to professional roofers who attend to every job personally.
More Information
Pros and Cons of Pitched & Flat Roofs