Drainage on Your Commercial Roof

Ensuring that your commercial roof’s drainage system is working as designed is critical to maintaining watertight integrity. A gallon of water weighs about eight pounds and having a pool of undrained water on your rooftop adds stress to the surface and building structure and can significantly shorten the life of your roofing system.

“Flat” commercial roofs are typically not 100% flat – at least they shouldn’t be, because water needs gravity to flow. In fact, a flat – low-slope – commercial roof is usually defined as having a slope or pitch of no more than 3 inches of height for every 12 inches of length. The slope of most flat roofs are actually less than that, but sufficient to allow for good water flow.

A properly designed roof will typically have one of the following 3 types of drainage systems, or a combination: interior drains, scuppers, and gutters.

• Interior drains are placed within the roof area with the surrounding roof deck sloped to enable water to flow freely toward the drains. The drains are connected to pipes that run through the interior of the building before emptying at ground level or directly into the sewer system that serves the building.
• Scuppers are openings in the parapet wall of a roof that water is directed to because of sloping that’s intentionally built into the roof surface. Water runs through the scupper and usually into a device called a collector box that’s mounted on the exterior building wall. The boxes then typically drain into attached downspouts that send the water to ground level and away from the building.
• Gutters on commercial facilities are also commonly used. They are normally wider than those used on residential installations – 6 inches vs. 5 inches – because a commercial roof’s larger surface area produces more water volume and runoff. Commercial gutter systems should also have downspouts attached to direct water away from the building.

If your commercial roof is not draining properly, the pros at Complete Commercial Roofing would welcome the opportunity to evaluate the situation and resolve the issues. Contact us today!