Drainage on Low-Slope Commercial Roofs

Positive water flow is an important design element of any flat or low-slope commercial roof. If you own or manage a typical commercial facility, it was likely constructed with one or more means of getting water off the rooftop, because standing water that doesn’t dissipate or drain quickly can cause serious problems.

There are three primary methods for commercial roof drainage, and, depending on its construction – including any additions over the years – your building may use one or more of them:

  • Interior drains. These are positioned in the interior of the roof surface. The design of the roof should include appropriate sloping so that water doesn’t accumulate but flows freely toward a drain. Rooftop drains are connected to a system of pipes that run through the interior of the building to ground level, where water is channeled away from the building. Alternatively, this roof drainage system can empty directly into the sewer system that the building connects to.
  • These openings in a roof’s vertical parapet walls channel rooftop water that is directed to the perimeter, to the outside of the building. Water runs through the scupper and into a collector box that’s mounted on the exterior wall and connected to a downspout that directs the flow to the ground. Again, the roof design should have sufficient slope to enable water to flow freely toward the scuppers.
  • Gutters on commercial facilities that don’t have parapets and scuppers are also common. Because of the roof surface area and volume of water that they must handle, commercial grade gutters tend to be wider than residential. Commercial gutter systems are also connected to downspouts that direct water away from the building and pedestrian areas.

If you and/or your maintenance crew are able to keep rooftop water flowing as necessary by keeping drainage systems clear, make that activity part of your normal building inspection routine. However, if your roof has sagged over time due to age or the weight of ponding water, additional professional help may be required. One fix may include enhancing the roof slope with crickets or tapered insulation to provide positive drainage. This is something an experienced commercial roof contractor should be able to do. More serious situations may require a solution from a structural engineer.

Regardless of your commercial roofing needs, Tusing Builders & Roofing Services stands ready to help. We would welcome the opportunity to serve you.