flat roof maintenance and roof drainage

Your typical large raindrop is around a quarter inch in diameter and, amazingly, falls at 20.2 miles per hour. One raindrop will hardly damage your commercial roof, but multiply that one drop by the millions your flat roof receives every year, and the volume of water—and all those impacts—can degrade your rooftop drainage system. Without flat roof maintenance, including cleaning scuppers and drains, your commercial property’s roof could become a small pond. 

Anatomy of Your Drainage System

For low-slope or flat roofs, two principal devices provide a path for water to drain from the roof. Scuppers are parapet-area drains that connect to exterior downspouts. These lead water away from your building’s foundation. Interior drains are centered or set in from the parapet and, like scuppers, drain water down and away from your building. Secondary scuppers, openings a few inches above the finished roof surface, act as backup drains if the main scuppers get clogged.

Clogs on roofs are common. Both scuppers and interior drains require a strainer to keep debris from falling into the drainpipes or downspouts. These catch a lot of twigs, leaves, branches and natural material (from critters), so consequently they often get clogged themselves. Flat roof maintenance can prevent a small clog from turning into a huge repair bill. When a strainer clogs, water ponds on your roof. Poor drainage can affect not just your roof, but your building foundation. Poor roof drainage can cause interior leaks, too.


The vicious cycle of ponding, especially in buildings with wooden roof decks and joists, can cause a roof to deteriorate. Scuppers or interior drains clog and water backs up. Its weight, even for a shallow pond, is enough to deflect roof deck members or joists below. This sets up the cycle, because now the joists are already deflected and a great catch basin has been formed on your roof. Soon organic matter and seeds will transform your flat roof into a plant nursery.

PSI Roofing’s Remedy

By partnering with PSI Roofing to help with flat roof maintenance on your commercial property’s roof, you know your scuppers and drains will be clear, ponding will never get a start, and the watertight integrity of your roof, from flashing to parapets to ballast, will keep your business dry.

Contact PSI Roofing today to learn how we can help preserve your foundation and prevent roof leaks by keeping your roof drains clear.