When it comes to commercial roofing, “flat” is a bit of a misnomer because no roof is perfectly flat. The industry’s standard definition of a flat roof is one that rises a maximum of three inches for every twelve inches of horizontal run. Most commercial roofs have a pitch of less than that, whereas most residential, shingled roofs have a steeper pitch.
Some amount of slope on a “flat” roof is necessary to ensure that water can flow off it. Here’s why that’s important: a 400 square foot area (only 20’ x 20’) of 1-inch-deep water would add 2,000 pounds – 1 ton – of weight to your roof. That amount of water – or potentially more, depending on how much “un-sloped” roof area you have – could create major issues that could severely damage your roofing system and the structure beneath.
Standing water can also increase the likelihood of leaks. Water that’s moving across a roof that’s sufficiently sloped won’t easily seep into tiny openings in the roof membrane. But standing water applies enough downward pressure on the membrane to penetrate those weaknesses and create leaks. Prolonged standing water can also create stress on the seams between membrane sections and other transition points, again creating the potential for leaks.
In addition to potential structural problems, standing water can foster the growth of algae and bacteria that can deteriorate the roof surface. Plus, standing water can contribute to the breakdown of the roof surface because it intensifies sunlight.
Commercial roofs are typically served by one or more of these systems:
- Interior drains on the rooftop channel water down through pipes in the building, then into a sewer or out of the building at ground level.
- Scuppers are openings through a roof’s parapet. Flowing water runs through the scupper and typically into a downspout that carries it away from the building at the ground.
- Commercial gutters, designed to handle a high volume of water, also have downspouts attached to direct water away from the building.
If you’re faced with rooftop drainage problems that you can’t handle yourself, please give the experts at Diversified Services a call.