There are three factors that affect proper roof drainage: the slope of the roof, the size of the drains and the placement of the drains (more often referred to as gutters on residential buildings). In addition, it is a good idea to take into account the amount of rainfall landing on the roof, the duration of rain events and the speed the rain collects at the drainage points.
Gutters and drains channel water away from the exterior walls and foundation of your building or home. However, proper gutter maintenance, installation and materials are critical to prevent roof damage. A blocked gutter or roof drain causes water to back up under the roof membrane or pool in places that could take days to dry out. Standing water is never a good thing on any roof surface.
Here are some things to consider when thinking about drainage for your roof:
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Aluminum and steel gutters are the most common choice for gutter material because they are durable and resistant to corrosion, cracking or bending. Corrosion, cracking and bending of gutters are one of the most common causes of damage to roofs.
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The downspouts, which carry the water and small debris away from your home or business have a tendency to clog and back water up onto your roof or around the foundation. Proper maintenance and regular checks of the downspouts and gutters is essential to keep water flowing smoothly away from your building.
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Clogged gutters are one of the most common causes of roof damage. Open-top gutters are a magnet for debris (leaves, sticks, etc.) and can even serve as nesting spaces for birds and squirrels. When a gutter is blocked, water spills over the edge of the gutter. The collecting water soaks and rots the materials of your roof. Standing water and debris in your gutters also makes an ideal home for mold, mildew and algae.
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Make sure the drains and gutters have been properly installed. Improper installation is the main cause for gutter and drain failure. Gutters must be installed with the pitch and angle of the roof in mind. If installed incorrectly, water will flow in front of or behind the gutter, causing damage to your roof line; or the gutters can crack or pull away from the building entirely.
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When deciding where and how many drain or gutters to place, particularly on a commercial building, here is a general guideline. Locate drains no more than 50 feet from the roof perimeter and not more than 100 feet apart.
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Finally, every city and state has local building codes that should be checked before any building, change or addition is made to your structure.
If you suspect your gutters are not functioning properly, the best idea is to call in a professional roofer. They will know not only the drainage rate and building codes for your area, but will also be able to install and maintain your drainage system as well.
