Flat Roof Drainage for Dummies

Flat Roof Drain

Insatiable curiosity is a good thing (unless, perhaps, you happen to be a cat). It's one of the reasons people grow up to be problem-solvers like scientists, doctors, architects, and the like. The usefulness of curiosity for self-styled "professional writers" like eHow.com's Jessica Reed is a little more murky, especially when they're attempting to answer questions posed by curious people, Questions like "How Does Water Run Off a Flat Roof,¹ which Jessica attacked for the mother lode of misinformation.

Reed's unfamiliarity with building design in general and roofs in particular is quickly exposed in her first paragraph:

"A flat roof is commonly used on many buildings, especially those that house businesses. Slanted roofs are typically only seen on homes, and are considered more of a decoration. However, a flat roof creates many challenges for the owner. The main problem is in the area of rainfall. Water has to run off of the roof to keep it from leaking down through the ceiling and into the building below. But while water can easily run off a slanted roof, a flat roof impedes the process. It is important to find a way to get rid of the water before it does any damage to the building."

OK, nominally true though "those that house businesses" is rather simplistic: do you consider an apartment complex a "business"? Let's just say, "commercial buildings," Jessica... and then there's the construction of "a flat roof impedes the process"; a rather strange way to say what she means.

Reed then wastes a paragraph on "What can cause a flat roof to leak?" before getting to the meat of the matter, "How does water run off a flat roof?" That's where she explains that "several steps can be taken":

"First, consider having a coating applied that can help keep leaks from occurring. Adhesives are available that can help trap the water out. The main way water can run off a flat roof is through a drain system. Having drains and gutters installed correctly will direct the water into the drains, which will in turn let the water pour harmlessly onto the ground below. Water can also be drained by having the roof built up slightly, to allow it to drain better. A combination of these alternatives allows water to run easily off of the roof."

The stupidity inherent in that paragraph is amazing. For one, all roofs have "coatings" to prevent leaks: slates, tiles, shingles, and the like. Second, you don't put gutters on flat roofs -- what would be the point? Jessica does brush up against truth with her "steps": flat roofs aren't completely flat, and a properly-designed roof will include internal drainage. Do note that these drains won't "let the water pour harmlessly onto the ground below," roof water runs through pipes in the walls. Most flat roofs also have outlets called "scuppers" (a nautical term) to allow water near the edges to drain, usually through a drainpipe that directs the water away from the foundation.

Typical of eHowians, Reed conflated some information she harvested from the web about flat roofs with information about conventional, pitched roofs, to create a mashup of misinformation. When we see that sort of foolishness, we almost always see the fingerprints of Demand Media somewhere -- and we almost always name someone (in this case, Jessica) a Dumbass of the Day.

¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was   ehow.com/how-does_4673241_water-run-off-flat-roof.html

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