Why Commercial Buildings often use Flat Roof Scuppers – PART I

Here’s Why Commercial Buildings Use Flat Roof Scuppers

In a recent series of two blog articles we discussed the function of a flat roof scupper and some of the inherent problems related to reversed grade at the drainage inlet.  We also continued that discussion by talking about the parts and components and material types.

Today we will take a look at why commercial roofs often use flat roof scuppers instead of the grade-to-termination type layouts commonly found in residential flat roof buildings.   Although residential and commercial roof buildings generally use very similar types of roof membrane systems, the layout is different. Residential roofs are generally much smaller than commercial roofs.  The most common type of modern roof membrane systems on these buildings are similar, regardless if it is a residential or commercial building, either modified bitumen or TPO or EPDM single-ply type membranes.

Just for a point of comparison, the picture below shows an example of a typical rowhome flat roof rear rain.   This particular rear drain is built in poor form and quality because it does not have a metal rear termination, instead the membrane of modified bitumen roofing just runs over the end of the roof.  The gutter is also clogged and poorly graded to not have proper continuous slope or grade to the downspout outlet. So even though there are many problems in this particular example, this example shows how a rowhome roof can be small and relatively concise enough that it can have grade run in just one direction and to one single point of relief in which all water is intended to drain.

flat roof rear rain

In the next picture below you can see that that gutter is clogged up so much that it has a full channel of water sitting in the gutter.

clogged gutter 1

The next picture below shows a very large commercial building, a very different in configuration and layout, even though the type of membrane used as a roofing system is actually the same.   You can see several details by looking at the photo below. First, the layout of the downspouts seems to be convoluted or complicated or confused. Instead of running the downspouts between the windows, they installed them so that their pathway goes right in front of a lower level window.  You can also see that brick pointing has been done at only the areas around the downspouts. Apparently, those downspouts or the connection between the downspouts and the gutter had significant leakage in the past which channeled and ran concentrated water at the area around the downspouts which led to leakage on the inside of the building because of the need for pointing on the outside of the building. However, in an attempt to only pay for the absolute minimum amount of repairs, the developer or builder chose to only point the brick right at the downspout locations.

large building flat roof scupper

Smart proactive replacement, construction, upkeep and maintenance of low slope roof and mansard roof systems requires an enthusiastic interest and understanding of historical methodologies, waterproofing principles, and building science.   Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building. 

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the roof and related systems of your building in Washington DC, fill out the webform below and drop us a line, it’s quick and easy.  We will be in touch if we can help.

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