Why Commercial Buildings often use Flat Roof Scuppers – PART II

In our last article, we began an explanation on why commercial buildings require scuppers.  In many cases, downspouts and rear collections through a typical residential gutter do not work because of the scale and size of most commercial buildings.

We looked at the details of the building shown in the picture below, in the previous article. You can see, just by glancing at this picture below, that it’s a very large building.  There are interesting similarities though between a large commercial building like this and a typical residential historic rowhome such as those in Washington DC and Capitol Hill.

historic rowhome

Here in the next picture below you can see the area of pointing repair a little bit more closely. The mortar is so deteriorated at the other areas of the wall that it is consistently recessed and the new mortar right around the area of the downspout stands out so much more than the old motor because it is of both a slightly lighter color, but also closer to the flush edge of the brick face.

brick face

The picture below is a collage of two different pictures of different parts of the same downspout area. This picture is a little bit closer than the pictures above and here you can see the area of pointing more clearly, the original brick building was probably built with a typical historic flush joint and not a raked joint, yet the remaining mortar where it has not been repointed has a recess. It’s very likely that the rainwater was diverted through these downspouts but had leakage somewhere at the interconnection of the pathway between the roof and the downspout in the past and that water leaked out of the downspouts and ran down around that area causing more damage and leakage into the interior of the building.

historic flush

The next picture below shows a different commercial building in a densely populated urban lartnof the area. The building also has scuppers, you can see the scupper holes through the parapet, just below the top of the exterior wall.  Just like the scuppers at the building above, those roof scuppers are intended to relieve water, but there’s one big difference. The pictures of the building above all show a collection box, also known as a conductor head. and a downspout.

In contrast, the building in the picture below has no downspouts. Both buildings actually have internal drains that collect in the middle of the rooftop area and then run in drain pipework through the building down to an internal drain system and then out to the public sewer system.   The big difference is that the building in the picture below does not actually use the scuppers during typical water drainage. Those scuppers only become active if the internal drains are clogged or backed up to a point that they cannot handle the flow of rainwater. In fact, those scupper are actually set above the low point of the roof slope.   The other buildings scuppers are built so that they are in the flow or pathway of the low water gravity drain as a part of the roof that drains every time there is significant rain.

The scuppers at this building are intended only as an emergency overflow.  They are analogous to the overflow hole in the back of a bathroom vanity sink.  They are only needed when the regular drains are clogeed so badly that water builds up so much, in this case the water will flow out of these holes instead of filling up all the watly to the rim of the parapet. 

flat roof scuppers

In the cases of both of these buildings, the reason that these buildings have scuppers is because the layout for just a single termination point such as a rear termination as you would see in a residential rowhome, is not a practical option.  These commercial building footprints are so large that the volume of water that would be run in one single point of drain would be so large that it would require massive piping and collection systems.  Internal drains alone could be the solution, but scuppers are actually cheaper than internal drains. Especially in tall buildings such as these commercial buildings, it’s very expensive to run internal drains. Internal drain piping has a different set of standards that require the plumbing to be done at a higher level than just external downspouts. Also, internal drains take up space from the valuable square footage on the internal part of a building.

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, contact us or 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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