Flat Roof Parapets And Coping – Part II

Roof parapets and coping – things to look out for

In a recent article we took a look at a roof with an aluminum rooftop parapet coping system.  In this case, the rooftop deck is sheaved or covered with plywood or oriented strand board. That wood, also refer to as decking or sheathing, essentially spans over top of the roof rafters to create the planar flat, field surface of the rooftop deck.

Before we even get into talking about the defects and problems with this installation, it’s probably a good idea to examine some of the anatomy and terminology used to describe roof terminations at a parapet. A parapet is a projecting wall that extends above the rooftop. These parapet walls typically are at the demising center between two distinct properties or at the exterior perimeter of a building. In many cases though, a parapet is not actually required at an exterior wall. The building code does require that the parapet or demising wall between two distinct units extend above the roof for fire separation purposes.   In modern construction using the modern building code, parapet walls must be built with fire resistant rated construction similar to the underlying wall, in most cases.

Some of the defects are problems in installation of the I-beams follow in the list below. 

  1. The I-beams are set on a neoprene isolator, but they have no structural attachment to the rooftop deck.
  2. The connection methodology lacks vibration isolation other than the single neoprene  Separator.
  3. The substrate below the coping has not been made structurally consistent or prepared to support such a load.
  4. The i-beams are uncoated and are already rusting

roof parapets and coping

One question that we get, again and again is whether or not coping is even required by the building code or the requirements in DC through DCRA. The answer is clear, coping is absolutely required on top of parapets. The building code section 705 and 1503 make it very simple, “Parapet walls shall be properly coped”.   This question comes up a lot because most roofing contractors, when they install new roofs, do not install new coping metals on non-commercial properties in Washington DC, when you get up on a rooftop relatively high up and you can often see many of the surrounding roofs, it’s very clear the majority of them do not have parapet coping but it’s also clear that in the building code it’s actually required.  Every time a roofing contractor puts a roof on without new coping, they’re not following the building code. Many items in renovations or existing properties could be considered a grandfather condition, but new roof systems in most cases have almost entirely new elements.   The rooftop coping is not one of the things that should be considered a grandfather condition. In fact unless the client is specifically requesting the contractor to not install the coping, and effort to save money or cut quality and cost the same time, the roofer shouldn’t stall new coping with a new roof or overlay.

roof overlay

A separate but related item regarding installation of mechanical equipment on I-beams or set on rooftop parapet or rooftop curves, is whether or not the clearance provided by the parapet and I-beam assembly is sufficient for access to the mechanical equipment. In most cases, with relatively small mechanical equipment can be sufficiently accessed with just about 8″ of clearance, most parapets are around 8″ above the adjacent rooftop.  In the case of large equipment though, the building code actually requires that more space is provided for access because logically, it makes sense you need to get further under a machine to repair it if it’s a larger or wider machine, to get farther under a machine, it has to be a little bit higher to allow for more clearance from a human body, especially in the thicker parts.  For a lot of the HVAC contractors the middle part of their bodies (torso and abdomen) is disproportionately thicker than the other parts of their body. In fact, Table 1510.10, says that mechanical equipment over 60″ wide in the shortest horizontal dimension should be set at least 48″ above the rooftop deck, in many cases.

The picture below shows a lap joint in the horizontal run of the parapet coping. The coping is facing on the sides which is appropriate and preferred to top fasting. Top fastening of parapet coping should be avoided in all possible circumstances. 

lap joint roof parapet

Joints at coping runs are required to have at least 3″ of overlapping coverage and at least two beads of gun applied sealant applied continuously traversing the coping metals.

roof coping metals

How To Maintain A Modern Roofing System

Smart proactive replacement, construction, upkeep and maintenance of low slope roof systems requires an enthusiastic interest and understanding of 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.  We will be in touch if we can help.

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