Residential Roof Penetrations Cannot Be Used On Commercial Roofs – Part I

See why you should never use residential roof penetrations on commercial setups

Penetrations, through roofs, are essentially holes for things that have to go through a roof membrane or roof system.  Almost all types of both pitch roofs and low slope or flat roofs have penetrations that go through the roof membrane or roof system. These types of penetrations are used for all types of wires, cables, piping, or mounting devices that need to be secured to the rooftop system. pipes, for example, often go through a rooftop system to run refrigerant, water or fuel to rooftop equipment such as HVAC units. 

In some cases, natural gas pipes, for example, will run through the roof system to go to a rooftop HVAC unit. It’s, across the board, better for there to be no penetrations through a roof membrane. Roof membranes work very well in the field areas of the roof, most complications come from the areas of the penetrations through the rooftop system or from the perimeter or termination areas of the roof membrane.

Today, we are specifically taking a closer look at rooftop penetrations related to exhaust air. There are particular ways that are acceptable to terminate and run exhaust air, normally ducted, through a rooftop membrane, but often, especially in parts of Washington DC such as Capitol Hill and other historic neighborhoods where there are flat roofs on residential row homes, we see shortcuts that have been taken by other contractors where they have installed residential type roof materials on flat roofs. Flat roofs are commercial systems, even when installed on rowhomes, and residential roof materials are not acceptable on flat roofs.

The picture below shows an example of a residential roof exhaust termination that has been installed on a flat roof. This type of material is never intended to be installed in a flat roof system and is installed improperly. The building code requires that there is at least several inches of clearance between the bottom of a air exhaust termination and the horizontal field of the roof.

residential roof penetrations exhaust

A wider-angle view of the rooftop follows for context.  You can clearly see the unpainted courses of modified bitumen roof membrane in the photo below.

residential roof exhaust closeup

The next picture below shows an example of the same type of roof exhaust termination but installed as intended on a shingle roof. The aluminum vent termination has an integral flange which is intended to be concentrically laid below shingles and above or over top of courses of roof shingles below the vent. This type of installation does not apply or work in a low slope type roof application.

roof exhaust termination

The easiest and quickest takeaway is that it’s always better to use a contractor who understands the principles of building science and understands the rules related to installation of building materials. The installers of the vent shown in the picture above clearly do not understand the rules regarding proper installation of low slope or flat roof materials.

Maintaining a Flat Roof 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, fill out the webform below and drop us a line.  We will be in touch if we can help.

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