Learn in detail about shingle roof boots on flat roofs
Should You Use Shingle Roof Boots On Flat Roofs?
Again and again, as we are checking low-slope rooftops (aka: flat roofs) in Washington DC, we see a recurring problem where some previous contractor (or homeowner) has installed a shingle type roof boot around a pipe penetration through a flat roof. Shingle roof boots are not intended to be used on flat roofs for a variety of reasons, mainly though because they cannot be sealed properly, alone, to a flat roof membrane. This problem happens to be prolific because some people out there in Washington DC are doing work on flat roofs without following the rules of installation and proper work practices and we see this issue repeatedly and often.
The picture below shows an example of a flat roof in Washington DC, in a series of typical historic row homes. This particular roof happens to be a modified bitumen single-ply roof membrane, one of the most common types of flat roof membranes and one of the better or best of all options. We see clear evidence that TPO membranes and other synthetic type single-ply flat roof membranes perform better, over time, than certain types of historic membrane such as built-up roofs and some metal roofs.
The picture below shows that same roof but looking from the front of the roof towards the back. You can see the HVAC equipment, mounted on steel I-beams above the rooftop. These steel beams are resting on the rooftop parapet. That parapet is an extension of the solid masonry demising walls between this building and the adjacent rowhome.
The HVAC portion of the installation is good in many aspects. The line set to the HVAC unit, containing the refrigerant lines and the thermostat control wiring, is fully insulated and the steel beams are at least coated and not left as just bare steel to oxidize exposed to the elements. These are positive signs.
Shingle Roofs Vs. Flat Roofs
The next picture below shows a close up view of the residential roof boot. This happens to be a residential building, but it’s not a shingle roof. Shingle roots are generally classified as residential roofs and flat roofs like this are generally considered to be commercial roof systems, even though in this case the property happens to be a residential building.
The reason that it’s not acceptable to use a single roof boot for installation on a flat roof membrane is because the base of the boot at the penetration is not properly sealed to the membrane if, as in this case, it is installed by residential means and methods. The edge aluminum base plate of the boot, sitting on top of the rooftop, will delaminate from the surface of the substrate membrane. That plate, shown in this picture happens to be covered with a smeared on application of asphaltic sealant, but that asphaltic sealant is not a permanent installation. It’s only intended for short term or redundant applications where the actual opening is covered in a concentric manner.
As a context of comparison, the next picture below shows an example of a plumbing vent that was installed in the modified bitumen roof at the same time of installation of the single-ply roof membrane. This particular penetration happens to be created or set with compatible modified bitumen materials in a concentric lap which is technically appropriate for a commercial roof penetration.
Maintainance Of Low Slope Roof Systems
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.