Pitch Pockets at Roof Penetrations

Importance of pitch pockets at roof penetrations

Pitch pockets are commonly used in commercial roofs and in residential roofs where the roofs are flat or low slope.   Where a pipe, cable or wire penetrates through a roof membrane, It must be sealed in a specific way to prevent leakage. We often find that mechanical or electrical contractors are not familiar with proper requirements and practices for installation of their materials and equipment through rooftops, but nonetheless building owners should be aware that it’s extremely important to seal these items properly when they pass through the roof membrane.  Except for reroofing circumstances, these items are generally installed after the roof membrane is installed and it’s therefore important to shave the mechanical or electrical work coordinate these elements so that penetrations through the roof can be sealed at the time of installation of the mechanical equipment or electrical equipment.

Sealing Equipment Penetrations With Pitch Pockets

The picture below shows an example of a pitch pocket which seals the penetration of a schedule 40 steel screwpipe gas line through a low-slope TPO roof membrane. The same pitch pocket also seals the power cable and the thermostatic control wiring.   Because these smaller diameter and different shape elements are also installed at the same location, the nature of a pitch pocket is extremely helpful. A pitch pocket, as it works as a tray to contain and restrain a liquid applied sealant, allows the liquid sealant to seal a variety of different shapes of elements.  (Pitch pockets can be so effective in this way, that one of the only viable alternatives available is the installation of a gooseneck type sleeve.)

pitch pocket with seals

The picture below shows the same pitch pocket, more closely.   A pourable sealant has been applied to fill the top of the pitch pocket and surround the elements which pass through the rooftop penetration. The pitch pocket itself essentially forms a tray that will retain this liquid application of sealant so that it can the applied in a way where it surrounds the pipe and all other elements. Some of these elements are relatively small and simply applying gun applied sealant  at the penetration of those smaller elements would be insufficient and would not be self supporting and avoid damage or deterioration over time.   Overtime because of thermal expansion and many other conditions, such as vibration, the pipes and wires and other elements will move differently away from and against the roof membrane.  A pitch pocket seals between those disparate elements to seal in a unique way.

pitch pocket with sealant

In the next picture below you can see that there are a total of four different types of elements that are provided to or conveyed from and away from the packaged heating and air conditioning system. This type of HVAC unit is similar to split systems but happens to be an all-in-one unit that provides both heat and cooling and includes the fan which pressurizes the ductwork as well. All-in-one units like this can be installed on a curb or installed on steel beams that span the building from side to side and bare on the parapet walls. The parapet walls, in the case of most rowhomes and row buildings, provide a structural path at the shortest principle span in the building.  (The rear ell and circumstances of corner bracing may be exceptions and actually provide shorter spans, but these areas are often less centrally located and therefore not conducive to air distribution.)

hvac on roof

In the next picture below, you can clearly see the elements that are sealed by this pitch pocket: the oxidized metal pipe is a gas line, the larger wire is the power cable, and the thinner wire is the thermostatic control cable.

pitch pocket sealing hvac elements

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

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