Hard Piped Rooftop Raceway Installation Tips
If look back at our past blogs, you will see several instances where we find wiring run across the rooftops. It’s very common. The wiring can be used to power HVAC units, other types of mechanical equipment. In some cases power is needed for exhaust fans, and other types of wiring can even be used to install control wiring or solar panel electricity runs. Often, this wiring is just dangled along the surface of the roof. Normally, type NM wiring is used for power, in residential installations.
Often people refer to this type of wiring as Romex, but that’s really a brand name. Its not a name of the actual type of wiring. That type of wiring is not intended to be installed along a rooftop. It’s also not intended to be installed just dangled about like an extension cord. It’s actually required, by the building code, to mount the wiring at specific increments, depending on the type of installation. It’s also required by the building code that the wiring not be installed in a locations where it’s exposed to excessive amounts of UV.
The ultraviolet rays present in typical sunlight can significantly accelerate the deterioration of the cabling sheathing or jacketing and the conductor insulation around each of the wires. Once this protective barrier is deteriorated, it can lead to failure of the power to the electrical equipmen. It can also lead to dangerous situations that could potentially result in a fire.
If you had an HVAC contract or a mechanical contractor or someone installing wiring like this on top of your roof, we recommend at least covering it with something else in addition to the integral jacket of the cabling. In other words, something can be applied on top of that cabling to protect it but whatever is applied should at least be something that can have a high degree of UV resistance. The building code sets limitations.
The picture below shows installation of an EMT, type of conduit used to run electrical wiring. This type of installation is much better exposed NM wiring, for many reasons.
They’ve used junction boxes to make connections, and the conduit mates to the preformed knockouts at the sides of the junction box. The typical roof has a relatively high resistance to ultraviolet, many materials though used for other types of installations on rooftops lack that inherent resistance.
There’s a an oxidized length of C-channel laid on top of a part of the conduits in the area shown the picture below. The placement of this iron channel is just a random occurrence. It’s not actually part of an installation. The c-channel in this case is in part of the electrical system or anything else. In fact it’s likely that this c-channel was used for the HVAC equipment but left discarded alongside of the installation. Rooftops like this low slope roof often have different types of equipment on the roof to service the interior of the building below.
The next picture below shows another junction box that is part of this electrical system. This particular junction box is only connected to one of the conduits. For some reason the electrical contractor left one of the two conduits disconnected from the box. It’s likely that this portion of the electrical run has been abandoned and or is not currently in use.
The next picture shows a junction box with a missing cover. Here the electrical connections and a portion of the wiring of the conductors are exposed. Junction boxes like this should always have a cover mounted and secured in place. Even though the majority of the electrical system on this rooftop is protected from UV, this portion of the cables is exposed. It’s exposed both to UV and to water from typical precipitation just like the rest of the roof. The roof is made to handle that precipitation though, but electrical systems are not made to be residually wet.
The next picture below shows the low slope roof parapet and a pull box used to access the wiring to pull it through around the bend of the conduit run.
In the next picture below you can see two different things. The electrical conduit is secure to the roof with a mounting clamp and a grounding and or bonding wire passes through the same area. Often, in commercial roofs, a lighting protection system will be used to protect the building from the damage associated with lightning strikes.
Clamps, when mounted in a horizontal position, like this, are often problematic in low slope roofs. Low slope roofs should not have any exposed fasteners in a horizontal or near horizontal position. Here, the screw used to fasten the clamp to the structure runs down through a horizontal portion of the low slope modified bitumen membrane. These areas, of fasteners in a horizontal position, should at least be overlaid with a high-performance sealant. We recommend an even better approach though to avoid installation of fasteners through the low slope portions of the roof, by simply installing or mounting the conduit and or cabling at locations in a vertical position.
We provide this information here on our blog, and our website, to help our customers and future clients, and we recommend every building owner in DC who values the longevity of their roof (and their investments) and building use a contractor who values the simple and important principles of proper roof construction like Dupont Roofing DC. Our company specializes in flat roofing here in Washington DC and we’re happy to help building owners of almost all types.
Learn more about our company and the proper techniques of working with roofing on historic buildings in Washington DC here on our blog at DupontRoofingDC.com, and you can call us at (202) 840-8698 and email us at dupontroofingdc@gmail.com. We are happy to help and at least talk through options.
