Rooftop Commercial HVAC Units

rooftop commercial hvac unit

Many large properties have rooftop commercial HVAC units to power the building’s heating and cooling needs. It’s an important part of an operational building. However, rooftop commercial HVAC units are one of the main causes of roof damage and water leaks. One of the areas we check on during our commercial roof inspections is the mechanical HVAC unit and roof surrounding it.

The five reasons we recommend regular inspections around rooftop commercial HVAC units are:

  1. Failing rooftop commercial HVAC unit flashing
  2. Improper curb-mounted unit installation
  3. Water ponding around unit
  4. Damage to roof membrane due to traffic
  5. Damage to roof membrane from HVAC unit damage


  1. Failing rooftop commercial HVAC unit flashing

Commercial mechanical units are connected to ductwork, electrical, and plumbing into the building’s interior. That means there is an opening in the commercial roof membrane that must be sealed to prevent leaks. Nearly all rooftop units (RTUs) are installed on “curbs”, which allow sturdiness while also allowing the commercial roof to function.

The roof membrane (such at TPO), is installed on the flat roof and up the side walls of the vertical HVAC unit curb. Non-reinforced “flashing-grade” TPO membrane, or uncured EPDM membrane are commonly used for commercial HVAC curb flashing. Flashing a commercial HVAC unit curb using either of these membranes is a highly technical and specialized skillset that should be done under the supervision of a licensed commercial roofing contractor.

  1. Improper curb-mounted commercial unit installation

If the commercial RTU was not installed properly in the first place, it can create an awkward placement that results in a roof leak. For example, if a commercial HVAC unit is installed on a curb that is too short, roof membrane “rubbing” can result and create early roof failure.

Additionally, the sheer weight of the unit (ranging from 500 to 4500 lbs) can create settling of the unit or curb. That settling can affect the roof membrane, potentially causing a tear.

  1. Water ponding around unit

Water ponding on any roof is cause for concern. But when it’s near a commercial HVAC unit it can be extra concerning because of the vulnerability of commercial HVAC unit curbs.

In some cases, condensation from the unit itself contributes to the water ponding. In these cases, installing interior drainage lines to capture the condensation should be considered. It’s also possible to create a cricket on the roof to direct water towards roof drains or gutters.

  1. Damage to the commercial roof due to heavy foot traffic

Commercial HVAC units require a lot of service. Because of the amount of foot traffic needed, the roof membrane around the unit is much more likely to become damaged from the foot traffic. That risk becomes much greater when HVAC technicians bring along their toolsets, as hard objects can be dangerous on commercial flat roofs.

One remedy for heavy traffic around a commercial HVAC unit is to install walkpad membrane, or double layer of roof membrane. This helps reinforce the roof and protect against the heavy traffic.

  1. Damage to roof membrane from HVAC unit damage

Commercial HVAC units are large and heavy. We have seen units damaged by wind which can result in a metal panel blowing off and puncturing the commercial roof membrane. This can cause a large issue as a puncture to a membrane roof is almost certain to result in an interior leak.

We suggest regular commercial HVAC maintenance and inspections to ensure all fasteners are tightly installed to prevent unit panels from blowing off and damaging the roof.

Denver rooftop commercial HVAC unit flashing and roof repair

Assessing commercial unit flashing and the roof membrane around the unit are always included in our commercial roof inspections. Catching issues early with regular maintenance and inspections can result in much more minor (and less expensive) repairs to the RTU or roof membrane.

When you need a commercial roofing team to assess, maintain, or repair your roof around your commercial HVAC unit, contact the team at Sol Vista Roofing.