How To Prevent Flat Roof Damage When Your HVAC Needs Service

You have your own facilities crew well trained to prevent damage to your low-slope roof. They stay on the walkways, tread carefully, and log their work in a rooftop access record book. But what about third parties? What about preventing damage to your roof from heating, ventilation and air conditioning (HVAC) service workers?

Installing a Rooftop HVAC Unit

Every trade has its skills, tools, and training. Unfortunately HVAC service workers are not deeply trained in respecting a flat roof. Their focus is, naturally, on getting your bulky, heavy, awkward HVAC unit secured, wired, and plumbed. 

If their work boots, the unit itself, and the installation placement interfere with the optimum performance of the roof, do not expect your HVAC company to care or do much about it. You cannot hope an HVAC service worker will know how to repair a torn single-ply membrane, just as you would not expect your commercial roofer to know how to service an HVAC unit. 

Installation is the time of greatest threat to your roof. An HVAC unit added to an existing flat roof (or, more properly, a low-slope roof) requires the HVAC installers to check that the cooling system’s parts do not interfere with the rest of the roof features:

  • Drainage
  • Electrical installation
  • Slope

The sheer weight of the HVAC unit can alter drainage patterns and channels on the roof. Water ponding will result, leading to a rising risk of water leaks, open seams, or even growth of vegetation.

The HVAC curb (the piece on which the HVAC unit sits) is a major risk for water infiltration. If not properly seated, if not properly sealed, the joint between HVAC curb and roof will leak. That intersection must be flashed and sealed correctly the first time. 

Most water leaks from HVAC curbs do not immediately appear inside the building. Instead, the water saturates insulation, runs laterally between roofing material layers, and slowly seeps inside. Indoor humidity levels (one of the areas the HVAC system is meant to improve) rise from the accumulating water. 


Unfortunately, a water leak from the HVAC curb can be confused with condensation issues created by the function of the HVAC equipment itself. The units are designed to vaporize accumulated condensate so it escapes into the outside air. That is the ideal which is seldom the reality. A malfunctioning HVAC unit can cause condensate to pond around the unit on the roof. 

How can your facilities crew tell the difference between condensate pooling and ponding on the roof, around the HVAC unit, and water ponding from depressions or blocked drainage? They can’t. Not even your HVAC service workers or commercial roofers can tell the difference between water and … well, water. 

One tip: track the weather for several days. If no precipitation has fallen for three to four days and a rooftop inspection shows water ponding only by the HVAC unit, condensate is probably the source. Call your HVAC contractor. 

If, though, rain fell two or three days ago and your roof shows several areas of ponding unrelated to the HVAC unit, you have an insulation and slope problem. Call your local, trustworthy commercial roofer.

HVAC Repair and Maintenance

Annual inspection, maintenance, and repair is not just a good idea for a flat roof. HVAC contractors will also encourage you to have your rooftop units checked out periodically. Unfortunately, the same HVAC service workers who had little respect for the roof at installation will be the ones repairing and maintaining the unit. 

Consider all the enemies of your roof when third parties work on it:

  • Tools
  • Work boots
  • Rolling equipment
  • Detached parts

A falling screwdriver can puncture the roof membrane. HVAC service workers can slip and fall (not enough to harm themselves, fortunately, but certainly enough to damage the roof). Even just dislodging ballast can reduce water resistance. Heavy walking, or walking on areas not meant for foot traffic, can cause damaging friction.  


To be blunt, your roof is far more valuable than an hour’s time from your HVAC contractor. So, even if your contractor tacks on an additional hour of service time for working more deliberately, safely, and carefully, the investment is worthwhile. 

Make your requirements plain:

  • Expect HVAC service workers to stay on rooftop walkways
  • Expect them to be aware of the risks to the roof from their boots, tools, and parts
  • Provide protective tarps to minimize surface damage
  • Log the number of workers, their location, and their time on the roof
  • Task a facilities worker to safeguard the roof by monitoring and advising the HVAC crew

PSI Roofing in Oakland Park, Florida is your local, reliable partner in low-slope roofing. We are prepared to repair, maintain, and replace your flat roof using the latest technologies and best practices. Contact us today and we can help prevent third-party damage right away.