Phone answered 24/7 · Detroit, MI and nearby communities

Call 24/7: (313) 766-2970
Belle Isle Dry-Out ProsWater Damage Help · Detroit, MI

Why Is My Commercial Building Roof Leaking From HVAC Units?

Last updated October 25, 2026

Call Now (313) 766-2970

The short answer

Common Causes of HVAC Roof Leaks

A leaking HVAC unit on your commercial roof often traces back to a blocked condensate drain line. Debris, algae, or dust can clog the line, causing water to back up and spill over the pan. Over time, the overflow finds its way through roof seams or around the unit's curb.

Another frequent culprit is a cracked or rusted drain pan. Constant exposure to moisture and temperature swings weakens the metal or plastic. Once a crack forms, water drips directly onto the roof membrane. Failed gaskets or seals around the unit's base also allow water to migrate underneath the flashing.

How Weather Worsens the Problem

In cold climates, ice can form in the condensate line or on the drain pan, blocking water flow. When the ice melts, a sudden rush of water can overwhelm the pan and leak onto the roof. In warm, humid weather, high humidity increases condensate production, which can expose an already weak drain system.

Frequent freeze-thaw cycles also expand and contract roof materials, opening gaps around the unit. If you manage a building in a region with harsh winters, inspect your roof after heavy snow or rain to catch leaks early. Look for signs of ice buildup or standing water near the unit.

  • Check for standing water or wet spots near the unit base
  • Look for rust or corrosion on the drain pan and condensate lines
  • Inspect the rubber seals and flashing around the unit's curb
  • Clear debris from the drain line and ensure it slopes downward
  • Note any musty odors or damp insulation inside the building below

Steps to Identify the Leak Source

Start by turning off the HVAC unit and allowing it to dry for a few hours. Then, run water through the condensate drain to see if it flows freely. If water backs up, the drain is clogged. Listen for dripping sounds or look for water stains on the ceiling directly beneath the unit.

Examine the roof membrane around the unit for cracks, blisters, or lifting seams. Water may travel along the membrane before dripping inside, so the visible leak point may not be the source. Use a moisture meter if available to trace the path. If you cannot pinpoint the issue, a professional leak detection service can help.

When to Call a Pro for Roof Leak Repair

If you find a clogged drain or minor seal issue, you might clear it yourself. However, structural damage, extensive membrane deterioration, or recurring leaks call for professional help. A local water damage pro can assess the roof and HVAC unit, then recommend the right repair approach.

They can also identify hidden water damage in the roof deck or insulation. Ignoring a leak can lead to mold growth, weakened roofing materials, and costly interior repairs. Acting quickly limits the damage. If you are unsure, a pro's inspection gives you a clear picture of what needs fixing.

Preventive Maintenance to Avoid Future Leaks

Regular maintenance is the right way to prevent HVAC roof leaks. Schedule a roof inspection at least twice a year, ideally before winter and after summer. Have a professional clean the condensate drains, check the pan for corrosion, and reseal any gaps around the unit's base.

Keep the roof clear of leaves, branches, and other debris that can block drains. Trim nearby trees to reduce falling debris. If you notice any signs of wear, address them promptly. In cold climates, winter prep is especially important, so ensure drains are clear before the first freeze.

  • Inspect the roof and HVAC unit after major storms
  • Clean condensate drains and check for proper slope
  • Replace worn gaskets or seals before they fail
  • Apply roof sealant or patch small cracks as soon as you see them
  • Document all maintenance for your records

Need help right now?

Water keeps spreading into floors and walls, so it is worth acting early. Calls are answered 24/7.

Call Now (313) 766-2970

Frequently asked questions

Can I fix an HVAC roof leak myself?

You can clear a clogged condensate drain or replace a worn seal if you are comfortable working on the roof. But if the leak involves the roof membrane, structural damage, or electrical components, hire a professional to avoid making things worse.

How do I know if the leak is from the HVAC unit or the roof?

Look for the leak's location. If water appears directly below the unit or drips from the unit's base, it is likely HVAC-related. If the leak is elsewhere on the ceiling, the roof membrane might be the issue. Trace water stains and check for cracks or gaps around the unit.

Will my insurance cover HVAC roof leak damage?

Policies vary, and your insurer decides what is covered. Some policies cover sudden, accidental damage, while gradual wear or lack of maintenance may be excluded. Review your policy and document the damage with photos. If in doubt, contact your insurance company to discuss your specific situation.

Call Now (313) 766-2970