A commercial roof leak can quickly turn into a major headache, leading to costly interior damage, operational disruptions, and safety hazards. Prompt and effective repair is essential. While complex commercial roof repairs often require professional help, understanding the common leak sources and basic repair steps can help you respond quickly and communicate effectively with your roofing contractor. This guide focuses on typical commercial flat roof systems in the U.S.

Identify leak source: Visual & infrared inspection

Finding the exact source of a leak on a large commercial flat roof can be challenging, as water can travel far from its entry point.

• Interior Observation: Start by noting the location of the interior leak (stains, drips). This gives you a general area to focus on.

• Exterior Visual Inspection: On the roof, meticulously inspect the area directly above the interior leak, then expand your search outward. Look for:

  • Cracks, punctures, or tears in the membrane.

  • Damaged or lifted seams.

  • Compromised flashing around penetrations (HVAC units, pipes, vents, skylights).

  • Clogged or damaged drains/scuppers.

  • Ponding water (areas where water collects and doesn't drain).

  • Blisters or soft spots in the membrane, indicating trapped moisture.

• Infrared Inspection (Professional Tool): For elusive leaks, professional commercial roofers often use infrared thermography. This technology detects temperature differences caused by trapped moisture within the roof system, accurately pinpointing the leak's origin without destructive testing. This is highly recommended for persistent or hidden leaks.

Clean and prepare the area (remove debris, dry surface)

Proper surface preparation is crucial for a lasting repair.

1. Clear Debris: Remove all loose gravel, dirt, leaves, and other debris from the suspected leak area. Use a broom or a leaf blower.

2. Clean Surface: For TPO, EPDM, PVC, or modified bitumen roofs, clean the area thoroughly with a non-abrasive cleaner (often just soap and water or manufacturer-recommended cleaner) and a stiff brush. Ensure all dirt, grease, and oxidation are removed.

3. Dry Completely: The surface MUST be completely dry for any repair material to adhere properly. Use rags, a heat gun (carefully, on low settings), or allow ample time for air drying. Any trapped moisture beneath the repair will cause it to fail.

Common leak sources: Seams, flashing, penetrations, drains

Most commercial roof leaks originate from these vulnerable points:

• Seams: The joints where membrane sheets are joined. These can separate due to thermal expansion/contraction, poor adhesion, or aging.

• Flashing: The material used to seal the roof membrane to vertical surfaces like parapet walls, skylights, or equipment curbs. Improperly installed or deteriorated flashing is a very common leak source.

• Penetrations: Any element that pierces the roof membrane (pipes, vents, HVAC conduits, drains). The seal around these points can fail over time.

• Drains/Scuppers: Clogged drains lead to ponding water, which can stress the membrane and cause leaks. Damaged drain flanges or connections are also culprits.

• Punctures/Tears: Accidental damage from foot traffic, falling debris, or equipment.

Apply proper repair materials: Primers, sealants, patches

The repair method and materials depend on your roof system type:

TPO/PVC (Thermoplastic):

• Repair: Typically hot-air weld patches of new TPO/PVC membrane over the cleaned and prepped area.

• Materials: Manufacturer-specific TPO/PVC patches, hot-air welding tool, roller, cleaner.

EPDM (Rubber):

• Repair: Apply self-adhering EPDM patch tape or a liquid EPDM sealant over the cleaned, primed area.

• Materials: EPDM primer, EPDM seam tape or patch, roller.

Modified Bitumen:

• Repair: Often involves torch-applying (professional only) or using self-adhering modified bitumen patches. Liquid asphaltic cement or specialized sealants can also be used for small cracks.

• Materials: Modified bitumen patch, torch (for torch-down), cold-process adhesive, sealant.

Metal Roofs:

• Repair: For small holes or worn seams, use a high-quality, elastomeric roof sealant (e.g., silicone, urethane-based) with a reinforcing fabric embedded. For larger holes, a metal patch mechanically fastened and sealed.

• Materials: Metal patch, self-tapping screws, elastomeric sealant, reinforcing fabric.

Reinforce seams & flashing with membrane or tape

These areas are critical for waterproofing:

• Seams: If a seam is lifting, clean thoroughly, apply appropriate primer, and re-adhere with manufacturer-specific adhesive or hot-air welding. Reinforce with a wider strip of compatible membrane or seam tape.

• Flashing: Ensure flashing is securely adhered to both the roof membrane and the vertical surface. Re-adhere any loose flashing, apply new sealant around the edges, and for severe damage, replace the flashing entirely. Use transition details appropriate for the roof system.

Test repair: Water hose inspection, monitor

After the repair dries and cures (follow manufacturer's recommended times):

• Water Hose Test: Carefully run a water hose over the repaired area (and uphill from it) for 15-30 minutes, mimicking rain. Have someone inside check for leaks.

• Monitor: Continue to monitor the area, especially during the next few rain events.

• Professional Review: If the leak persists, it indicates the source was not correctly identified or the repair was not successful.

When to call in professionals

While minor, easily accessible leaks can sometimes be temporarily patched, it's always best to call a professional commercial roofing contractor if:

• Leak Source is Unclear: You can't find where the water is coming from.

• Widespread Damage: The leak is part of a larger problem (e.g., extensive membrane deterioration, multiple leaks).

• Difficult Access: The leak is in a hard-to-reach or unsafe area.

• Specialized Materials: Your roof system requires specialized tools or knowledge (e.g., hot-air welding for TPO/PVC, torch-down modified bitumen).

• Warranty Concerns: Improper DIY repairs can void existing manufacturer warranties.

• Safety Concerns: Working on a commercial roof can be dangerous. Professionals have the training and equipment.

• Persistent Leaks: If your DIY efforts don't resolve the issue, it's time for expert intervention.

Prompt, professional attention to commercial roof leaks saves money in the long run by preventing extensive interior damage and prolonging the life of your roof.

Don't let a small leak become a huge problem! For expert commercial roof leak repair and comprehensive inspections, contact Masterpiece Roofing, your trusted U.S. commercial roofing specialists, today!