Commercial Roof Membrane Types & Repair Methods
The repair method depends entirely on the membrane type. Using the wrong technique or material will cause the repair to fail. Identify your membrane first:
| Membrane | Repair Method | Lifespan | Cost Range |
|---|---|---|---|
| TPO | Hot-air weld patches & seams | 20–30 years | $5–7/sq ft |
| PVC | Hot-air weld (same as TPO) | 20–30 years | $6–9/sq ft |
| EPDM | Adhesive bonding + seam tape | 25–30 years | $4–6/sq ft |
| Built-Up (BUR) | Hot asphalt or cold adhesive + fabric | 20–30 years | $5–8/sq ft |
| Modified Bitumen | Torch-applied or self-adhering patches | 15–20 years | $4–7/sq ft |
Pro Tip
Common Commercial Roof Problems
Ponding Water
Water that remains on the roof 48+ hours after rain. Degrades membranes, adds structural weight (5 lbs/sq ft per inch of water), voids some warranties. Caused by inadequate slope, clogged drains, or structural deflection. Fix: clear drains, add tapered insulation to create slope, or install additional drains.
Seam Failure
The most common commercial roof leak source. Seams separate due to age, poor installation, thermal cycling, or membrane shrinkage. TPO/PVC seams can be re-welded if caught early. EPDM seams can be re-taped. If seam failures are widespread, it indicates the membrane is reaching end-of-life.
Flashing Deterioration
Flashing (where the roof meets walls, curbs, and penetrations) fails before the field membrane because it's under more stress. UV exposure, thermal expansion, and water flow concentrate at flashing details. Re-flashing a parapet wall or HVAC curb is a common repair ($500-2,000 per detail).
Punctures & Impact Damage
HVAC maintenance, foot traffic, dropped tools, and hail all puncture commercial membranes. High-traffic areas should have walk pads. Post signs directing foot traffic to designated paths. After any rooftop work by HVAC, electrical, or other contractors, inspect the membrane for damage immediately.
Blow-Off & Wind Damage
High winds can lift and peel membrane from the roof edges and corners. Perimeter and corner zones experience 2-3x more wind uplift than the field area. Check edge termination details, coping, and parapet flashing after every major storm. Loose or billowing membrane in these areas needs immediate attention.
How to Repair a Commercial Flat Roof
Safety Warning
Commercial roofs require fall protection. OSHA requires guardrails, safety nets, or personal fall arrest systems for work at heights above 6 feet. Never walk on a wet commercial roof — single-ply membranes are extremely slippery when wet. Ensure someone knows you're on the roof and carry a phone.
Locate and document the damage
Walk the entire roof surface in a grid pattern. Check every seam (where membrane sheets overlap), every flashing detail (where the roof meets walls, curbs, and equipment), every penetration (pipes, vents, HVAC units, drains), and the membrane surface itself. Mark damage locations with chalk and photograph everything with a ruler for scale. Note: on large commercial roofs, the leak location inside rarely matches the roof entry point — water can travel 20+ feet along insulation or deck before dripping through.
Determine the repair method
Match the repair to the membrane type: TPO and PVC require heat welding (a hot-air gun at 900-1100°F to fuse membrane sheets together). EPDM uses adhesive bonding (contact cement and primers). Built-up roofing uses hot asphalt or cold-process adhesive with reinforcing fabric. Modified bitumen uses torch-applied or self-adhering patches. Using the wrong method or material will cause the repair to fail — always match the membrane.
Clean and prime the area
The repair area must be clean and dry. Remove all dirt, debris, and loose material. For TPO/PVC: wipe with membrane cleaner to remove oxidation and contamination. For EPDM: apply EPDM primer and let it tack up (5-10 minutes). For BUR: remove gravel from the repair area and clean to bare membrane. Temperature matters — most adhesives and welding require ambient temps above 40°F. Schedule repairs for dry days with 24 hours of clear weather ahead.
Apply the patch or repair
Cut the patch 6 inches larger than the damage on all sides with rounded corners. For TPO/PVC: position the patch and heat-weld all edges using a hot-air welder, maintaining consistent speed and temperature. Test the weld by probing with a blunt tool — it should not separate. For EPDM: apply bonding adhesive to both the patch and the roof surface, wait until tacky, press together firmly, and roll with a J-roller from center outward. For BUR: apply hot or cold adhesive, embed reinforcing fabric, apply another coat, embed a second fabric layer.
Seal, test, and document
Apply lap sealant (caulk-grade) along all patch edges as a secondary water barrier. For seam repairs, apply seam tape or sealant per manufacturer specs. If possible, flood-test the repaired area by damming water around it and leaving it for 24 hours — check inside for any dripping. Take dated photos of the completed repair and add them to the roof maintenance log. Warranty-covered repairs should be documented and reported to the manufacturer.
Your commercial roof repair is complete. Add this repair to your maintenance log and re-inspect in 6 months.
Recommended Products for Commercial Roof Repair
Dicor Self-Leveling Lap Sealant
$8 – $15Professional-grade sealant for seams, flashing, and penetrations. Self-levels for a smooth finish. Works on TPO, EPDM, and most commercial membranes.
- Self-leveling formula
- UV and weather resistant
- Works on all membrane types
- 10-year flexibility
Firestone QuickSeam Splice Tape
$35 – $60EPDM seam repair tape. Peel-and-stick application for fast seam repairs without adhesive or heat. Used by professional EPDM installers.
- No adhesive or heat needed
- Professional-grade bond
- Works in temps above 40°F
- 6-inch width covers seams fully
Gaco GacoFlex Silicone Roof Coating
$120 – $180 (5 gal)100% silicone roof coating for full-roof restoration. Withstands ponding water. Apply over existing membrane to seal and add 10-15 years of life.
- Ponding water safe
- Reflects 80%+ UV
- ~250 sq ft per bucket
- No primer on most membranes
Leister Triac ST Hot Air Welder
$800 – $1,200Professional hot-air welder for TPO and PVC membrane repair. Variable temperature control. The industry-standard tool for commercial thermoplastic roof repair.
- Variable temp 120-1290°F
- Lightweight (1.5 lbs)
- Nozzle attachments included
- Industry standard tool
Commercial Flat Roof Repair Costs
Commercial roof repair costs depend on the membrane type, damage extent, and whether you need a localized repair or full-roof solution:
Commercial Flat Roof Repair Costs (2026)
| Repair Type | DIY Cost | Professional Cost |
|---|---|---|
| Sealant / caulk repair | $20 – $50 | $200 – $500 |
| Patch repair (per patch) | $50 – $150 | $300 – $1,000 |
| Seam / flashing repair | $50 – $200 | $500 – $2,000 |
| Section replacement (per sq ft) | $2 – $4 | $4 – $8 |
| Full roof coating (per sq ft) | $0.75 – $1.50 | $1.50 – $3.50 |
| Full re-roof (per sq ft) | Not recommended | $5 – $12 |
Costs are per repair or per sq ft as noted. Full roof coating and re-roof costs are for a typical 10,000 sq ft commercial roof. Prices vary by membrane type and region.
Pro Tip
Commercial Roof Maintenance Schedule
Proactive maintenance extends commercial roof life by 5-10 years and reduces total lifetime repair costs by 30-50%. Follow this schedule:
| Frequency | Tasks |
|---|---|
| Monthly | Clear drains and scuppers of debris. Check for ponding water after rain. Visual check of membrane from ground level. |
| Quarterly | Walk the roof surface. Check seams in high-stress areas (corners, edges, equipment curbs). Look for punctures from foot traffic or debris. Remove vegetation growth. |
| Twice Yearly | Full inspection: all seams, flashing, penetrations, edge details, and membrane surface. Spring (post-winter) and fall (pre-winter). Repair any issues found. |
| After Storms | Inspect for blow-off damage, hail punctures, and displaced equipment. Check drains for storm debris. Photograph any damage for insurance. |
| Annually | Professional inspection with written report. Core sample if roof is 15+ years old to check insulation moisture. Update maintenance log and plan next year's budget. |
Pro Tip
Repair vs Replacement Decision Guide
Repair / Coat
- ✓ Roof is under 20 years old
- ✓ Damage is localized (under 25% of area)
- ✓ Deck and insulation are dry
- ✓ No structural ponding issues
Full Replacement
- ✗ Roof is over 25 years old with widespread failure
- ✗ Wet insulation (core sample shows moisture)
- ✗ Multiple leaks across different areas
- ✗ Structural deck damage or severe ponding
When to Call a Professional
- Any TPO or PVC repair (requires heat welding equipment and certification)
- Leaks affecting interior operations or inventory
- Roof is under manufacturer warranty (DIY repairs may void it)
- Ponding water that doesn't drain within 48 hours
- Repairs on roofs above 20 feet without fall protection
- Multiple leaks suggesting systemic membrane failure
Related Guides
Frequently Asked Questions
Written by
HomeRepairBase Editorial Team
Our team of home improvement experts and licensed contractors creates detailed repair guides, cost breakdowns, and troubleshooting tips to help homeowners tackle structural issues with confidence.