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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Commercial Roof
Leak Repair:
Find It, Fix It Once

How to respond in the first hour, trace water to its real entry point, what each repair costs in 2026, and when a coating restoration beats chasing leaks.
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Tell us the roof type, approximate size, building use and where the water shows up inside. We will connect you with a certified applicator near you.

  • Roof type and square footage
  • Where and when it leaks
  • Roof age and warranty status
  • Rooftop units and drains
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5–7%
Share of a building's capital cost that goes to the roof, which still covers 100% of the building and its contents
RCABC Roof Maintenance Guide
48 hrs
Water still on a low-slope roof 48 hours after rain, in drying weather, means the drainage is not doing its job
NRCA, via FRSA
$500–$2,500
Typical cost to re-flash one leaking curb or penetration on a commercial roof
The Roofing Brief, 2026
2x / yr
Minimum inspection frequency, spring and fall, plus after any major storm or rooftop construction
RCABC Roof Maintenance Guide

Commercial roof leak repair goes wrong in a predictable way: someone sees a ceiling tile stain, a roofer patches the closest seam, and the leak comes back with the next storm because the water was getting in thirty feet away at a curb flashing. We manufacture the polyurea, polyurethane and spray foam systems our certified applicators use to repair and restore low-slope and metal roofs, and this guide is how our technical team approaches a leaking commercial roof: what to do in the first hour, how to trace water to its real entry point, what each repair typically costs, when a coating is the right fix and when it is not, and two tools to triage a leak and budget the repair.

Quick answer

Protect people and inventory first, then check whether the roof is under a manufacturer or contractor warranty before anyone cuts or patches it. Most commercial roof leaks come from flashings and penetrations, not the open field, and the drip inside is often far from the hole outside. Have the leak traced (water testing, infrared survey or electronic leak detection), repair the actual entry point with materials compatible with the existing membrane, and replace any wet insulation. If the membrane is aging but the insulation is mostly dry, a full coating restoration can be cheaper than repeated patches; if the insulation is widely saturated or the deck is damaged, plan a recover or replacement.

What's in this guide
  1. 1The first hour of a roof leak
  2. 2Finding the real leak source
  3. 3Leak triage tool
  4. 4Commercial roof leak repair by roof type
  5. 5Repair costs compared
  6. 6Repair, restore or replace estimator
  7. 7When a coating is the repair
  8. 8Stopping the next leak
  9. 9FAQ
Emergency response

The first hour of a commercial roof leak

A leak during business hours is a safety problem before it is a roofing problem. The roof can wait an hour; the people and equipment underneath cannot.

  1. Make the space safe

    Cordon off wet floor, kill power to any fixture or equipment the water is reaching, and pop saturated ceiling tiles with a drain path into a bucket rather than letting them fall.

  2. Protect inventory and equipment

    Poly sheeting over racks, servers and machinery is cheap; damaged contents are usually the costliest part of a commercial leak.

  3. Document everything

    Photograph the drip location with something for scale, note the time, the weather (steady rain, wind direction, snowmelt) and whether HVAC units were running. Mark the drip point on a floor plan. Your insurer and warranty holder will ask for it.

  4. Check the warranty before anyone patches

    If the roof is under a manufacturer warranty, call the warranty holder or the original installer first. Unauthorized repairs with incompatible materials are a common reason warranty claims get denied. Your roof file should name who to call.

  5. Temporary fixes only, then a real diagnosis

    Keep untrained staff off a wet roof. A roofing crew with fall protection can clear a blocked drain or set a temporary patch. Treat that as first aid. The permanent repair comes after the source is confirmed in dry conditions.

Diagnosis

Why the drip is rarely under the hole

On a low-slope roof, water that gets past the membrane runs along the top of the insulation, along the deck flutes or down a fastener until it finds a seam or a gap in the deck. We regularly see the entry point 10 to 40 feet from where it shows up inside. That is why patching the nearest seam so often fails.

The industry rule of thumb, repeated in the RCABC maintenance guide, is that flashings, pitch pans, gravel stops and other roof penetrations are the source of most leaks. In our experience the usual suspects, in rough order, are:

  • Perimeter and wall flashings. Base flashings that have pulled away from parapets, open coping joints, failed counterflashing and termination bars with dried-out sealant.
  • Curbs and penetrations. HVAC curbs, pipe boots, pitch pans that have shrunk away from the pipe, conduit stands and skylight curbs.
  • Drains and scuppers. Loose drain clamping rings, cracked drain bowls, and clogged strainers that turn a drain into a pond.
  • Seams and laps. Unwelded or poorly welded thermoplastic seams, EPDM seam tape that has let go, open laps in modified bitumen.
  • Field damage. Punctures from dropped tools and screws, hail, foot traffic paths to rooftop units, blisters and splits.
  • Things that are not the roof. Masonry walls above the roof line, window systems, coping stones and HVAC condensate lines produce leaks that look exactly like roof leaks. If it drips on a dry day, think condensate, plumbing or condensation first.

How professionals trace a leak

When a visual inspection does not find it, there are four proven methods:

Low cost

Controlled water testing

Isolate one area at a time with a hose, starting low and working up, while someone watches inside. Slow, but it works on any roof and proves which flashing is the source.

Whole roof

Infrared moisture survey

ASTM C1153 covers using infrared imaging to locate wet insulation in built-up and single-ply roofs. Wet insulation holds the day's heat longer and shows up after sunset. Suspect areas are confirmed with core cuts, because not every warm spot is water.

Pinpoint

Electronic leak detection

ASTM D7877 is the guide for electronic methods of locating breaches in waterproof membranes. It pinpoints holes in single-ply and fluid-applied membranes. Black EPDM is semi-conductive and needs a conductive layer under the membrane for valid testing.

Confirm

Core cuts

A small core through the membrane and insulation tells you exactly what is wet, what the layers are, and how many roofs are already on the building. Every core must be patched properly the same day.

Tool 1

Commercial roof leak triage tool

Answer five questions about what you see inside. The tool ranks the most likely entry points using the patterns our applicators see in the field, flags urgency, and suggests the right detection method to ask for. It narrows the search; it does not replace a roof inspection.

Leak source finder

Where is the water most likely getting in?

Scores nine common sources against the drip location, the weather that triggers it, the roof type and the roof's history.

What else is true?
—
Most likely source
—
Urgency

Repair methods

Commercial roof leak repair by roof type

The most important rule: repair with materials compatible with what is already there, prepared the way that manufacturer requires. A patch on a dirty or chalky membrane fails in one season.

Single-ply

TPO and PVC

Leaks show up at seams that were never fully welded, at field-fabricated corners and at punctures. Repairs are heat-welded patches of the same membrane after cleaning, and probing every seam in the area.

Single-ply

EPDM

Seam tape and lap sealant failures, shrinkage pulling flashings off walls, and punctures. Repairs use EPDM primer, seam tape and cover strips. Shrinkage at the perimeter usually means the flashings need to be rebuilt, not caulked.

Asphalt

Built-up and mod bit

Blisters, splits, open laps and alligatored surfaces. Cut out wet or blistered areas, dry in with compatible ply sheets or mod bit, and re-flash penetrations.

Metal

Metal panel roofs

Exposed fasteners with failed washers, open side and end laps, ridge and eave closures, and rust-through. Fastener replacement, lap sealing and seam treatment fix most leaks; see metal roof leak repair.

Foam

Spray foam roofs

Leaks come from punctures, bird pecking and areas where the protective coating has worn through to the foam. Damaged foam is cut out, refilled with foam, and recoated. A worn coating is maintenance, not failure: SPF roofs are designed to be recoated.

Do notSmear roofing cement or a can of rubberized sealant over a TPO, PVC or EPDM roof. It does not bond to those membranes, it hides the real problem, and it makes the proper heat-welded or taped repair harder.
Costs

What commercial roof leak repair costs in 2026

These are typical installed price ranges from 2026 cost guides. Local labor, access (a crane or a tall building adds real money), and what the tech finds once the roof is open move the number. Click a column heading to sort.

RepairTypical costUnitFixesRight call when
Small membrane patch$300–$1,200under 2 sq ftPunctures, small splitsDamage is isolated and insulation is dry
Drain flashing repair$400–$1,800per drainLeaks at drain bowls and ringsLeak appears near a drain
Curb or penetration re-flash$500–$2,500per penetrationHVAC curbs, pipes, pitch pansLeak under or near rooftop equipment
Large membrane patch$1,500–$5,0003–25 sq ftHail, torn areas, cut-out wet spotsWet area is contained
Seam reseal$1,800–$7,50050–200 linear ftOpen laps and seamsSeam failure is local, not roof-wide
Wet insulation replacement$1.50–$2.00per sq ftSaturated insulation under repairsAlways, wherever cores show wet
Coating restoration, flat roof$1.00–$4.00per sq ftWeathered membrane, many small leaksRoof is sound and mostly dry
Metal roof silicone restoration$2.50–$5.00per sq ftFasteners, seams, surface rustPanels are structurally sound
Membrane overlay (recover)$4–$7per sq ftRoof at end of life, dry deckCode allows a recover and wet areas are removed
Sources: The Roofing Brief commercial roof repair guide (2026) for patches, seams, drains, penetrations, wet insulation and overlays; HomeGuide (2026) for flat-roof coating; West Roofing Systems for metal roof silicone restoration.
Tool 2

Repair, restore or replace: budget estimator

Enter what your inspection or moisture survey found. The estimator prices targeted repairs, a full coating restoration and a membrane recover side by side, using the 2026 ranges in the table above, and applies an age-based rule of thumb. Wet insulation is always priced in, because no repair or coating should go over it.

Budget estimator

What will fixing this roof cost?

Repairs = penetrations x $500–$2,500 + drains x $400–$1,800 + seam runs (up to 200 ft each) x $1,800–$7,500 + wet area x $1.50–$2.00. Restoration and recover add $1–$4 or $4–$7 per sq ft of roof.

From an infrared survey or cores
—
Targeted repairs
—
Repairs + coating restoration
—
Membrane recover

Restoration

When a coating is the repair

When a roof has one bad curb, fix the curb. When it has dozens of tired seams, weathered flashings and a new leak every storm, chasing leaks one at a time costs more each year. That is the point where a fluid-applied restoration makes sense: repair the known problems, replace wet insulation, reinforce seams and penetrations, and coat the entire surface as one seamless membrane. The Roof Coatings Manufacturers Association says a properly applied roof coating can extend roof life up to 10 years or more, and most coating systems can be recoated again later.

What has to be true first

  • The insulation is dry, or the wet areas are cut out. A coating over saturated insulation traps the water. Get an infrared survey or cores first.
  • The deck is sound. Rusted-through metal deck or rotted wood around old leaks gets replaced, not coated.
  • The coating bonds. Adhesion is checked on the actual roof. On metal, pull-off adhesion testing under ASTM D4541 is the standard method; on membranes, manufacturers specify their own peel tests.
  • The weather cooperates. RCMA's guidance for water-borne coatings is 50°F and rising, with no rain for the next 24 hours.
  • The product meets a standard. Acrylic roof coatings are specified under ASTM D6083; silicone and moisture-cured polyurethane coatings over spray foam under ASTM D6694 and ASTM D6947. Ask the contractor which one applies.

Where our systems fit, and where they do not

Our certified applicators use spray-applied polyurea such as ArmorSeal 100 AL as a seamless roofing liner over prepared substrates, and ArmorFoam Roof 200 spray foam with UV TopCoat where the building also needs insulation or better drainage. Polyurea cures in seconds, so sections return to service the same day. See our spray foam roofing and flat roof waterproofing pages for how those systems are built.

It is not the right answer for every roof. If an infrared survey shows wet insulation across much of the roof, if the deck is failing, or if the roof is past 20 years with problems everywhere, the money belongs in a recover or replacement. For a single leak on an otherwise healthy roof, a proper spot repair beats coating the whole building. Comparing chemistries? See our roof coating guide and silicone roof coating page.

Leaking commercial roof?

Find the source, fix it once, then protect the whole roof.

A certified ArmorThane applicator can inspect the roof, repair the entry points and quote a seamless restoration if the roof is a good candidate. Tell us the roof type, size and where it leaks.

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Maintenance

Stopping the next leak

Most commercial roof leaks we see were visible from the roof months earlier.

  1. Inspect twice a year and after storms

    Spring and fall, plus after hail, high wind or any rooftop construction. Walk every flashing, curb, drain and seam, and photograph the same spots each time so changes are obvious.

  2. Keep drains and scuppers clear

    Leaves, bird nests and debris turn drains into dams. NRCA's benchmark is no ponding 48 hours after rain in drying conditions. Membrane roofs are designed for at least 1/4 inch per foot of slope under the model codes; water that sits longer points to clogged drains or a sagging deck.

  3. Control who goes on the roof

    HVAC techs, solar installers and sign crews cause a large share of punctures. Keep a roof access log, require walk pads to equipment and inspect after every trade visit.

  4. Keep the roof file

    Warranty, as-built drawings, every inspection report, every repair invoice. When a leak happens, the file tells the tech what the roof is made of and who is responsible for fixing it.

Related guides: flat roof repair for ponding and membrane fixes, metal roof condensation for drips on dry days, ice dam prevention for winter leaks at the eaves, and how to choose roof coating contractors.

FAQ

Commercial roof leak repair questions

How much does commercial roof leak repair cost?

Small membrane patches typically run $300 to $1,200, a leaking curb or penetration $500 to $2,500 each, drain flashing repairs $400 to $1,800, and seam resealing $1,800 to $7,500 for 50 to 200 linear feet, based on 2026 cost guides. Wet insulation found during the repair adds about $1.50 to $2.00 per square foot. Access, building height and what is found under the membrane move the final number.

Why does my roof still leak after it was repaired?

Usually because the repair was made where the water showed up inside, not where it entered. Water travels along insulation and deck flutes before it drips. The second most common reason is an incompatible repair material, such as asphalt roofing cement on a single-ply membrane. Ask for the leak to be traced by water testing, an infrared survey or electronic leak detection before the next repair.

Can a commercial roof be repaired in the rain?

Only temporarily. A crew can clear drains, set an emergency patch or tarp a damaged area to limit interior damage. Permanent repairs need a clean, dry surface so materials bond, so they are done once the roof dries out.

Will a roof repair void my manufacturer warranty?

It can, if the repair is made by someone the manufacturer does not authorize or with materials it does not approve. Check the warranty terms and call the warranty holder or original installer before any work. Many warranties also exclude damage caused by lack of positive drainage.

How do I know if insulation under my roof is wet?

Signs include soft spots underfoot, blistering, and repeated leaks in the same area. An infrared roof moisture survey, done under ASTM C1153 practice, maps likely wet areas at night, and core cuts confirm them. Wet insulation loses insulating value and should be replaced before any repair or coating goes over it.

Should I repair, coat or replace my commercial roof?

Repair when leaks are isolated and the roof is relatively young. Consider a coating restoration when the membrane is weathered and leaking in many small places but the insulation is mostly dry and the deck is sound. Plan a recover or replacement when wet insulation is widespread, the deck is damaged, or the roof is past about 20 years with problems everywhere. Our estimator above compares all three for your roof.

Is my leak from the roof or the HVAC unit?

If it drips on dry days or only while the cooling is running, suspect a clogged or disconnected condensate line, a cracked drain pan or unit panel seams. If it only leaks in rain, look at the curb flashing and the membrane around the unit. Leaks near rooftop units are often a mix of both.

How often should a commercial roof be inspected?

At least twice a year, in spring and fall, and after any major storm or rooftop construction, as the RCABC roof maintenance guide recommends. Keep photos and reports in a roof file so changes are easy to spot and warranty claims are documented.

AT
Written by the ArmorThane technical team. We have manufactured polyurea, polyurethane and spray foam systems since 1989 and support a network of certified applicators who repair and restore commercial roofs. Cost figures are third-party 2026 ranges, not ArmorThane pricing. Updated October 2026.

Sources

  1. RCABC Guarantee Corp., Roof Maintenance Guide: rcabc.org/wp-content/uploads/Roof-Maintenance-Guide-2012.pdf
  2. FRSA, Ponding Water and Manufacturer Warranties (NRCA 48-hour definition): floridaroof.com/Ponding-Water-and-Manufacturer-Warranties
  3. The Roofing Brief, Commercial Roof Repair 2026: Cost and Repair vs. Replace: theroofingbrief.com/commercial-roof-repair-guide
  4. HomeGuide, Roof Coating and Sealing Cost: homeguide.com/costs/roof-coating-or-sealing-cost
  5. West Roofing Systems, Cost to Restore a Commercial Metal Roof: westroofingsystems.com/ballpark-cost-restore-commercial-metal-roof
  6. ASTM C1153, Location of Wet Insulation in Roofing Systems Using Infrared Imaging: astm.org/Standards/C1153
  7. ASTM D7877, Electronic Methods for Detecting and Locating Leaks in Waterproof Membranes: store.astm.org/d7877-14
  8. Carlisle SynTec, SpecTips: Electronic Leak Detection: carlislesyntec.com SpecTips: Electronic Leak Detection
  9. ASTM D4541, Pull-Off Strength of Coatings Using Portable Adhesion Testers: store.astm.org/d4541-22
  10. ASTM D6083, D6694 and D6947 roof coating specifications: store.astm.org/d6083, store.astm.org/d6694, store.astm.org/d6947
  11. Roof Coatings Manufacturers Association, FAQs: roofcoatings.org/faqs
  12. Building Code Trainer, Minimum Roof Slopes by Roofing Material (IRC 2021): buildingcodetrainer.com/minimum-roof-slopes-required-by-roofing-material

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