Commercial Roof Leak Repair in Los Angeles: Diagnosis, Cost, and Same-Day Options

A leak inside a commercial building is rarely just a roof problem. It is a tenant call at 7am, a wet ceiling tile that has to come down before anyone shows up to work, possibly a damaged inventory claim, and a property manager waiting on a real answer about what is going to happen and what it will cost. The good news is that most commercial roof leaks in Los Angeles trace back to four or five repeatable sources, and a competent crew can usually have a tarp on the same day and a permanent fix scoped within 48 hours.

This guide walks through what causes commercial leaks in LA, how the diagnostic process works, what real repairs cost by system, and when patching is throwing money at a roof that needs to come off and be replaced.

The 4 most common commercial leak sources

We pull a leak ticket somewhere in LA most weeks. After thousands of these, the source is almost always one of four things.

1. Penetrations. Every pipe, HVAC curb, conduit, vent, satellite mount, and skylight is a hole in the membrane that depends on a flashing or pitch pan to stay watertight. Pitch pans dry out. HVAC curb flashings get crushed when a tech sets a unit back down crooked. Vent boots crack from UV. The membrane around the penetration is usually fine — the seal at the penetration is what failed. On a 15-year-old commercial roof, penetration failures account for maybe 40% of all leak calls.

2. Seams. Single-ply membranes (TPO, PVC, EPDM) are only as good as the seams. TPO and PVC seams are heat-welded; when an installer ran the welder too cold, too fast, or skipped over a wrinkle, the seam is weak from day one and opens up within 5-10 years. EPDM seams are taped or adhered and naturally have a shorter life than heat-welded seams. Seams fail in linear runs, so the leak inside the building can be 20 feet away from where the seam actually opened.

3. Drains and scuppers. Internal roof drains corrode at the bowl, the clamping ring backs off, the lead flashing collar cracks, the drain strainer disappears under leaf debris and the whole drain backs up into a pond around it. Scuppers (the openings cut through parapet walls) leak at the through-wall flashing where it transitions from horizontal membrane to vertical metal. Drain and scupper failures cause the worst commercial leaks because the water is concentrated where it enters, not spread across the roof.

4. Flashing. Parapet wall coping, base flashing where the membrane terminates against a vertical wall, counter-flashing at the top of the base flashing, and metal flashing on equipment curbs all eventually move, separate, or rust through. Flashing is the transition point between two different materials, and transitions are where most building envelopes fail.

There are other sources — hail damage, foot traffic punctures, blistering from trapped moisture — but if you know the leak is real and the roof is more than 5 years old, the cause is one of these four about 90% of the time.

How we diagnose a commercial leak

A leak source is almost never directly above the interior stain. Water hits the membrane somewhere, runs along the deck, finds a fastener hole or a low spot in the insulation, and drips down inside. Following the stain straight up is how amateur crews patch the wrong spot and have the leak come back the next storm.

Visual walk. Two-person walk of the roof surface with the building manager pointing to where the interior stain is. We photograph every penetration, seam, drain, parapet termination, and equipment curb in that quadrant of the roof. About 60% of leaks are visually obvious from the surface walk: a cracked pitch pan, a torn pipe boot, an open seam, debris damming a drain.

Infrared moisture scan. For larger commercial roofs and leaks that are not obvious from the visual walk, we run an infrared thermal scan after sundown. Wet insulation board holds the day’s heat longer than dry insulation. The IR camera shows wet areas as bright blooms on the thermal image. This maps the saturation footprint inside the roof assembly — important because the leak entry point is typically at the upslope edge of the wet area, not in the middle of it.

Flood test. For ponding sections, parapet terminations, and drain bowls we suspect, we plug the drains, fill the section with a few inches of water, and either watch the interior for the drip to start or use leak-trace dye to confirm the path. A controlled flood test gives a definitive yes/no on whether a specific area of membrane is sound. We do not flood-test in cold weather or on roofs where the deck loading is marginal.

Core sample. When the IR scan shows widespread wet insulation, we pull a 4-inch core through the entire assembly: membrane, insulation board, vapor barrier, deck. The core tells us what the system actually is, how much of the insulation is saturated, and whether the deck has started to corrode (steel) or rot (wood). This is the data that decides whether a repair holds or whether the roof needs to come off.

Diagnosis on an average commercial leak takes 1-3 hours on site. We email a written diagnostic report with photos before the crew leaves.

Emergency tarp vs permanent repair

There is always a question of timing on a commercial leak. If the leak is active and weather is coming in, we tarp first and fix later. If the roof is dry and we have a clear weather window, we go straight to the permanent fix.

Tarp first when:

A storm is forecast within 72 hours and the diagnostic is not finished.
The materials needed for the permanent repair are not in stock and a supplier lead time would push the fix past the next rain.
The leak is into occupied tenant space and the tenant cannot wait for the full repair window.
The damaged area is large enough that the permanent repair will take more than one day.

We use heavy-duty reinforced poly tarps (not the blue residential stuff), anchored with sandbags around the perimeter or screwed-down 2x4 battens for high-wind exposures. Commercial tarping holds through normal LA winter storms — not just a passing drizzle. A typical commercial tarp runs $400 to $1,500 depending on roof size, perimeter conditions, and how many penetrations it has to seal around.

Permanent fix immediately when:

The weather forecast is dry for at least 5-7 days.
The repair scope is under one crew-day.
The membrane and accessories needed are in stock at our shop or available same-day from the local supply house.

Most commercial roof repairs run 1 to 3 crew days from arrival to walk-off. We schedule the permanent fix into the dry window even if we tarped first.

Repair costs by system

Commercial repair pricing in LA depends on the system, the access, the scope, and what the membrane warranty status is (if any). These are the real ranges we are quoting in 2026:

TPO seam re-weld. $20 to $40 per linear foot of seam, with a $400 minimum for the truck roll. A typical 10-foot seam re-weld with adjacent membrane prep runs $400 to $600. Full seam-by-seam survey and weld pass on an aging TPO roof runs $0.50 to $1.50 per square foot of roof area.

TPO patch. $400 to $1,200 for a localized patch (4 to 25 sq ft of patch material with primer, weld, and edge termination). Larger patches scale linearly.

EPDM patch. $300 to $800 for a localized adhered patch with seam primer, splice tape, and edge sealant. EPDM patching is faster than TPO because there is no torch or welder setup time.

Modified bitumen patch. $400 to $1,500 for a torch-applied or cold-adhered patch depending on cap sheet matching and how many plies have to be cut back to find sound substrate.

Built-up (BUR) flashing repair. $500 to $2,000 for a parapet wall or curb flashing rebuild. Built-up flashing repairs involve cutting back the failed flashing, re-flashing with new mod-bit base sheet and cap sheet, and either re-flooding gravel or installing a new cap sheet transition.

Pitch pan re-pour. $250 to $500 per pitch pan including cleanout of failed sealant, primer, and pourable sealer.

Vent boot replacement. $200 to $450 per boot including the new EPDM or molded boot and seal.

Internal drain replacement. $800 to $2,500 per drain including new cast iron or aluminum drain assembly, lead flashing collar, clamping ring, and membrane termination. Replacing a drain typically requires cutting back 18-24 inches of membrane all the way around the drain to install the new flashing collar, then heat-welding or adhering a new ring of membrane.

Scupper rebuild. $600 to $1,800 per scupper including new through-wall sleeve, exterior collector box (if needed), and re-flashed membrane termination.

Emergency tarp. $400 to $1,500 depending on coverage area and anchor method.

These are repair numbers, not re-roof numbers. A full commercial re-roof runs $4 to $12 per square foot installed depending on the system — see our commercial roofing service page for the full breakdown.

When repair will not hold and re-roof is the call

There is a tipping point on every aging commercial roof where another patch is throwing good money after bad. We tell property owners straight when we see it.

Saturated insulation over more than 25% of the roof. Wet insulation never dries out under a sealed membrane. It compresses, loses R-value, holds moisture against the deck, and rots from underneath. Once the IR scan shows widespread saturation, the roof is past the point of repair — the wet insulation has to come out, which means the membrane has to come off.

End-of-life membrane. TPO and EPDM at 25+ years, modified bitumen at 20+ years, built-up at 30+ years. At that age the membrane chemistry is brittle, every seam is suspect, and any patch you add becomes a transition between new flexible material and old rigid material — a built-in failure point.

Multiple active leaks in different areas. One leak is a repair. Three or four leaks in different quadrants of the roof, all at the same time, means the membrane has reached general end-of-life. Patching them individually costs more over 18 months than a re-roof would have cost up front.

Deck damage. If the core sample shows corroded metal deck (more than surface rust) or rotted wood deck, the deck has to be repaired or replaced. That is a tear-off scope, not a repair scope.

Coatings exhausted. If the roof has already been recoated once or twice and the latest coat is breaking down, additional coating is not going to hold. The base membrane has to come off.

Pre-sale or refinance condition. When a property is on the market or up for refinance, a commercial roof with a current 5+ year warranty and a known service life is worth far more than a roof with no warranty and an unknown age. A re-roof during the diligence window often pays back the entire spend in the sale price.

The honest version of this conversation is short: we will tell you when patching makes sense and when it does not. If the math says re-roof, we say re-roof. We would rather walk away from a $2,000 repair than book it on a roof that is going to leak again in six months.

Insurance claim documentation

A commercial roof leak that comes from a covered cause (windstorm, hail, fallen tree, sudden discharge from rooftop equipment) is usually an insurance claim. The adjuster needs three things to settle the claim cleanly:

Date and cause. A storm date with NOAA weather data backing it up, or a service report from the HVAC contractor whose unit caused the membrane damage.
Photographic documentation of the damage. Before-and-after photos from the roof surface, photos of the interior damage, and (for hail) reference photos with a chalk circle or scale next to each impact mark.
Scope of repair with a written estimate. Line-item pricing for the repair scope, broken out by labor and materials, with the membrane system and warranty status documented.

We can put a full claim package together for the adjuster — diagnostic report, photo log, scope with pricing, and proof of license and insurance — at no charge if the work goes to repair through us. For background on how the claim process works in Los Angeles, see our roof insurance claim guide.

A few practical notes: do not let the adjuster’s preferred-vendor estimator low-ball the scope. Commercial repairs on TPO, PVC, and built-up are skilled trade work and the going LA rate is what it is. If the carrier’s estimate misses items, we file a supplemental.

Frequently asked questions

How fast can you respond to a commercial roof leak near me in Los Angeles?

Same day for active leaks during business hours across most of LA County. A truck typically reaches Downtown, Mid-City, Hollywood, Koreatown, the central San Fernando Valley, the Westside, and the South Bay within 60 to 90 minutes. After hours we run a 24/7 emergency line for property managers with active water entering tenant space.

How much does a commercial roof leak repair cost in LA?

Most commercial leak repairs run $400 to $2,500 once you include diagnostic, materials, and labor. Simple penetration repairs and pitch pan re-pours sit at the bottom of that range. Drain replacements, scupper rebuilds, and multi-seam re-welds sit at the top. Larger scopes (full flashing rebuilds, multiple-quadrant repairs) run higher. We quote in writing after the diagnostic walk, not over the phone.

Do you do same-day commercial flat roof repair?

Yes for active leaks. Same-day means we get a tarp on and stop the water entering the building. The permanent repair is scheduled into the next dry weather window, usually within 3-5 days of the initial call. For non-emergency repairs the typical lead time is 5-10 business days from approved estimate to crew on site.

What is the cheapest fix for a leaking commercial flat roof?

Find the actual source and patch it. The cheapest fix is the right fix — chasing leaks with random patches around a stain costs more than one accurate diagnosis. A targeted patch on a single failure point runs $400 to $1,500 for most TPO, EPDM, and mod-bit roofs. Throwing a coating over an unknown leak source is the most expensive non-fix.

Can a commercial flat roof leak be repaired in the rain?

Tarped, yes. Permanently repaired, no. Heat-welded seams, adhered patches, and torch-applied modified bitumen all require a dry, clean substrate. We tarp during the rain to stop active water entry and schedule the permanent repair for the next dry window. Any contractor offering a “permanent fix” while it is raining is selling a patch that will not hold.

What to do right now if your commercial roof is leaking

If water is coming into tenant space, the order of operations is straightforward:

Contain it inside. Buckets, plastic sheeting, and move any inventory out of the drip zone. Pull wet ceiling tile so the water has a path down rather than spreading laterally across the ceiling grid.
Photograph everything. Interior damage, the position of the drip in the room, any rooftop equipment you can see from the ground. Time-stamped photos matter if this goes to insurance.
Call a commercial roofer with same-day capability. Most of the residential roofers in LA do not have the equipment, the membrane material on the truck, or the crew experience to handle commercial single-ply. Make sure whoever you call works on TPO/PVC/EPDM as a regular part of their book, not as a one-off.
Schedule the diagnostic walk and the tarp at the same time. If the same crew is on the roof anyway, they can tarp the suspected area and run the diagnostic in one visit.

For active commercial leaks in Los Angeles, call (818) 446-6122. Same-day response, written diagnostic report, and a real scope with line-item pricing within 48 hours. If you want background reading first, the commercial roofing service page covers the full scope of work we do on commercial buildings, the flat roofing page covers the residential-to-light-commercial flat-roof crossover, and the roof repair service page covers the general repair process on every roof type. For pricing context on the underlying re-roof option if patches will not hold, see the flat roof cost guide and the Downtown LA commercial roofing guide.