Flat Roof Repair in Austin: Finding the Leak on TPO, Mod-Bit and Built-Up Roofs
A leaking flat roof can usually be repaired if the leak is found at its real source and the insulation under it is still dry. The catch is that on a flat roof, the water often doesn't come in where the stain is. A good repair starts with tracing the water back to the opening, checking how far it spread, and then fixing the membrane, flashing or drain that let it in.
Vantage Roofing repairs flat and low-slope roofs on homes and small commercial buildings around Austin, Round Rock and Pflugerville. Here's how the leak gets found and fixed.
Why is my flat roof leaking somewhere other than where the stain is?
A flat roof is layers: the membrane on top, then a cover board or insulation, then the deck. When water gets through the membrane at a seam, a pipe, a curb or a drain, it can run sideways through the insulation or along the ribs of a metal deck before it drops through. Old patches can also send water in a new direction instead of stopping it.
So a patch right above the drip can miss the real opening. Start the search uphill from the stain and work outward.
Where do flat roofs usually leak?
On the flat roofs we inspect around Austin, these are the spots we check first:
Seams where two sheets of membrane meet, especially at corners and laps that were patched before.
Flashing at walls and parapets, where the membrane turns up the wall and the top edge can pull loose or crack.
Pipes, vents and curbs for rooftop AC units, where sealant dries out and boots split.
Drains and scuppers, where debris backs water up and the membrane around the drain gets the hardest wear.
Punctures from foot traffic, dropped tools, hail or service work on rooftop equipment.
AC condensate lines that dump water on the roof all summer and can keep one spot wet.
How do roofers find a leak on a flat roof?
Here's how a flat roof leak inspection usually goes:
Map it from inside. Mark where the stains and drips are and when they show up: every rain, only hard rain, or only when the AC runs.
Walk the roof. Look uphill from each stain for open seams, split flashing, loose edges, clogged drains and old patches. Soft or spongy spots can mean wet insulation underneath.
Check for trapped water. An infrared scan or a moisture meter shows areas that read wetter than the rest. These tools read indirectly, so suspect areas get confirmed with a small core cut.
Test when it's not obvious. For a leak that keeps coming back, electronic leak detection can pinpoint a hole in the membrane, though it doesn't work on every roof.
You should walk away with photos of the problem spots and a plain explanation of what's wrong.
What does the repair look like on TPO, mod-bit and built-up roofs?
TPO and PVC (white single-ply roofs). These are repaired by heat-welding a new piece of membrane over the damage. On an older roof, the surface has to be scrubbed, rinsed, dried and wiped with the manufacturer's cleaner first, or the weld won't hold. Every weld gets probed afterward to make sure there are no gaps. If someone smeared roofing tar or flashing cement on a TPO roof, that area usually can't be welded to and has to be cut out and replaced.
Modified bitumen (mod-bit). Splits, open seams and worn spots get cleaned and patched with compatible membrane. Blisters are a judgment call. An intact blister is generally left alone, and you shouldn't step on it. One that's broken open, cracking around the edge, in a walkway or pulling a seam apart gets cut back to solid, bonded material, any wet insulation underneath is replaced, and the area is patched.
Built-up roofs (tar and gravel). Repairs follow the same idea: clear the gravel, cut out damaged layers to sound material, replace wet insulation, rebuild the plies and put the surfacing back.
On every type, wet insulation has to come out. Patching the membrane over soaked insulation traps the water in the roof.
Is standing water on a flat roof a problem?
The National Roofing Contractors Association treats water that's still sitting more than 48 hours after a rain (in normal drying weather) as ponding. Flat roofs are designed with at least a quarter inch of slope per foot so they drain. Ponding keeps the membrane wet and adds weight the roof was only designed to carry up to a point.
Fixes include clearing drains, adding tapered insulation or a cricket to move the water, and rerouting AC condensate lines. If your roof has parapet walls that can trap water, the building code calls for overflow drains or scuppers so water has a way off when the main drains back up. Ask about it at the inspection.
Repair or replace: when is a flat roof past fixing?
A repair makes sense when the leak is in one spot, the rest of the membrane is in decent shape, and the wet insulation is limited to a small area. Replacement is the honest answer when wet insulation runs through large parts of the roof, seams are failing all over, or the membrane is cracked and worn across the field.
A coating won't stop an active leak; our roof coating guide covers when one makes sense. And if the problem turns out to be a plumbing leak or a sweating duct, not the roof, we'll tell you.
For flat roofs in Austin, the energy code also comes into play. Repairs smaller than half the roof or 2,000 square feet (whichever is less) don't have to meet the cool-roof requirement. Bigger jobs over cooled space do. More on our commercial flat roofing page.
Schedule a flat roof inspection
Call (737) 383-1768 to schedule a free roof inspection. We'll find where the water is coming in, show you photos, and tell you honestly whether it needs a repair, a replacement, or nothing at all. Vantage Roofing backs its work with a 10-year workmanship warranty on full replacements and up to 1 year on service repairs.
Frequently asked questions
Can you come look at my flat roof first before telling me what it needs?
Yes. Vantage Roofing does free roof inspections on flat and low-slope roofs around Austin. We check the seams, flashing, drains and rooftop equipment and look for wet insulation. You get photos and a written estimate, and we'll tell you if it only needs a small repair or nothing at all.
Why does my flat roof only leak in heavy rain?
A flat roof that leaks only in hard rain can have an opening that sits above the normal water line, like the top edge of the wall flashing, a scupper or a seam near a drain. When drains back up or rain blows sideways, water rises high enough to reach it. A roofer can check those spots and the drains to find the one that's letting water in.
Can I just put sealant or roof cement on the leak?
Sealant can slow a small leak for a short time, but it doesn't fix the cause. On a TPO roof, roofing cement usually means that area can't be heat-welded later and has to be cut out. A lasting repair is a patch made from the same type of membrane, sealed the way the manufacturer calls for.
How fast can someone come out for a leak on my flat roof?
Call (737) 383-1768 and we'll set up the soonest inspection we can. If water is actively coming in, we can cover the area to protect the building until a full repair is done. Until then, move anything valuable away from the drip, catch the water, and take photos of the stain and any damage inside.
Does a flat roof repair in Austin have to be a white roof?
Not for most repairs. Under Austin's energy code, repairs that are smaller than half the roof or 2,000 square feet, whichever is less, don't have to meet the cool-roof requirement. Larger work on a low-slope roof over cooled space does. Roofs over spaces that aren't cooled are exempt. We'll check which rule applies to your roof.
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