How leaks travel on a low slope roof
Water enters at a small breach, soaks into the insulation, follows the path of least resistance (insulation joints, deck flutes, low spots) and shows up inside the building somewhere downstream. The visible water stain is the symptom. The breach is somewhere uphill.
On metal deck, water often runs along a single deck flute for many feet before dropping through a fastener hole. On wood deck, it spreads across joists. Either way, the interior drip is rarely directly below the roof problem.
The right way to find a leak
1. Start indoors
Photograph the interior staining. Note the exact location relative to columns or fixed reference points. Check if the stain has moved or grown.
2. Translate to the roof
Mark the corresponding spot on the roof using the same reference points. This is where you start, not where you'll find the breach.
3. Walk uphill
Look at every seam, every penetration, and every transition uphill of the interior leak. Probe suspect areas. Note ponding zones.
4. Check the obvious suspects
- Pipe boots and HVAC curbs.
- Drain bowls and overflow scuppers.
- Parapet flashings and counterflashing.
- Skylight curbs.
- Recent rooftop work (antenna, equipment installs).
5. Consider moisture survey
If walking the roof doesn't pinpoint the breach, infrared imaging or core sampling can show how far moisture has spread inside the insulation. That often points back to the original entry point.
Why patches fail
- Repair done over wet insulation. The water has nowhere to go and the patch eventually fails from below.
- Wrong material. Roofing tar over EPDM, or cold-applied sealant where a heat weld was needed.
- Insufficient overlap or surface prep.
- Patching only the visible damage and missing the actual breach location.
- Skipping flashing repair because the membrane "looks fine."
A proper repair
- Locate the actual breach, not just the visible interior leak.
- Open the membrane if needed to check insulation. Replace any saturated insulation board.
- Allow deck to dry, or accelerate with controlled heat.
- Install a compatible repair patch using manufacturer-approved details (heat weld on TPO, EPDM patch with primer and seam tape, etc.).
- Verify with a water test on the most suspect area before leaving.
- Document with photos and a written repair report.
When to call for emergency service
- Active water entry into occupied space.
- Water near electrical panels or sensitive equipment.
- Multiple new leaks after the same storm event.
- Storm damage with visible roof debris or membrane lifting.
For Northern Indiana commercial property owners, we keep emergency leak response staffing available. Calls usually get same-day or next-business-day on-site response during weekday hours, weather permitting.
Temporary measures while you wait
- Move inventory and equipment out from under active drips.
- Bucket and tarp inside, not on the roof.
- Photograph the interior damage for insurance.
- Do not climb on a wet flat roof yourself.
- Do not apply roofing tar or asphalt patch. Both can compromise the proper repair and void warranties.
Indiana-specific leak patterns
Most of the leak calls we get across South Bend, Mishawaka, and Elkhart spike during two windows: spring snowmelt with rain on top, and August thunderstorms with wind-driven rain. Both stress flashings and seams in ways quiet rain doesn't. Worth planning your inspection schedule around those windows.