The Short Answer
Roofers find leaks by working backward from the stain: inspecting the attic for water trails, inspecting the roof at flashings, penetrations and valleys above that area, and taking moisture readings. When the source is not obvious, they water-test sections of the roof one at a time, starting low, until the leak reappears. Flat roofs may also get infrared, electronic or core-cut surveys. A good diagnosis ends with photos of the entry point and the reason it failed.
Key Points
- The attic usually tells more than the ceiling, because it shows the water's path.
- Controlled water testing is slow but it confirms the source instead of guessing.
- Infrared and electronic leak detection are mainly flat-roof tools with real limits.
- One stain can have more than one entry point, so a good roofer keeps looking after the first find.
Why Leaks Are Hard to Find
Water that gets past a shingle or flashing rarely drops straight down. It runs along the top of the underlayment or the deck, follows a rafter or a truss, rides along ductwork or a vapor barrier, and lets go wherever gravity finally wins. The ceiling stain can be several feet, or a full room, away from the entry point.
Leaks are also inconsistent. Some appear only with wind-driven rain from one direction. Others show up only during an ice dam or a fast thaw, when water is pushed uphill under shingles. Condensation in the attic can look exactly like a leak. A diagnosis has to account for all of that, which is why a quick look from the driveway is not enough.
Why roof leaks show up far from the source
How water travels along decking, rafters and ductwork, and how to trace it from the attic.
Read the guideThe Tools Roofers Use, and What Each Can and Cannot Do
Attic inspection
Usually the first step
Following stains, water trails, dark or soft wood and wet insulation uphill from the ceiling stain toward the entry point. It also reveals condensation, frost and bath fans venting into the attic. It misses leaks that run inside the wall or above a finished ceiling with no attic access.
Roof surface inspection
Every flashing and penetration
A close look at the roof above the suspect area: flashings at walls and chimneys, pipe boots, vents, skylights, valleys, nail heads and lifted or creased shingles. It finds most obvious failures but cannot see what is under an intact-looking shingle or behind sealant.
Moisture meter readings
Wood and roof assemblies
Handheld meters show whether decking, framing or insulation is wet now, which helps map how far water has spread. Readings show that something is wet, not why, and they are affected by temperature and material type.
Controlled water testing
Confirms the source
Running water on one section of roof at a time, starting at the lowest suspect point and moving up, while someone watches inside. It reproduces rain leaks well. It cannot easily reproduce ice dams or wind-driven rain, and it takes time.
Infrared thermography
Mainly low-slope roofs
A thermal camera shows areas of wet insulation that hold heat differently from dry areas. It needs the right conditions and is generally limited to adhered, unballasted membranes, and readings must be confirmed by other methods.
Electronic leak detection
Membrane roofs
Specialized equipment finds breaches in waterproof membranes by measuring electrical conductance. ASTM's guide for the method says it is meant to be used alongside visual, infrared and other inspection, not to replace them.
Core cuts
Flat roofs
A small sample cut through a flat roof to see the layers and confirm whether insulation is wet. It is destructive, so it is patched immediately, and it shows only that one spot.
What a Careful Leak Diagnosis Looks Like
- Step 1
Start With Your History
When does it leak, in what weather, from which direction, for how long? A leak that only appears in February points somewhere very different from one that appears in every summer storm.
- Step 2
Map the Inside
Locate the stain, then go into the attic and follow the trail uphill, measuring from a fixed point such as an exterior wall or a vent pipe so the location can be found from the roof.
- Step 3
Inspect the Roof Above
Check every detail upslope of the trail: flashings, boots, vents, valleys, skylights and nails. The code requires flashing at wall and roof intersections, changes of slope and roof openings, and those are where most leaks start.
- Step 4
Measure Moisture
Use a meter on decking, framing or insulation to see how far the water has spread and whether rot is likely.
- Step 5
Test When It Is Not Obvious
Isolate and water-test one area at a time, low to high, until the leak shows. Then keep going, because one stain can be fed by two or three entry points.
- Step 6
Document the Cause
Photograph the entry point, the reason it failed, and any damage to the deck, so the repair can be scoped and later checked.
Instrument Surveys on Flat and Low-Slope Roofs
On commercial and residential flat roofs, water can travel a long way inside insulation before it shows, and a stain may be far from the breach. That is where instrument surveys earn their cost. Infrared works because wet insulation holds heat longer than dry insulation, but published industry guidance lists real conditions: no significant rain for about 48 hours, wind under about 15 mph, air above about 50 degrees, a dry surface, and sun or a strong indoor to outdoor temperature difference. Heavy ballast or pavers can prevent a useful scan. In West Michigan that narrows the windows considerably.
Electronic leak detection, covered by ASTM D7877, finds breaches in electrically insulating membranes and is used alongside visual and other inspections. Core cuts confirm what the instruments suggest. A good flat-roof diagnosis combines methods rather than relying on one.
Flat roof repair
How we find and fix leaks on membrane, modified bitumen and other flat roofs.
Flat roof repairTracing Ice Dam Leaks Against Michigan's Ice Barrier Rule
In West Michigan a large share of winter leaks are not holes at all. NOAA's 1991 to 2020 normals put Grand Rapids snowfall at about 78 inches a season, with about 61 inches of it falling from December through February. When snow on a warm roof melts and refreezes at the cold eave, the ice holds back meltwater, which can work up under shingles that shed water perfectly well in rain. A hose test in July will not reproduce that, which is why the season and the location of the stain matter so much in a winter diagnosis.
The 2015 Michigan Residential Code gives the diagnosis a reference line. Section R905.1.2 requires an ice barrier where the local climate table shows a history of ice forming along the eaves: either two layers of underlayment cemented together or a self-adhering polymer modified bitumen sheet, running from the lowest edge of the roof to a point at least 24 inches inside the exterior wall line. On roofs of 8 in 12 or steeper, it must also extend at least 36 inches measured along the slope from the eave. Detached accessory structures without conditioned floor area are exempt.
That line tells a roofer where to look. A stain that appears on a thaw day just inside an exterior wall suggests water backed up at the eave. If the roof has an ice barrier, the question becomes whether the backup reached beyond it or found a gap such as an unsealed seam, a nail through the membrane or flashing that was not lapped into it. If the roof predates the rule or was re-covered without one, that is a finding to put in the report. A careful roofer confirms which it is by checking the eave, not by assuming. The cause of the ice itself, heat escaping into the attic, is usually an insulation and air sealing problem for another trade.
Michigan's ice barrier requirement
Where the code requires it, how far it must reach and what it means on an eave repair.
Read the guideWhat a Good Leak Diagnosis Should Give You
Whether the diagnosis comes with a free inspection or a paid service call, you should leave with enough information to understand the problem and compare quotes. Ask for these, in writing or by email.
- Where the water enters, marked on a photo or a simple sketch
- Why it failed: worn boot, missing kickout, reused step flashing, ice dam, condensation
- How it was confirmed: visual, attic trail, moisture readings or water test
- How far the damage extends, including deck or framing condition
- Any other entry points found or suspected
- The recommended repair, and an alternative if there is one, with prices
- Whether the cause is the roof at all, or another trade such as siding, masonry or ventilation
Signs a Diagnosis Is a Guess
- A price over the phone for a leak nobody has looked at
- No trip into the attic when there is an accessible one
- A recommendation for a full replacement with no photos of failure across the roof
- A sealant-only fix with no explanation of what failed
- No mention of condensation when the leak appears only on cold days
How Stellar Traces a Leak
We inspect the roof surface, every flashing and every penetration, and the attic. We use moisture readings and, when the source is not obvious, controlled water testing, isolating sections of the roof one at a time until the leak shows. Then we look for a second source, because one stain is often fed by more than one entry point.
Inspections are free. If the leak turns out not to be the roof, such as water behind siding or attic condensation, we tell you which trade to call. Every repair starts at $500, and most carry a 10 to 15 year craftsmanship warranty.
Leak-Finding Methods Compared
| Method | Best at | Misses or limits |
|---|---|---|
| Attic inspection | Showing the water's path and condensation | Leaks inside walls or finished ceilings |
| Roof surface inspection | Visible failures at flashings and penetrations | Problems under intact-looking shingles |
| Moisture meter | How far water has spread | Why it got there |
| Water test | Confirming a rain leak's source | Ice dams, wind-driven rain; slow |
| Infrared | Wet insulation on flat roofs | Needs specific weather; ballasted roofs |
| Electronic leak detection | Membrane breaches | Used with other methods, not alone |
| Core cut | Confirming wet layers | One spot only; must be patched |
Need the Leak Found, Not Guessed?
Our inspection covers the roof and the attic, and we confirm the source before we price the repair. Free, with photos.
Related Guides
Attic Condensation or Roof Leak?
Frost on nails, attic rain on thaw days, and how to tell it from a leak.
Learn MoreRoof Leaks Only in Heavy Rain or Wind
Why some leaks only show in certain storms, and how to log them.
Learn MoreHow to Describe a Roof Leak When You Call
The details that make a diagnosis faster.
Learn MoreRoof Leak Repair
How we trace and fix leaks across West Michigan.
Learn MoreQuestions We Hear
How long does it take to find a roof leak?
An obvious leak, such as a cracked pipe boot with a matching trail in the attic, can be confirmed in under an hour. An intermittent leak that needs water testing can take several hours, because each section of roof is tested separately and given time to show. Some leaks that only appear with ice dams or a certain wind direction cannot be reproduced on demand and are confirmed by elimination.
Can a leak be found when it is not raining?
Often, yes. Stains, water trails, dark or soft wood and moisture readings remain after the rain stops, and a visible failure on the roof usually lines up with them. When the evidence is unclear, a controlled water test recreates the rain on one section at a time. Leaks caused by ice dams are the exception and may only be confirmed in winter.
Do roofers use thermal cameras on houses?
Some do, but infrared is mainly a flat-roof tool. On a sloped shingle roof with a vented attic, temperature differences come from many things besides water, and the published conditions for a reliable scan are narrow. On a house, the attic, the roof surface and moisture readings usually tell more. Ask what an infrared scan would add before paying extra for one.
What if the roofer cannot find the leak?
It happens with intermittent leaks. A good roofer will tell you what was ruled out, what is still suspected and how to catch the leak next time, such as checking the attic during the specific weather that causes it. Keep a log of dates, weather and wind direction. Be cautious of anyone who replaces large areas without having confirmed a source.
What This Page Cites
- ASTM D7877, Standard Guide for Electronic Methods for Detecting and Locating Leaks in Waterproof Membranes, ASTM International (https://www.astm.org/d7877-14.html), accessed October 2026
- Lucier, R., Daytime Infrared Roof Inspections, IIBEC Interface, August 2004, International Institute of Building Enclosure Consultants (https://iibec.org/publication-post/2004-08-lucier/), accessed October 2026
- 2015 Michigan Residential Code, Section R905.1.2 Ice barriers, UpCodes (https://up.codes/viewer/michigan/mi-residential-code-2015/chapter/9/roof-assemblies), accessed October 2026
- U.S. Climate Normals 1991 to 2020, monthly snowfall normals for Grand Rapids Gerald R. Ford International Airport (USW00094860), NOAA National Centers for Environmental Information (https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-monthly-1991-2020&stations=USW00094860), accessed October 2026
- 2015 Michigan Residential Code, Chapter 9 Roof Assemblies (R903.2 Flashing, R903.2.1 Locations), International Code Council (https://codes.iccsafe.org/content/MIRC2015P2/chapter-9-roof-assemblies), accessed October 2026