Quick answer
A roof moisture inspection is a survey that finds water trapped inside a roof, usually in the insulation under a flat or low-slope membrane, using infrared cameras, electrical impedance scanners or nuclear gauges, then confirms the readings with small core cuts.
It answers a question a normal inspection cannot: how much of the roof is wet under a surface that looks fine. That decides between spot repair, a recover and a full tear-off.
Quick facts
Key takeaways
- A roof moisture inspection finds water hidden inside a roof, mainly in the insulation under a flat or low-slope membrane.
- The three main tools are infrared cameras, electrical impedance scanners and nuclear gauges.
- All three give relative readings. Core cuts, weighed wet and dry, confirm what is really wet.
- A survey shows where the roof is wet, not why. Finding the leak path is a separate job.
- Code does not allow a new roof over a water-soaked one, so a survey can decide between recover and tear-off.
What a roof moisture inspection is
Water that gets into a roof does not always drip into the room below.
On a flat or low-slope roof, it often soaks into the insulation boards under the membrane and stays there. The surface looks fine.
The insulation slowly loses its value, the deck under it can rust or rot, and the wet area grows.
A moisture inspection, also called a moisture survey, maps those wet areas without tearing the roof apart. The inspector scans the whole roof with an instrument, marks the spots that read differently, and then cuts a few small samples to check. The result is a roof plan with the wet areas drawn on it.
This is different from a normal roof inspection, which looks at the surface, flashing and attic. It is also different from finding a single leak. A survey tells you how much of the roof is wet; it does not say where the water came in.
How moisture shows up to the instruments
Wet materials behave differently from dry ones. They hold heat longer, they conduct electricity better, and they contain more hydrogen, because water is hydrogen and oxygen. Each survey method reads one of those differences.
Professional Roofing, the magazine of the National Roofing Contractors Association, explains the heat effect simply: during the day the sun warms the roof, and at night the wet areas hold that heat longer than the dry areas 3.
An infrared camera sees the warmer patches. The same article stresses that infrared tools do not see moisture. They see temperature differences, which can also come from other causes 3.
Nuclear and capacitance meters take single readings at points on a grid laid out across the roof, typically 5 to 10 feet apart 3. Points that read high are marked, and a map of wet zones is drawn from the pattern.
Types of moisture survey
Each method has a standard or a clear way of working, and each has roofs it suits and roofs it does not.
| Method | What it reads | How it is done | Watch out for |
|---|---|---|---|
| Infrared thermography | Heat held by wet insulation | Camera scan at night after a sunny day, from the roof or the air; ASTM C1153 1 | Sees temperature, not water; weather and roof build change results |
| Electrical impedance (capacitance) | How well the roof layers conduct a small signal | Scanner rolled over the roof, or point readings on a grid; ASTM D7954 2 | Not suited to metal surfaces, black EPDM, or foil-faced insulation 2 |
| Nuclear gauge | Hydrogen in the layers below the meter | Point readings on a grid; fast neutrons are slowed by hydrogen in water 3 | Uses a small radioactive source, so it is specialist equipment |
| Core cuts | Actual water content of a sample | Small plugs cut out, weighed wet, dried and weighed again 3 | Destructive, so few are taken; each hole must be repaired |
| Pin meters | Electrical resistance between two pins | Pushed into exposed material | Relative readings that need checking against weighed samples 3 |
Infrared roof inspection and ASTM C1153
ASTM C1153 is the standard practice for finding wet insulation in roofs with infrared imaging. Its scope says it applies to infrared imaging done at night, on roofs where the insulation sits above the deck and in contact with the waterproofing. It covers both ground-based and aerial work 1.
The standard sets minimum conditions for the equipment and the weather, because both change what the camera sees. It also covers checking the infrared results with invasive tests, such as cores. And it says plainly that it does not give methods to find the cause of the moisture or its point of entry 1.
Night work on a roof is risky, which is why aerial and drone infrared have grown. A drone can scan a large flat roof quickly with a thermal camera. The rules for the pilot are covered below.
A warm patch is not a wet patch yet
An infrared image shows temperature differences, not water 3. A warm area marks a place to test. Only a core or a second method confirms moisture.
Capacitance and impedance scanning, ASTM D7954
ASTM D7954/D7954M covers moisture surveys with nondestructive electrical impedance scanners. Its scope is insulated low-slope roofs and waterproofing where the insulation sits above the deck under a membrane that does not conduct electricity, such as asphalt, coal tar, modified bitumen, thermoplastics or spray foam.
It also covers some systems with no insulation over a deck that can absorb water 2.
The scanner sends a small signal into the roof. Wet layers let more of it through. The standard lists roofs where this does not work well: metal surfaces, black EPDM, foil-faced insulation and some membrane combinations, because they conduct or give false high readings 2.
Impedance surveys can be done by day, which makes them easier to schedule than night infrared. Like every method here, they give comparative readings, not a measured water content.
Worked example: from scan to core
An illustrative survey on a warehouse roof, showing how the steps fit together.
| Step | What happens | Result |
|---|---|---|
| Grid | Points marked 10 feet apart across the roof | A map with one reading per point |
| Scan | Impedance readings at each point | A cluster of high readings near one drain |
| Core: dry area | Sample cut where readings were low | Baseline weight for dry insulation |
| Core: wet area | Sample cut in the high cluster | Weighed, dried, weighed again |
| Moisture content | (wet weight minus dry weight) divided by dry weight, times 100 3 | Confirms the cluster is wet, not a false reading |
| Report | Roof plan with wet zones drawn and sized | Basis for repair or replacement scope |
MC (%) = (wet weight − dry weight) ÷ dry weight × 100
MC- Moisture content of the sample, as a percent of its dry weight
Wet weight- The core as cut from the roof
Dry weight- The same core after it is oven-dried
The scan finds suspect areas; this core math is what confirms them 3.
Source: [3]
Illustrative steps only; the grid spacing and number of cores are the surveyor's choice for each roof. The formula is the one Professional Roofing gives for gravimetric analysis.
Where moisture surveys are used
Moisture surveys are mostly used on low-slope and flat roofs, which is where the methods and standards are aimed. Commercial buildings, schools, warehouses and apartment blocks use them most.
On a house with a sloped shingle roof, the insulation usually sits in the attic, not on top of the deck, so there is little for these tools to find.
On homes, the closest use is infrared from inside the house or attic, to spot damp ceilings and wet insulation after a leak. That can help, but it is not the roof survey these standards describe.
Drone inspections and the FAA Part 107 rules
A drone roof inspection uses a drone to take photos, video or thermal images of a roof. It keeps people off steep or fragile roofs and can cover a big flat roof fast. In the US, flying for business falls under the FAA's small drone rules, 14 CFR Part 107.
Under section 107.12, no one may fly a small drone unless they hold a remote pilot certificate with a small drone rating, or they fly under the direct supervision of a certified remote pilot who can take control at once 4.
Pilots must also keep their knowledge current within the previous 24 calendar months 5.
Two flight rules matter on roof work. The drone must stay within sight of the pilot, with no aid other than glasses 6.
And it may not fly higher than 400 feet above the ground, unless it stays within 400 feet of a structure and no more than 400 feet above its top 7.
Ask any drone inspector for their remote pilot certificate before they fly.
What a moisture survey is good for
Benefits
- Finds wet areas before they spread or rot the deck
- Lets you replace only the wet part, not the whole roof
- Shows whether a recover over the old roof is allowed
Who it helps
- Owners deciding between repair, recover and tear-off
- Buyers of commercial buildings who need a clear picture
- Roofers who want to price a scope based on facts, not guesses
What a moisture survey cannot do
- It does not find the leak. ASTM C1153 says it does not show the cause or the point of entry 1.
- Its readings are relative. Without cores, a high reading is a suspect, not proof 3.
- Some roofs are poor fits: metal, black EPDM and foil-faced insulation for impedance 2.
- Infrared depends on weather. A cloudy day or a wet surface can hide the pattern.
- It suits insulated flat roofs far more than sloped shingle roofs on houses.
What drives the cost of a moisture survey
This page does not give prices. The main cost drivers are roof size, the method, and access. Night infrared needs a trained team on the roof after dark or a drone with a thermal camera.
Grid surveys with impedance or nuclear meters take time per point, so a large roof with a tight grid takes longer. Each core cut adds labor and a repair to seal the hole.
The survey often saves money later. Knowing exactly how much of the roof is wet can shrink a full replacement to a section replacement, or show that a cheaper recover is not allowed. For sourced prices on repairs and replacement, see our cost guide.
How a survey is carried out
- The surveyor checks the roof build: membrane type, insulation type and deck, to pick a method that suits it.
- They check the weather. Infrared needs a clear, sunny day before a night scan; other methods need a dry surface.
- They lay out a grid or plan the scan path, and record readings across the whole roof.
- Suspect areas are marked on the roof and on a plan.
- Cores are cut in wet and dry areas, weighed, dried and weighed again.
- The holes are patched, and a report with the wet-area map goes to the owner.
Using surveys as part of roof upkeep
Some owners of large flat roofs have a survey done when a new roof is finished, to record a dry baseline, and then repeat it every few years or after a major storm.
Comparing maps shows whether wet areas are growing. ASTM D7954 names this use: surveys at completion, in preventive maintenance, and in condition assessments 2.
Between surveys, the basics still matter. Keep drains clear, fix splits and open seams quickly, and check flashing at walls and curbs. Most hidden moisture starts as a small opening that went unrepaired.
Risks and red flags
- No cores at all. A map built only on readings can mark dry areas as wet, or miss wet ones.
- A method that does not suit the roof, such as impedance on black EPDM.
- A survey used to sell a full replacement when the map shows only small wet areas.
- An uncertified drone pilot. Ask for the FAA remote pilot certificate.
- Walking a roof at night without proper fall protection. Surveys are work for trained crews, not owners.
Why the building code cares about wet roofs
The 2021 International Residential Code, section R908.3.1.1, says a new roof covering may not be installed over an existing one when the existing roof or covering is water soaked or has deteriorated 8.
So a moisture survey can decide whether a cheaper recover is even allowed, or whether the wet layers must come off first.
Code adoption, edition and local changes vary by jurisdiction. Ask your building department which edition applies.
Moisture inspection vs other roof checks
| Check | Question it answers | Main tools |
|---|---|---|
| Moisture inspection | How much of the roof is wet inside? | Infrared, impedance, nuclear, cores |
| Roof inspection | What condition is the roof surface, flashing and attic in? | Eyes, ladder, drone, attic visit |
| Leak detection | Where is water getting in? | Visual tracing, water testing, sometimes infrared |
| Damage assessment | What did a storm damage? | Close inspection, photos, test squares |
| Drone inspection | What does the surface look like from above? | Photo, video or thermal camera on a drone |
Common mix-ups
- Myth An infrared camera sees water.
- Reality It sees temperature differences. Wet insulation often shows as warmer at night, but other things can too.
- Myth A survey finds the leak.
- Reality It maps wet areas. The point of entry may be far from the wettest spot.
- Myth One method works on every roof.
- Reality Impedance does not suit metal or black EPDM, and infrared needs the right weather.
- Myth No cores means less damage, so it is better.
- Reality Without cores, the readings cannot be confirmed. A few small, patched holes are worth the certainty.
Local factors: climate, weather and rules
Climate changes how and when a survey can be done. Infrared needs a clear day to warm the roof and a dry surface at night, so humid or cloudy seasons shrink the working window.
Cold climates add condensation inside roofs, which a survey may pick up along with leaks. The building code edition your area uses decides whether a wet roof can be recovered.
Drone rules under Part 107 are federal, but some airports, parks and cities have airspace limits. We do not list local rules here; check with your building department and the FAA for your area.
When to get a moisture survey
- You own a flat or low-slope roof with insulation above the deck, and it has leaked.
- You are deciding between repair, recover and full replacement.
- You are buying a building and want to know how much of the roof is wet.
- A new roof was just finished and you want a dry baseline on file.
- Ask the surveyor which method suits your roof, how many cores they will take, and for their drone pilot certificate if they fly.
A standard roof inspection report may tell you a survey is needed. Our guide to choosing a roofer covers how to vet the contractor who does the follow-up work.
Keep going
- Roof inspectionThe standard surface and attic check
- ReroofingRecover vs tear-off rules
- Repair or replace calculatorWeigh the options once you know the wet area
- Drone roof inspectionShort definition in the glossary
Questions about roof moisture inspection
What is an infrared roof inspection?
It is a survey that uses a thermal camera, usually at night, to find warm patches on a roof where wet insulation is holding the day's heat.
ASTM C1153 is the standard practice for it. The camera sees temperature, not water, so the suspect areas are then checked with small core cuts before anyone relies on the map.
How accurate is a roof moisture survey?
It is good at finding areas that read differently, but every method gives relative readings. Professional Roofing says the results must be confirmed with core cuts and gravimetric analysis, which weighs samples wet and dry. A survey with well-placed cores is far more reliable than one with readings alone.
Can a moisture survey find where my roof is leaking?
Not on its own. It maps where the roof is wet, but water can travel inside a roof before it settles.
ASTM C1153 states that it does not give methods to find the cause or point of entry.
Leak tracing is a separate job, often done by checking flashing, seams and drains near the wet zone.
Do I need a moisture survey on a shingle roof?
Usually not. The standard methods are built for insulated low-slope roofs, where insulation sits above the deck under a membrane. On most sloped shingle roofs the insulation is in the attic, and an attic inspection shows wet deck or insulation directly. Infrared from inside can still help find damp ceilings.
Why is infrared done at night?
Because the sun warms the roof during the day and, after dark, wet areas cool more slowly than dry ones. That gap shows up on a thermal camera. ASTM C1153 applies to infrared imaging done at night, and it sets weather conditions for when the scan can be done.
What is a core cut on a roof?
A core cut is a small sample cut through the roof layers, down to the deck. It is weighed, dried and weighed again to find its real water content. Cores confirm whether a suspect area is wet. The holes are then patched, which is why surveyors take only as many as they need.
Does a drone pilot need a license to inspect my roof?
Yes, for business use in the US. Under FAA rule 14 CFR 107.12, the pilot needs a remote pilot certificate with a small drone rating, or must fly under the direct supervision of someone who has one. Pilots must also keep their knowledge current within 24 calendar months. Ask to see the certificate.
Which roofs are not suited to impedance scanning?
ASTM D7954 lists metal surfaces, black EPDM, foil-faced insulation and some membrane combinations as poor fits, because they conduct electricity or give false high readings. On those roofs, a surveyor may use infrared or a nuclear gauge instead, and still confirm the results with cores.
Can I put a new roof over a wet one?
No. The 2021 International Residential Code, section R908.3.1.1, does not allow a recover when the existing roof is water soaked or has deteriorated. Wet layers must come off first. A moisture survey shows how much of the roof that applies to, so the scope can be priced properly.
Sources
- ASTM International, C1153-23 Standard Practice for Location of Wet Insulation in Roofing Systems Using Infrared Imaging (abstract), retrieved .
- ASTM International, D7954/D7954M-22 Standard Practice for Moisture Surveying of Roofing and Waterproofing Systems Using Nondestructive Electrical Impedance Scanners (abstract), retrieved .
- Professional Roofing (NRCA), Michael T. Williams, "Surveying roof moisture" (Dec 2025/Jan 2026), retrieved .
- 14 CFR §107.12, Remote pilot certificate requirement (Cornell LII), retrieved .
- 14 CFR §107.65, Aeronautical knowledge recency (Cornell LII), retrieved .
- 14 CFR §107.31, Visual line of sight aircraft operation (Cornell LII), retrieved .
- 14 CFR §107.51, Operating limitations for small unmanned aircraft (Cornell LII), retrieved .
- International Code Council, 2021 International Residential Code §R908.3.1.1 Roof recover not permitted (Maryland adoption, read at UpCodes), retrieved .
Expert review
Written by the HyreRoof editorial team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Methods and limits checked against ASTM C1153 and D7954 abstracts and NRCA's Professional Roofing; drone rules read in 14 CFR Part 107; recover rule read in the 2021 IRC.
Suggest a correction. We fix errors and say what changed.