Moisture Meter Inspection 101 for Roofers

A moisture meter reading can approve or deny a $15k supplement. Carriers have stopped accepting "wet decking" as a vague claim. They want documented percentage readings from a calibrated meter. Most reps have never used one. A 30-minute training and a $90 tool close that gap.

Pin vs Pinless Meters

TypeCost RangeUse Case Pin (invasive)$30-$120Direct contact reading in wood, drywall, plaster Pinless (non-invasive)$70-$400Surface scan, preserves material, faster Dual-mode$150-$450Both in one unit, versatile

For attic decking inspection, a dual-mode meter is the right pick. You scan pinless across the deck to find hot spots, then drive pins for an exact reading at those spots.

Recommended models:

• Flir MR176 (dual-mode, $350): professional-grade
• General Tools MMD7NP (dual-mode, $160): solid mid-range
• Klein Tools ET140 (pinless, $90): entry level
• Calculated Industries AccuMASTER Duo Pro (dual-mode, $130): budget dual

Reading Thresholds

Moisture content in wood decking:

ReadingConditionCarrier Response Under 12%Dry, normalNo claim 12-15%Elevated but borderlineOften denied 15-18%High, likely prior exposureCase-by-case 18-25%Active moisture concernSupplement valid 25%+Rot-active, saturatedFull replacement typical

18% is the generally accepted threshold where structural concern kicks in. Below that, carriers argue "surface moisture from humidity." Above that, fungal growth and rot become structurally significant.

The Inspection Routine

Step 1: Attic Access

Before climbing, check for:

• Visible daylight through the deck (indicates holes or gaps)
• Rodent activity or nesting
• Soot or smoke staining (past fire, changes scope)
• Standing water or obvious wet areas

Step 2: Meter Calibration

Test the meter on a known-dry piece of lumber (usually a 2x4 in the yard, reading 7-9%). If off by more than 2 points, replace the battery or calibrate per manual.

Step 3: Scan

Pinless scan across the deck from one corner to the other, moving in 12" grid rows. Note any spots above 12% with chalk.

Step 4: Pin Readings

At each chalked spot, drive pins and record the exact percentage. Photo the meter display with scale reference.

Step 5: Map It

Sketch a simple deck diagram. Mark each reading with its percentage and location. A rough drawing on a clipboard is fine, digital is better. RoofKnockers has a deck map tool built into the inspection record. See the inspection features.

Documenting for the Carrier

Your supplement package should include:

1. Photo of each meter reading with the display visible and a scale object
2. Deck map with readings overlaid
3. Photo of the wet area showing discoloration, staining, or fungal growth
4. Model and serial number of the meter used
5. Last calibration date (write on meter or in notes)
6. Weather data for the prior 30 days from NOAA if arguing recent storm moisture

Adjusters reject supplements that show a single reading without context. A reading map with 6-8 points tells a story: water entered here, traveled along the rafter, wicked into the decking over 18".

The Follow-Up Leak Test

After you have moisture readings, verify entry path with a leak test. Not always required but strengthens the supplement:

1. Identify suspected entry points: cracked flashing, nail pops, damaged shingles, valley breaks
2. Have a second person in the attic with the meter
3. Run a garden hose on the suspect area for 15 minutes (start low on the roof, work up)
4. Observer calls out any new readings or visible moisture
5. Document the entry path and the affected area

This is the test that wins contested supplements. A simple "here is the path" beats "here is a wet spot."

Common Mistakes

• Reading a wet rafter and claiming it is the deck. Be specific.
• Reading one spot and generalizing. Map the deck.
• Using a meter calibrated for drywall on wood. Different scales.
• Ignoring 16-17% readings on borderline claims. Document them with photos. Carriers sometimes approve at 17% with good leak path evidence.
• Running the leak test right before the adjuster arrives. Now everything is wet and you cannot prove which water is yours.

Meter Care

• Store with pins covered or retracted
• Keep a spare 9V battery in the truck
• Calibrate monthly with a known-dry reference
• Replace pins every 100 readings (pins bend and give false lows)

A $90 meter that lasts 2 years and closes even 3-4 supplements at $2,000 each is a 150x ROI.

Related: hail damage photo documentation, adjuster scope dispute playbook, and drone use for roof inspection.

See pricing or start a trial.

FAQ

Will the adjuster's own meter agree with mine?

Usually within 2 percentage points. If you read 22% and they read 14%, check calibration on both. Sometimes the adjuster's meter is old or miscalibrated. Be professional when comparing.

Is training required to use one?

No certification, but read the manual. The most common error is confusing the scale setting (wood vs drywall vs concrete). Wrong scale gives wrong numbers.

What about pinless through insulation?

Pinless meters read through some insulation (fiberglass) but not all (foam board blocks the signal). Remove insulation to get pin contact on the deck when possible.