How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

What causes moisture meters to have false readings?

Monday, November 16, 2020

There are three types of moisture evaluation devices and each uses a different technology. Pin-type meters measure electrical condutivity. Contactless meters check density with radio waves, and infrared cameras show differences in temperature across the surface of the material. Each type has its own unique advantages and shortcomings.


    Electrical conductivity increases in tandem with the moisture level in a material. But any salts that have settled in the material, such as from urine or other chemicals, also increase conductivity. Plus, these meters are primarily designed for measuring moisture in wood. The moisture readings are stated as a percentage of water in wood (% H20 WME - Percent Wood Moisture Equivalent). But a reading of 12% moisture in wood is dry, whereas 12% in brick is saturated. 

    So, when working with materials other than wood, it is often better to use a comparison of readings between a known dry area and one that is suspected of being wet, rather than relying solely on a single percentage reading, even with an adjusted range based on the material tested. And checking your conclusion with one or both of the other moisture meter types is always a good idea.

    Another limitation of pin-type meters is the damage caused by pin-penetration of a surface to get  a good reading. It is not necessary, or recommended, to push the pins all the way into a material. But, in most cases, you have to slightly puncture the surface to get a reading, and that may not be acceptable for some home owners. Also, some surfaces are too hard to be penetrated.


    These are good for a quick scan of an area within arm’s reach, and easily reset for different types of construction materials. But the readings jump up when over any hidden metals in the tested material, such as conduit, wiring, steel connectors, or foil backing on insulation. Again, cross-checking with another type meter is good due diligence.


    Best tool for a quick scan of a large area, although not as useful outdoors in daylight due to sun-induced temperture variations over surfaces. Because any moisture exposed to air will immediately begin to evaporate, and the evaporation cools the surface of the material, thermography uses this temperature difference to locate wet areas. But lower surface temperature in a location can also be caused by, for example, lack of insulation or a leaking air conditioning duct behind the material. An experienced thermographer can often tell the difference by the shape/pattern of the cool areas, although it is still possible to be fooled. So double-checking with another meter is good for verification.

    Calibration can also be an issue for any moisture meter, although being out-of-calibration is more likely for older contactless and infrared, rather than pin-type, meters.

    And then there is one final, low-tech tool. Your fingers are quite sensitive to wetness. “Fingertips are a great moisture-sensing tool. And the best part is that you recalibrate them every time you wash your hands,” according to Joe Lstiburek, a nationally known engineer and construction material researcher for Building Science Corporation. So, if an area looks suspicious, touch it to feel for wetness. Like the other types of moisture meters, fingers have their own limitation: moisture that does not reach the surface cannot be detected this way. 

    Also see our blog post What tools do you use for a home inspection? 

• • • • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of our blog posts about WATER INTRUSION:

How does a home inspector find roof leaks? What about wet spots in the walls?

Why does my concrete floor slab sweat and get slippery?

Do stains on the ceiling mean the roof is leaking? 

What causes sweating (condensation) on the inside of windows in the winter? 

Why does condensation form on the outside of some windows and not others in the morning?

How can I prevent mold in my Florida winter home when I'm gone for the summer? 

• My bathroom is stinky and humid even though it has an exhaust fan. What can I do to fix it?

Should I buy a house that has hurricane flood damage?  

Why do new homes have more moisture and mold problems than older houses?

What is the right humidity level in a mobile home? 

How do you test a shower pan for leaks?

Should I call a plumber or septic tank contractor when my septic tank backs up into the house? 

Why is old galvanized steel water pipe a problem for homebuyers?

What does polybutylene pipe look like? Why is it a problem?

What can I do to prevent roof leaks? 

The inspector says that a missing kickout flashing caused water damage inside the wall. What's "kickout flashing"? 

• Why is my roof leaking?

   Visit our WATER INTRUSION page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

Water Heaters

Water Heater Age

"What Are The

Signs Of..."

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests



When It First

Became Code

"Should I Buy A..."

Park Model Homes


Shingle Roofs




Wind Mitigation

Roof and Attic

"Does A Home


Pool and Spa

"What Is The Difference Between..."




Concrete and

Concrete Block

Metal Roofs


Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants


Older and

Historic Houses

Crawl Spaces

Mobile-Manufactured Homes

Building Permits

Life Expectancy

Clay Soil





Exterior Walls

& Structures


Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers



Doors and Windows



Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps


Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.






Air Conditioner & Furnace Age/Size


Electrical Switches





Water Intrusion

Electrical - Old

and Obsolete


Foundation Certifications

Tiny Houses

About McGarry and Madsen



Buying a home in North/Central Florida? Check our price for a  team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.

Moisture Problems

Crawl Spaces