Imagine finally getting into your dentist’s office to have that tooth that’s been bothering you fixed.
But just as they're about to get to work, the dentist clearly holds your x-ray upside down. And that tray of drills and bits right next to you? You can hear the dentist quietly asking the assistant what each one is and how it works.
How comfortable are you with your dentist?
When it comes to testing for moisture, a home inspector isn’t dissimilar from a dentist. A home inspector should be able to complete the job and leave the client with results they’re happy with.
And like a dentist about to restore a tooth, a home inspector’s ability to do their job effectively is rooted in having the necessary equipment and a proficiency in understanding readings.
Taking and interpreting moisture measurements accurately starts with understanding how a moisture meter works.
There are two types of meters used in moisture surveys: pinless and pin-type meters.
Non-invasive, a pinless moisture meter does not break the surface of the material being tested. Using conductance it detects dampness by assessing the average moisture of a material within its depth of measurement. Non-penetrating moisture meters don’t tell you actual moisture content -- they help confirm the presence of moisture within a substance. Pinless moisture meters allow for quick initial inspections to locate the source of a moisture issue, even if it’s beneath flooring or behind wall coverings.
Made to measure actual moisture content, pin-type meters detect moisture through direct contact with the material being tested. Pin-type meters use electrodes, which barely break a material’s surface, to measure the electrical resistance between its probes. With readings representative of actual moisture content in wood and WME (see below) in a wide range of building materials, pin-type meter measurements should be used to confirm the readings found by a pinless meter and are the predominant confirmation of excessive moisture.
During home moisture inspections, there are myriad materials to test, such as:
Unless you’re using a material-specific meter, your pin-type moisture meter is calibrated to measure wood moisture equivalent (WME).
Wood is the barometer for measuring moisture in other materials. Why wood? It has a similar level of electrical conductivity across species and absorbs or releases moisture depending on environmental conditions.
Understanding a pin-type meter’s readings is straightforward -- the meter gives you a quantitative measurement of a material’s moisture content as if it were wood. The higher the percent value, the more moisture has saturated a material.
As non-invasive meters are testing for moisture presence -- the extent of which can later be confirmed by pin-type meter readings -- pinless moisture meters give you a qualitative reading. In other words, they tell you whether a material is wet or dry.
That’s where a moisture meter reference scale -- such as the one to the right from the USDA -- comes into play. All materials have different thresholds for what’s considered damp or dry -- an acceptable moisture content by weight in wood is not the same for concrete. Taking measurements using a reference scale lets you determine moisture’s presence, regardless of material type. You’ll also get a general idea of how much moisture a material has in it.
Most reference scale readings are displayed numerically with a color-coded scale. Readings in green mean there’s a low moisture presence, while those in red indicate a concerning level.
When evaluating moisture presence with a reference scale, it’s critical to establish a baseline reading by measuring a dry sample of the material being tested. From there, additional readings are comparable to what’s known as dry, making it easier to assess the extent of moisture presence.
It’s important to note the reference scale does not represent actual moisture content levels; the readings are a relative measure of moisture presence. For instance, a reading of 30% does not mean a material contains 30% moisture content. The reading indicates that wood in close proximity or in contact with that material will equilibrate at 30% and therefore support microbial growth.
Moisture measurements are only as good as the tool taking them.
Regardless of if you’re using a pinless vs. pin moisture meter, here are a few tips to make sure your meter is performing as it should:
A cheap moisture meter is just that -- cheap. Most inexpensive meters aren’t meant to last long. They’re not durable. And they usually have limited functionality. Spending the extra money on a more expensive meter is an investment in reliability. Expensive meters are designed for the demands of the job and have a long useful life.
That time you accidentally dropped your moisture meter from 10 ft. up a ladder can affect its performance later on. Bent electrodes, dented contact plates, or broken internal components all impact a meter’s ability to take measurements accurately. A quick once-over of your moisture meter to make sure it’s in good working order saves you from redoing an inspection for an unhappy customer.
A few test runs for moisture measurements before an inspection goes a long way, too, in saving time and headache. Most meters have a calibration function or come with a testing device to verify accuracy long before you start work.
Taking moisture readings you can be confident doesn’t happen by measuring once. By taking several readings in the same spot, you’ll have a better gauge of the amount of moisture in a material. If a reading seems off, taking a few more in and around the immediate area can confirm your suspicions of a malfunctioning meter. Consider it a survey of your survey to verify results.
During a home inspection if you find moisture use both pin and pinless functions to try and find the source of moisture. Home inspectors should use their own experience and understand what the meters are telling them if they are making an assumption for the cause of the moisture problem.
Accurately and effectively surveying for moisture is not only about knowing how to use a moisture meter, but also understanding what its measurements are telling you.