A Home Inspector’s Guide to Moisture Testing

Do you want to learn how to perform moisture testing for a home inspection?

Whether you’re a licensed home inspector or a concerned homeowner wondering whether your basement walls are a mold risk, we’ve got you covered.

We’ll show you the ins and outs of moisture testing with this straightforward guide. We’ll explain:

• Why you should test moisture content
• How to test for moisture
• Where you should measure
• General guidelines for using a moisture meter
• What your moisture meter readings mean
• How to keep track of those readings

Let’s get started!

Why you should test moisture content

It’s important to check for moisture content (MC) because too much moisture could cause extensive (and expensive!) damage to a home. Water intrusion can lead to mold growth, water stains, and distortions in the color and shape of floors, walls, cabinetry, and more.

Moisture testing helps you to identify high moisture areas and mitigate these problems.

It can also help determine what kind of action you need to take with oversaturated walls or floors. Your results can tell you whether you’ll need to bring in a dehumidifier or remove the entire material.

How to test for moisture

Though wood moisture meters are only designed to measure the MC of wooden materials, they can help you determine the difference between wet and dry non-wood materials.

No matter what you’re measuring, you’ve got two options. You can either use a pinless meter or a pin meter.

We’ve found that pinless moisture meters work better than pin-type moisture meters because they don’t require you to push in pins or drill into a material to measure it. This is a huge benefit for building inspectors and homeowners who don’t want to damage walls and floors to determine MC.

This also makes them a lot easier and faster to use than pin-type models.

Like any type of tool, there are some guidelines you’ll need to follow to get the most accurate results possible. We’ll cover those in an upcoming section.

Where you should measure

Though excessive moisture may exist in any area of the home, some areas are more susceptible to water infiltration than others. We recommend checking the following common problem areas:¹

• Bathroom: From the sink to the shower, this room has many opportunities for water damage. Leaky pipes and shower steam can cause a lot of excess moisture, leading to rotting subfloors and moldy walls.
• Basement: Basements are susceptible to flooding damage. Be sure to check the basement if it’s been raining a lot lately or if it seems musty and damp.
• Kitchen: The most frequent cause of moisture damage in kitchens is none other than the kitchen sink. Check the pipes for any signs of leaks.
• Laundry room: The washing machine is the greatest source of water damage in the laundry room. Look behind the washing machine for any leaks or wet spots.
• Attic: The roof of can leak and bring rainwater into the attic. Examine the attic ceiling for any holes, and the insulation for any dampness or mold.

Beyond these rooms, check any floors, subfloors, walls, or ceilings that show signs of water intrusion. This includes any furniture or cabinetry that seems damp or smells like mildew.

It’s also a good idea to check potential sources for water leaks like:

• Pipes
• Faucets
• Windows
• Some appliances (like dishwashers and laundry machines)

Let’s look at some best practices for using a moisture meter to do so.

General guidelines for using a moisture meter

There are certain procedures to keep in mind when you’re using a moisture meter for home inspection purposes.
Ensure that:

• Your meter is using the right setting: You won’t get accurate readings if you’re using the wrong calibration. Calibrate the meter for wood species, or use relative mode to measure other building materials.
• You avoid measuring over metal pieces: Placing a meter over a surface that has metal inside can distort the readings. Make sure there are no metal pieces underneath the surface you’re measuring.
• You measure on a smooth, flat surface: Pinless meters get the most accurate readings when you measure on a smooth, flat surface. Any rough spots in the surface you’re measuring or any surface moisture could throw off the readings.
• You take more than one reading: You’ll want to have many readings in the area you’re testing. For example, if you’re testing a wet spot on the wall, also test different portions of the wall around it.
• You take the appropriate safety measures: Wear safety equipment like a hard hat, safety goggles, insulated gloves, and respirators to protect yourself.

Once you’ve taken readings with a moisture meter, it’s time to understand what they mean.

What your moisture meter readings mean

Wood moisture meters measure the amount of water in a piece of wood. This means if your moisture meter says a piece of wood is 9%, then 9% of that wood’s weight is made up of moisture.

If this MC matches the equilibrium moisture content (EMC) of a given environment, you’ll know your wood doesn’t contain excess amounts of moisture. Typically, the MC of wood located inside your home should be within 6–9%. (Visit “How to Read a Moisture Meter” to learn more details of interpreting your meter’s readings.)

Though moisture meters are incredibly useful tools for moisture testing, they do have some limitations. And these will be important to know as you measure other kinds of material besides wood.

What a moisture meter can’t tell you

While wood moisture meters can give you exact numbers for solid wood, they can’t give you the exact MC of non-wood materials like concrete slabs, drywall, and carpets. They can only give a relative reading based off of a baseline.

This means it can show you which areas have higher levels of moisture than others.

Also, while moisture meters can reveal moisture problems, they can’t tell you for certain what the source of that moisture is or whether it will lead to mold later down the road.

When you’re writing your inspection report, make sure your clients know that your moisture meter can’t tell you where mold is, although it can reveal areas that may need further investigation.

How to keep track of moisture readings

Write down or record in some way any measurements you take. Include the date and location of the measurement, plus any notes that would be useful for the future.

A record enables you to point back to your results if you’re ever questioned about your moisture readings. You can also use your records to verify that you’ve followed standard procedures, increasing trust with your clients.

Equip yourself for effective moisture inspections

Whether you’re a home inspector or a homeowner inspecting your own house, you want to conduct moisture testing that follows industry standards and produces accurate readings.

We’ve already shown you where to look for moisture intrusion and helped you understand how to use moisture meters. Now, all you need is a quality tool to get started!

Take a look at “The Ultimate Guide to Buying the Best Moisture Meter for You” to learn what kind of moisture meter you’re going to need.