What Moisture Level Does Mold Grow At?

What causes mold growth?

Mold grows when mold spores enter a home and latch onto a moist surface.²

For an indoor environment, moist surfaces can be a result of leaks, humidity that exceeds 50%,³ or when the moisture content (MC) of a material exceeds normal moisture levels (like when wood materials have an MC greater than 20%⁴).

Mold feeds off organic materials, particularly cellulose building materials like paper, wood, fabric, and drywall.⁵ If the mold isn’t removed, it could continue to spread, causing it to become an even bigger hazard.

That’s why organic matter must be checked for high moisture levels that could lead to mold.

Where you should check for mold

Because mold grows in moist environments, some areas in the home are more susceptible to harboring excess moisture than others.

This concerns any area that allows for moisture intrusion, such as:

• Bathrooms
• Laundry rooms
• Kitchens
• Basements
• Attics
• Crawl spaces

You’ll especially want to check for mold around sources of moisture like:

• Sinks
• Showers or bathtubs
• Toilets
• Washing machines
• Clothes dryers
• Dishwashers
• Refrigerators
• Windows
• Air conditioners
• Humidifiers
• Air vents

Besides regularly monitoring these areas, you’ll want to keep an eye out for water leaks and humid weather that could lead to high indoor humidity levels.

You’ll know you’ve found moisture damage (and the potential for mold growth) when you spot certain signs.

More on that next.

Signs of potential mold growth

Several things indicate high moisture levels that could lead to mold problems.

These signs include:⁶

• A musty smell
• Warped walls
• Dark spots
• Creaking floorboards
• Discoloration
• Water stains
• Delamination
• Buckling
• Peeled or bubbled wallpaper

It’s crucial to keep an eye out for water damage and remove mold as soon as it appears to reduce its harmful effects.

The risks of mold growth

Mold poses a risk to your home and your health.

The very presence of mold indicates dangerously high moisture levels that may lead to rotting and structural damage.

Besides being a sign of excess moisture, mold can cause health problems for those with stressed immune systems or mold allergies.⁷ Especially with long-term exposure.

Some of the potential health effects of mold exposure include:⁸

• Coughing
• Sneezing
• Watery, itching, or burning eyes
• Itchy throat
• Stuffy nose
• Wheezing
• Dry skin
• Rash
• Allergic reactions
• Shortness of breath
• Headaches
• Fever

While you might be tempted to shrug off mold as a small issue that only results in unsightly walls and a few sniffles here and there, it’s important to remember the impact air quality has on our health.

You wouldn’t want to be breathing polluted air outside, so why would you want to be breathing contaminated indoor air, where, studies say, Americans spend 90% of their time?⁹

The effects of mold exposure are reason enough to remove mold as soon as possible.

So how should you get rid of indoor mold?

First, eliminate the source of moisture. If there’s a leak, fix it. If the humidity is too high, increase ventilation and bring in dehumidifiers.

Once you do that, you’ll want to clean.

Whether you’re dealing with wood or other building materials, experts recommend scrubbing moldy surfaces with water and dish detergent.¹⁰ Alternatively, you could also use bleach diluted with water (specifically, one cup of bleach to one gallon of water).¹¹

The slicker the surface, the easier it will be to clean—but mold may be wedged in more porous surfaces, making it difficult or impossible to remove.¹² In these cases, the moldy material may need to be discarded and replaced.¹³ For example, if you notice mold on porous materials like carpet, insulation, or ceiling tiles, that material should be thrown away.¹⁴

As you clean, you’ll want to keep some safety guidelines in mind:¹⁵

• Never mix bleach with other cleaning products, as it could create toxic fumes
• Always wear safety equipment (goggles, rubber gloves, and a N95 respirator¹⁶)
• Maintain proper ventilation by opening doors and windows while you clean

Experts advise calling professionals to clean the mold if it covers an area greater than ten feet.¹⁷

However, having professionals take care of your mold can be expensive. And the alternative isn’t much better. Who wants to spend hours scrubbing the mold off of their bathroom ceiling?

That’s why the best thing you can do to deal with mold is to keep it from growing in the first place.

How to prevent mold growth

Skip the expense of paying mold remediation professionals or the hassle of scrubbing it off yourself.

Prevent mold from growing by identifying and managing high moisture areas.

Identifying high moisture areas

The first step is identifying high moisture areas. As we mentioned earlier, you can identify high moisture areas by looking for signs of moisture damage.

The only thing is, if you’re already seeing moisture damage like buckling or water stains, chances are mold is already growing.

That means you’ll need something that can identify high moisture levels at its earliest appearance—before mold sets in. The best way to do this is to use a pinless moisture meter.

Unlike pin moisture meters, pinless moisture meters don’t require you to drive in pins and leave behind unsightly pinholes in your drywall or wood floor every time you want to take a moisture reading. Instead, all you have to do is press the pinless meter’s sensor plate against the surface you want to measure.

You can use pinless meters to measure the moisture content of your wood flooring or other wood products like furniture. You’ll want to make a note of any wood that measures over 20% MC as that’s the point at which wood can begin to grow mold.

You can even use it to check on the moisture levels of other materials like drywall, ceiling tiles, and carpet. The only thing is, pinless meters won’t be able to give you an absolute moisture content for non-wooden materials. Instead, they offer a relative mode, which, when switched to, allows you to get comparative moisture readings.

Even though relative mode won’t give you exact readings, it can still help you determine if a material has an excessive amount of moisture, or if certain areas of a material have higher moisture levels than other areas.

Let’s say you want to test the drywall behind your dishwasher.

To evaluate the moisture levels of those walls, you’d first need to measure a part of the drywall you know to be dry. If the drywall behind the dishwasher has a similar reading, you’ll know that it’s dry by comparative standards.

However, if the moisture level is much higher than the dry sample, it may be a hint that the drywall behind the dishwasher has moisture problems.

Managing moisture levels

Once you identify high moisture areas you can take steps to correct them before they get any worse.

You can do this by:¹⁸

• Using dehumidifiers
• Using air conditioners
• Using air purifiers
• Changing air filters regularly
• Turning on exhaust fans
• Removing damp materials
• Using mold-killing products
• Using mold-inhibitors

Your home should be safe from mold when the moisture content of your wood is less than 19%, your building materials measure close to your dry samples, and the humidity of your home is between 35-45%.¹⁹

Start preventing mold growth today

If you want to prevent mold growth in your home—or your client’s home—a pinless moisture meter is your new best friend.
While it can’t identify mold directly, it helps you identify areas with high moisture levels before mold growth occurs—which, in the end, will save you the time, effort, and money of removing mold from your home.

Visit our store to buy one of our high-quality moisture meters and start protecting your home today.

1. “Mold,” CDC, Sept. 26, 2024. (↑)
2. Ibid. (↑)
3. Ibid. (↑)
4. “What is an Acceptable Crawl Space Wood Moisture Content?” Atmox, May 10, 2021. (↑)
5. “What Homeowners & Renters Should Know About Mold,” Green Orchard Group, Nov. 10, 2022. (↑)
6. “11 Signs of Hidden Mold in the House and How to Find Them,” RPF Environmental Testing & Consulting Services; “Mold on The Floor? Here’s What to Do About It,” Green Orchard Group, March 17, 2022; “7 Warning Signs of Mold in Your Home,” Green Orchard Group, March 3, 2022. (↑)
7. “Mold,” CDC. (↑)
8. “Mold Allergy,” Mayo Clinic, June 21, 2021; “Mold,” CDC; “What Homeowners.” (↑)
9. “Lung Association Launches Healthy and Efficient Homes Project to Promote Healthy Indoor Air Quality,” American Lung Association, Aug. 15, 2023. (↑)
10. “How to Remove Mold From Wood in 7 Steps,” Green Orchard Group, Feb. 3, 2022; “What Homeowners.” (↑)
11. “What Homeowners.” (↑)
12. Ibid. (↑)
13. Ibid. (↑)
14. “Mold Clean Up Guidelines,” Environmental Health and Safety University of Florida. (↑)
15. “What Homeowners.” (↑)
16. “Mold Clean Up Guidelines and Recommendations,” CDC, Feb. 16, 2024. (↑)
17. “What Homeowners.” (↑)
18. “Mold,” CDC; “What Homeowners,”; “Mold Allergy.” (↑)
19. “How Much Moisture Does Mold Need to Grow?” My Pure Environment, June 30, 2021. (↑)