What Is a Good Humidity Level for a Garage?

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

If you want to keep your garage free of toxic mold and keep your tools from getting rusty, your goal should be to keep the humidity level below 50%.

When the amount of moisture in the air starts to climb past that mark, you’ll often start to experience negative effects.

For many homes, the garage is inherently a risk area for mold growth due to clutter and poor ventilation. If on top of those factors, you also fail to monitor the humidity level, it’s like sending the fungus a formal invitation to move in.

Here, we’ll take a closer look at garage humidity and try to answer some of the questions you may have surrounding it.

How to Check the Humidity Level of Your Garage

If you want to be absolutely certain that your garage’s humidity is where it needs to be, you’ll need to be able to measure it precisely. To do so, your best option is to invest in a digital hygrometer.

These devices, which are very affordable, use sensors to measure the amount of moisture in your indoor air.

If you purchase a hygrometer and use it in your garage, it’ll give you a reading of the exact RH (relative humidity) level.

If the number it gives you is below 50%, you’re in good shape and probably don’t need to take any action.

But if the RH is above 50%, you could be at risk for mold growth.

What Causes High Garage Humidity?

If your hygrometer gives you a high RH reading for your garage, it’s evident that something is causing there to be excessive moisture in the air. However, it often takes a bit of investigating to determine exactly where all that extra moisture is coming from, as there are a variety of potential sources that you may need to consider.

  • Plumbing leaks
  • Running home appliances in garage
  • Lack of windows/ventilation
  • Rainwater or melting snow on parked cars
  • Condensation on cold surfaces
  • Gaps or cracks letting rainwater in
  • Poor roof drainage letting rainwater in
  • Lack of garage door and wall insulation

Methods for Reducing Your Garage Humidity

As you can see, there are quite a few variables that factor into your garage’s humidity level. So, if you discover that the RH is above 50%, you may be unsure where to start. It’s important that you avoid procrastinating for too long; taking proactive measures to lower the humidity level is much more pleasant than having to deal with an existing mold colony. 

Rule Out the Biggest Problems

A good first step is always to eliminate the most serious potential issues. For example, inspecting any exposed pipes for water leaks is always a great idea. It’s also wise to inspect your garage for any openings that could be allowing water to regularly seep through. A simple way to do so is to wait for the next significant rainfall and immediately search for any unusual accumulation of moisture. If you find any, there’s a good chance that some kind of leak is nearby. Finally, it wouldn’t hurt to have your roof’s drainage inspected to ensure that everything’s in good condition and functioning properly.

Take Proactive Measures

Once you’ve eliminated the more serious problems as possibilities, you can start implementing some proactive measures and habits to reduce the garage’s humidity.

One easy option is to start wiping down your car after it rains before you leave it parked in the garage. If you’ve been running any appliances in your garage, such as the laundry machine, you may want to consider the option of moving it to another area of your home.

If that isn’t a practical option, it may help to start opening the garage door, either partially or all the way, whenever you’re running the appliance. If you’re running your laundry machine in a tightly sealed garage, it’s going to greatly increase the amount of moisture in the air.

Another effective method is finding a way to improve the garage’s ventilation. Whether that means regularly opening the window(s), running fans, or installing exhaust vents, it should prevent the air from becoming stagnant, which will bring the humidity level down.

Adding high-quality insulation would also be effective, as it would help keep outside moisture from getting in. Plus, good insulation would help the garage maintain a consistent temperature throughout the year, which would help to reduce condensation.

Use a Dehumidifier

If you want to take a more direct approach, or you’ve tried some of the above methods without much success, your best option may be to invest in a dehumidifier.

Many types of dehumidifiers are perfectly suited for the garage, and although this route won’t necessarily address the cause of the high humidity, it should at the very least be an effective bandaid for the problem.

With a dehumidifier, you’ll be able to set your preferred RH level, and it will work to consistently remove moisture from the air and keep it there.