How to combat too much humidity in a garage

Beautiful gray stone house

Whether you use the garage for projects, as a home gym, or anything else, you want the air to be comfortable, not hot and humid or cold and clammy. Neither is comfortable, and both are a source of mold, mildew, and corrosion on metal inside the garage. How these spaces become damp is simple – the region dictates the conditions and if you are by the sea, a lake, or in a hot and humid setting, the garage is likely going to reflect what's going on outside.

Sources for Humidity

How does a garage get so humid? Here are some common causes:

  • There are cardboard boxes filled with things that you no longer use. Cardboard accumulates moisture and odors. Use plastic storage bins.
  • The garage isn't insulated.
  • The garage door is insufficiently weathertight or uninsulated
  • There is firewood inside and logs contain a lot of moisture.
  • The washer and/or dryer are the garage. Be sure the dryer's exhaust hose and dryer vent are working properly and unobstructed.
  • There are various types of liquid in containers
  • The garage floor is sealed, but with an epoxy paint
  • The car is stored during the winter in the garage and accumulated snow or ice melts from within the wheels or underside. This holds true if you've driven a car in the rain.
  • There is a floor drain with a catch basin, and it must be kept free sand, stones and debris. Still, it will remain a source of humidity and possibly odors from standing water.

Clearly, not all garages have all of these sources for humidity, but you must determine where yours originates. Then, set a hygrometer in the garage for 24 hours. This is a gauge to help you measure levels of moisture, and though it will always be higher in the garage than in the house, it's good to keep track.

In addition to the hygrometer, an effective way to track the humidity level in your insulated but weathertight garage is to have windows installed in at least one wall. Then, look at a lower corner to see if there is ice or condensation when the outdoor conditions are damp or humid.

Reducing the amount of humidity

If you have found your garage to be damp, there are two basic elements that need to be in place if you want to adequately resolve your humidity problem. The first is that your garage should be insulated. If not, it will be nearly impossible to get humidity under full control and conditions comfortable inside the garage. In cold climates, heating the space often works, and a wood stove is an affordable solution.

The second element is your garage door, really your "fourth wall". This has to be insulated and weather tight, and offer a thermal resistance factor of at least R-12. This is done through the use of doors insulated with polyurethane foam that's injected between the door walls.

Another issue to examine are weatherseals. For example, is there any exterior perimeter weatherstripping? Does it overlap the top and sides by at least 1 ½ inches? Does the bottom weatherstripping effectively block rainwater? Does the threshold slope towards the outside of the garage? The goal is to find all entry points for humidity, both in summer and in winter.

Begin with a list of the sources to eliminate and how much humidity you will tolerate. We are going to assume the door is insulated; otherwise, all other steps are pointless.

Basic Measures

If you are not using the garage for long stretches of time, you can plan to make it comfortable when you will put it use by turning off the heat, and opening your garage door an inch or two to let the humidity out around 45 minutes before you need the space. If there are doors and windows, open them to get air flowing. The humidity will escape and even faster if you set up a fan.

Picture of a home dehumidifier

Another short-term option is to install a home dehumidifier. Run this at its maximum level for at least a full day to decrease humidity by 5 to 8 degrees.

If it is a long-term measure because you use your garage space more often, there are commercial dehumidifiers that will integrate into a heating system. You will find many options at many price points.

Empty garage with a white garage door

You can purchase a device, 9 x 6 ½ x 4 in. to vent humidity out of the garage via a duct in the wall.

You can also opt for a vent in the garage door. They are not all that effective where humidity control goes, but they can work well at preventing odors.

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