Mold on joists in crawlspace

Mold is becoming a big issue on the joists in Tim’s crawlspace due to water pooling below the house. Now, Tim wants to know what to do about it before it causes some serious damage.

It’s pretty simple: Mold comes from moisture. The envelopes of most homes are tight, and easily trap moisture produced in bathrooms and kitchens. That’s why it’s important to have exhaust fans working and properly vented.

It’s especially important to take care of any moisture that accumulates under the house. For any crawlspace, you should lay plastic on the ground as a moisture barrier. That will significantly reduce the water that rises up from the ground.

Now, if you have intense moisture under the house, with no barrier, that will cause excees sweating and create the perfect breeding ground for mold and mildew.

While Tim’s crawlspace isn’t protected with a plastic moisture barrier, it does have foundation vents, which are helpful in preventing mold growth. But usually, they’re just not enough. You really need multiple methods to effectively keep moisture out of your home.

That’s why we recommend laying 6-mil plastic directly on the ground in the crawlspace. It will do wonders to prevent moisture from migrating off the ground and up to Tim’s joists, where mold can form.

Cut those pieces of plastic 8 or 10 feet wide so they are easier to install. Then buy a hygrometer, which is a simple digital instrument, to measure the humidity in the crawlspace. It shouldn’t exceed about 50 percent relative humidity under the home.

Want a bonus tip? Install an exhaust fan near the foundation vent that automatically turns on when it senses excess moisture and removes it instantly.

Listen to the embedded audio clip above for the full answer!

Read the blog from the Jan. 25 show and listen to the full broadcast here.

Further Learning:

Editorial Contributors
avatar for Danny Lipford

Danny Lipford


Danny Lipford is a home improvement expert and television personality who started his remodeling business, Lipford Construction, at the age of 21 in Mobile, Alabama. He gained national recognition as the host of the nationally syndicated television show, Today's Homeowner with Danny Lipford, which started as a small cable show in Mobile. Danny's expertise in home improvement has also led him to be a contributor to popular magazines and websites and the go-to source for advice on everything related to the home. He has made over 200 national television appearances and served as the home improvement expert for CBS's The Early Show and The Weather Channel for over a decade. Danny is also the founder of 3 Echoes Content Studio,, and Checking In With Chelsea, a décor and lifestyle blog.

Learn More