Musty Crawl Space

Q: My home occasionally has a musty odor, and I’m worried it could affect my health or the health of my home. I suspect the vented crawl space is to blame. Is there an easy fix?

A: This issue can usually be fixed by stopping the water that supports the biological growth emitting the musty smell.

Peek into your crawl space. Depending on the layout of your house, you might be able to see quite a bit without crawling inside. If you notice standing water, you will need to figure out where it is coming from. Explore the crawl space to determine if the water is from a plumbing leak, groundwater or a recent rain event. If there is no plumbing leak or obvious groundwater problem, head outside to find other ways water is getting in.

From the exterior of the house, make sure that the soil touching the foundation walls slopes away from the house. You never want standing water next to the foundation, and you especially don’t want it pouring in through a foundation vent.

Next, walk around the house looking up. Are there gutters? Are they clear of debris? Are they connected to each other and secured to the house? Make sure that the gutters are attached to a downspout. Are the gutters and downspouts adequately sized (e.g., does rainwater flow in the gutters or over them like Niagara Falls)? Is there a downspout extender that takes the water at least five feet away from your house? Check for clogs in underground drainpipes with a water hose.

It also wouldn’t hurt to look into the crawl space after a rainstorm to see if there is a swimming pool beneath the house.

The solutions to liquid water vary. Some homes may need more soil to make the ground slope away from the house or gutter extenders to prevent miniature ponds at the end of each downspout. Others may need protection around crawl space vents to keep rain from flowing inside. More intense grading, a drain around the perimeter, a sump pump to remove groundwater buildup, or a plumber to fix a long-term leak are other possibilities. Bigger issues are best solved by a trusted contractor.

Once liquid water has been addressed, you can move on to other sources of water. The soil under nearly all North Carolina homes has moisture in it. If the crawl space floor is dirt, you should install a vapor retarder throughout the entire space. The term may sound technical, but the material is not: six mil or thicker plastic on a roll. Seams should be overlapped a minimum of 12 inches and taped. The vapor retarder should also extend at least six inches up the foundation wall and piers. Crawl spaces that have slightly thicker plastic and are secured to the ground minimize potential damage from telecommunication workers, plumbers, etc.

While you’re going through the trouble to minimize moisture, make sure you’re not providing housing to wildlife — vents should be properly screened and access doors secured. Funny smells can come from rotting carcasses and animal droppings.

Limiting the moisture that feeds the musty odor will also help keep the wood floor structure drier and lessen the need for future repairs or replacement. Eliminating standing water next to the brick or concrete block foundation wall will ensure longer durability of the structure as well.