In this video This Old House plumbing and heating expert Richard Trethewey teaches Kevin O’Connor what he needs to know about handling wet basements.

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Plumbing and heating expert Richard Trethewey explains basement moisture control to Kevin O'Connor. After discussing some of the most common causes of wet basements and their consequences, Richard shows Kevin some methods for controlling them. Richard then explains how dehumidifiers work and how they may be the best option.

Wet Basement Woes are Hardly Universal
Believe it or not, only about 40 percent of homes in the U.S. have basements. However, of those homes that do have basements, 60 percent have moisture problems. These problems may include rainwater not dispelling far enough from the eaves, groundwater soaking through the foundation, or moisture vapor making its way into the home. And despite not everyone having these issues, everyone who does dislikes them.

Why Wet Basements are a Problem
Make no mistake, wet basements can be a problem—especially when it comes to mold. Mold needs three things to grow: the right temperature, moisture, and organic matter. All of these conditions exist in the average wet basement, and mold can grow, causing damage and health concerns.

When Grade is an Issue
Sometimes, the issue is that the grade pitches back toward the home. In these cases, there are two options: regrade the property or install French drains around the outside of the building. Both options will route the water out to the yard and prevent it from soaking into the basement.

Also, adding downspout extensions to the gutters may allow the rainwater collecting on the roof to drain further away from the home. This can protect the foundation and prevent water from soaking the ground around the basement walls.

When It’s Groundwater or Vapor
Most of the materials used to construct foundations aren’t waterproof. Poured concrete, concrete blocks, and fieldstone are porous and will allow water to get into the basement. The option here is to seal the walls with hydraulic cement or epoxy paint. Another option is to use plastic sheeting to keep the moisture from making its way into the basement.

One other option that’s popular in basement spaces is a floating subfloor with a plastic backing. These hard plastic backings have feet that hold them up off the floor and allow water to pass underneath them without soaking the USB on top.

If It’s Humidity
Not all humidity is bad (in fact, humans are most comfortable around 30 percent humidity). However, high humidity levels in a basement can be a problem. For these conditions, the best solution is often a dehumidifier.

Dehumidifiers are essentially low-powered air conditioners. They have cold coils on which moist air condenses. Once it condenses, it falls into a tank that the homeowner has to empty. They also have hose spouts that act as drains, and some even come with pumps that push the condensed water out of the unit and into a drain.

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About Ask This Old House TV:
From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. ASK This Old House helps you protect and preserve your greatest investment—your home.

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Easy Solutions for a Damp Basement | Ask This Old House
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