Is Your Basement Dry Enough to Finish?

Where basement moisture comes from

• Rain and groundwater. Without proper grading, gutters and downspouts, some rainwater flows into the basement. The water table can also rise with flooding or seasonal site conditions.
• Indoor sources. Humidifiers, unvented clothes dryers, bathrooms and cooking.
• Condensation. Warm, humid outside air condenses on cool basement walls and floors.
• New concrete. It gives off water as it cures, in a typical house about 0.2 gallons per square foot of wall and 0.1 gallons per square foot of floor.

A leak, or condensation?

They can look the same. UMN Extension notes that many homeowners see condensation on basement walls and believe the walls are leaking. A ring of dampness at the base of a wall is a different thing: water drawn up through the concrete from below. Ask which one it is before anything is framed.

Start outside, with the low-cost fixes

UMN Extension advises doing the easy, low-cost things first and controlling the source of the moisture:

• Grade the soil so it slopes away from the foundation at least 1 inch per foot, for at least 6 feet.
• Have at least one downspout per 50 feet of eave.
• Extend downspouts so they discharge at least 4 feet beyond the wall.

What does not fix it on its own

• UMN Extension says a dehumidifier can help reduce the symptoms of humidity and odor, but it does not solve the problem.
• A membrane or coating on the inside of the wall, without drainage, generally won't solve the problem in the long term.

Why it matters once the basement is finished

UMN Extension warns that mold and mildew can grow in damp carpets and beneath wall coverings, and that finishing a basement without first dealing with moisture problems can make health conditions worse. And water found after a basement is finished means taking finished walls back down.

Questions to ask at the on-site estimate

• Where is the moisture in this basement coming from: outside water, indoor air or the concrete?
• What has to be fixed before framing, and is it on the written estimate?
• What happens to the price if water is found behind a wall later?

The on-site estimate is the moment to ask, standing in the basement, where any damp corner can be seen.