full screen background image

Basement Moisture Causes and Solutions


Basement Moisture Causes and Solutions

The University of Minnesota Housing and Technology Department performed a comprehensive study on the problems, causes and solutions to basement water intrusion and moisture. Here is some of the information published by them. This is a great source of information.

A problem that can damage your health and home

Water problems in existing basements are very common, but often are not understood or properly treated. In a basement that is seldom used and separate from the living spaces above, this may not present a great problem. However, most basements are connected to the rest of the house through ductwork or other openings. In addition, basements are increasingly used as finished living and bedroom spaces. In these cases, moisture problems are not only annoying and uncomfortable, but can lead to significant health problems. Molds and mildew can grow in damp carpets and beneath wall coverings. Finishing a basement without first dealing with the moisture problems can result in making health conditions worse and lead to significant damage as well. Basement water problems are solvable, but there is a cost to doing it right.
Understanding the problem

To correct basement moisture problems, it is necessary to understand where the water is coming from, and what mechanisms permit it to enter the basement.

There are just three sources of moisture:

1.Liquid water from rain or ground-water.
2.Interior moisture sources such as humidifiers, unvented clothes dryers, bathrooms, and cooking, as well as the moisture in concrete after construction.
3. Exterior humid air that enters the basement and condenses on cooler surfaces.

Moisture is transferred from the outside of the building to the basement interior by four mechanisms:

1.liquid water flow
2.capillary suction
3.vapor diffusion and
4.air movement.

Sometimes problems are traced to poor construction with cracking, settling foundations. In many cases, however, houses and basements can be structurally sound but are often not properly built to handle water drainage. Failure to slope the ground surface away from the foundation or lack of a good gutter and downspout system is common. Missing or nonfunctioning subsurface drainage systems are also found relatively frequently. A systematic approach can solve all of these problems.

This publication briefly describes moisture sources, moisture movement mechanisms, and typical basement moisture problems. Then, a step-by-step process for addressing each problem is presented along with several detailed approaches to solving the problem.


Water trickling out of walls
Standing water on floor
Saturated base of concrete block walls— a ring of dampness
Damp, humid air
Condensation on cold walls and floor in summer
Odor, mold, and mildew
Deterioration of carpet or wood
Rot and decay of wood headers, joists, sill plates, and columns
Staining and blistering of wall covering
Efflorescence, spalling of concrete or masonry

Basement moisture sources

Rain and groundwater

In a one-inch rain, 1,250 gallons of water fall on the roof of a 2,000-square-foot house. Without proper grading, gutters, and downspouts, some of this water flows into the basement. The below-grade water table can also rise due to flooding or seasonal site conditions. This is why sandy soils use drain tile systems.

Interior moisture sources

Moisture is generated inside of basements from people and their activities. Common sources are humidifiers, unvented clothes dryers, showering, and cooking. A finished basement increases these activities. Moisture contained in the concrete from construction is another source. In a typical house, this can amount to 0.2 gallons per square foot of wall, and 0.1 gallons per square foot of floor. It may take many months or even years for a new house to come into equilibrium with its environment.

Ventilation with humid outside air

Open basement windows for fresh air in the summer. If the outside air is warm and humid, it will condense on the cool basement wall and floor surfaces. Many homeowners see this and believe they are experiencing basement wall leakage, when in fact the accumulated water is from condensation.