What is Humidity and How Does Moisture Get Trapped in Tight Spaces?

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What is Humidity?

Humidity, water vapor, moisture, steam. They’re all the same. They are all one form of water. Humidity is an invisible gas. It is present in varying quantities in nearly all air.


Scientists describe this force as “vapor pressure.” It is often a very powerful force indeed. It can act independently of the flow of the air, which holds the moisture. Vapor pressure can force moisture easily through wood, plaster, cement and brick. Right through most of the materials we use to build our homes. That is exactly what happens when moisture seeks to escape from the humid air usually found inside your home to the drier winter air outside.

More Moisture Trapped in Less Space

Certain building materials stop water vapor. Glass is one of these. Also on this list are some varnishes, paints, tiles, plastics, & wall coverings. Vapor barrier insulation is designed specifically to stop the escape of water vapor and protect the insulation in your walls from the ravages of water.

Increased use of these “moisture trapping” materials in the last few years has created the modern “tight” home. Moisture created by bathrooms, kitchens, laundry rooms, and occupants no longer flows easily to the outside. Modern insulation and construction that keep cold air outside also keep moisture in. So, it is very easy to build up excessive and even harmful moisture levels in such homes. AMERICAN BUILDER magazine calls the problem a combination of many causes that build excessive moisture in the modern home.

First, more washing, more bathing, more showers, more appliances, more gas furnaces–all pour more water vapor into homes than in former years.

HEATING & VENTILATING magazine provides builders with reference data for sources of water vapor.

For instance, cooking for a family of four adds 4.5 pounds of moisture per day to a house. Each shower contributes half a pound; weekly laundry 30 pounds; human occupancy 6 to 9 pounds; dishwashing 1.2 pounds.

All this moisture MUST eventually escape from your home. So you see that the modern family of four can easily release 150 pounds or more than 18 GALLONS of water per week into the air in their home! And houses with no basements have even further moisture problems.

What can we do to reduce all this moisture in our homes?  Read our next post to learn about 7 practical steps to reduce humidity in your home!