Humidity Control in Green Building

Humidity in a Green Home 

Humidity is the amount of water vapor in the air. It is measured in three ways: absolute humidity, relative humidity, and specific humidity. See glossary

Humidity is increased or decreased by several mechanisms:

1. Air pressure differences cause air to move from high to low pressure. Moving air can either bring water vapor with it OR take water vapor from the home.

2. Humidity comes from many indoor activities such things as cooking, washing dishes, bathing, and doing laundry. Even a human body increase the humidity in a home.

3. Drafts can also affect the amount of humidity present so humidity problems are fairly common in older or less energy-efficient homes. 

When the amount of water vapor is held constant, when you

1. Reduce the temperature, the relative humidity goes up.

2. Increase the temperature, the relative humidity goes down.

Ideal Humidity

Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The ideal humidity level for homes is 45%.

Low Humidity

An indoor humidity level of less than 30% is too dry.

You will know your home's humidity is too low if static electricity is shocking you. Skin irritation and respiratory problems are other signs of low humidity.

Low humidity dries out the noses and throats of the home's residents. It causes scratchy dry throat, increased allergy symptoms, more frequent colds/infections, and even cracked fingers.

It also affects the wood in the home, which shrinks often damaging trim, hardwood flooring, and even wood furniture.  Sheetrock and paneling may crack from low humidity.

A home's heating system will lower the humidity. 

High Humidity

However, the reverse is true with a more energy-efficient home and a tighter envelope. 

The lack of air exchange coupled with humans and their activities can cause high indoor humidity.