Moisture existing as a gas in air. Warm air can hold more water vapor than cold air. Water vapor in the air creates a pressure much like any other gas. Cold air has a relatively low vapor pressure, but warm air with larger amounts of water vapor has a greater pressure. The difference in pressures cause the vapor to do strange things such as penetrating building materials in the direction from high to low vapor pressure.

In need of a new Roof? Let the IRS help with the cost via Section 179.

X