Understanding the science of energy movement can help designers and builders predict how heat, air, and moisture will travel through the building envelope. Proper planning and detailing within these rules can reduce building failures and help improve a home’s energy performance, comfort, and durability.
Heat Flow
- Heat is energy produced with the motion of molecules.
- Heat flows from warm to cold.
- The temperature difference between two adjoining surfaces drives the rate of heat exchange.
Airflow
- Air flows from higher to lower pressure.
- Heated air moves moisture.
- The amount of air in equals that of air out.
Moisture Movement
- Moisture flows from warm to cold within the same medium.
- Moisture flows from more to less.
- Things always get wet and must be allowed to dry.
- Air pressure induces flow of moisture-laden air.
