Insulation

Why:
The objective of insulation is to seal conditioned areas from air penetration, reduce heat transfer (R-value), and keep moisture out. In other words: insulation is needed to keep conditioned areas separated from unconditioned areas. It is important to insulate well (picture right), in cold and warm climates.

How:
The building envelope is made up in to two layers:
1--The air barrier is made up of drywall and sheathing, to stop air leaks. It also keeps moist air from penetrating into insulation material, which can dramatically reduce the R-value, damage the building materials, create mold, and affect the health of the inhabitants
2--The insulation barrier is made up of insulation material (batts or loose fill) that insulates against heat transfer, but does NOT seal against air leakage.

Moisture will dramatically reduce the R-value (insulation capacity/value/rating) of any insulation material.

To protect against rain or moisture, a continuous vapor barrier should be properly installed within the wall system of the home. Have a well-functioning drain system between the inside and outside wall, and around the house have a well-functioning (French) drain system and a sloping ground to keep the rain away from the foundation and walls. Also, have a sill gasket on top of the foundation wall to prevent moisture from wicking into the framed wall from the concrete foundation via capillary action.

Where:
Insulation is needed at the thermal boundaries of the building envelope, including between framing members, called bridging. Areas that need insulation are:
-Walls
-Attics
-Ducts
-Windows
-Foundation