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There are four (4) main control layers in the building envelope.

Those control layers are as follows:

• Water Control: Rain water, melting snow and ice and bulk water on the exterior of the building envelope must be directed down and away. The water control layer includes exterior finishes, eavestrough and downspouts, flashing and sealants.
• Air Control: Air tightness is an important part of high performance building envelopes. The air barrier can be anywhere in the building envelope assembly, though many designers in Canada favour air control layers to the interior to reduce heat loss through air leakage. An air barrier may be a roll-type fabric, air tight drywall, liquid applied or atomized spray.
• Thermal Control: The thickest layer of the building envelope will be insulation, or thermal control. Insulation can be installed in between structure cavities, in a continuous layer on the exterior or in deep layers under basement slabs and in attics. The other control layers all work to protect the thermal layer from water, air leakage and vapour accumulation.
• Vapour Control: The activity of people in a building creates moisture - steam from cooking and bathing, and moisture from breathing and plants. The vapour control layer is placed to the warm side of the building envelope to keep moisture laden air from building up inside structure or insulated assemblies. Vapour barriers may be roll-type plastic sheets, vapour retardant paints or smart fabrics.