The term "barrier system " refers to all of the barrier components, including membranes and/or building components and sealants. These materials make up the control layers.

There are four control layers:

• Water Control Layer (Weather/Moisture Barrier)
• Thermal Control Layer (Thermal Barrier)
• Vapour Control Layer (Vapour Retarder)
• Air Control Layer (Air Barrier)

Different components in the envelope system act to control the mechanisms of water, air, moisture and heat flow. These components are referred to as control layers. However, the National Building Code (NBC) refers to these layers as barrier systems.

When dealing with these systems it is helpful to remember what each layer seeks to control.

The Water Control Layer controls bulk water that moves by gravity and wind (above grade) and controls water moisture that moves by capillary action and osmosis (diffusion)(below grade).

The Thermal Control Layer controls the flow of heat through an assembly.

The Vapour Control Layer controls the movement of water moisture that is transferred by osmosis (diffusion).

The Air Control Layer controls the flow of air that moves because of pressure differences.

Envelope Control Layer/Barrier Location Choices

There are four above grade control layers/barrier systems:

The terminology for "control layer" and "barrier" or "barrier system" are used interchangeably. On-site the terminology will most commonly be "barriers". It is important to keep in mind that the main purpose for these barriers is to control the movement/flow of moisture, heat, vapour, and/or air.

This guide focuses on what the control layers do, how they work, and what criteria they must meet. The approaches/systems used to install these control layers

Control Layers Materials

A wide range of materials can be used for control layers. Some of these include but are not limited to the materials shown here. The sheathing membrane and moisture barrier both act as water control layers. The sheathing membrane is used above grade, and the moisture barrier is used below grade. Dampproofing is also used below grade.