Figure 2-12 Up to one third of the insulating value can be installed on the warm side of the vapour retarder ( Keeping The Heat In, Chapter 2, Section 2.4.3) Illustration source: Keeping the Heat In, Fig. 2-12,Pg.20

The photo on this page is an example of terminology commonly used on-site, but this is not consistent with newer versions of the building codes. Depending on the assembly components, the vapour retarder may be placed closer or further from the interior of the home. Calculating the required inboard and outboard ratios for placement are covered in the advanced course.

Vapour Control Layer - How Does It Work?

The vapour control layer is engineered to only allow a specific amount of vapour to pass through it, depending on the air pressure, amount of time, and surface area of the control layer.

Criteria:

• Installed to the warm side of the insulation
• Impermeable to vapour diffusion
• Must cover as much surface area as possible
• Not necessarily resistant to air flow
• Durable during construction and over expected building life
• A vapour retarder material must have a permeance of 60 ng/(Pa· s · m2) or less