The fact that many vapor barriers also retard or eliminate airflow sometimes causes confusion about the functions of the ABS and vapor barriers. The function of a vapor barrier is to control water/vapor diffusion and reduce the occurrence or intensity of condensation. As such, a vapor barrier has one performance requirement: it must have the specified level of vapor permeance and be installed to cover most of the area of an enclosure.
That being said, vapor control systems are either vapor permeable or impermeable membranes. Determining which type you need primarily depends on climate and wall design.
There are a wide range of products and systems available today that employ formulations suitable for any climate. These will protect buildings from water infiltration in high-rainfall regions, as well as from water vapor drive and unwanted air movement. (Example: STO VaporSeal®) Fluid-applied, vapor-permeable building membranes are especially versatile, and may be used under a variety of mechanically attached claddings, including cement board, wood, vinyl, brick, stone and metal panels.
Providing thermal comfort without overspending on excessive space conditioning costs is also one of the primary requirements of today’s building designs.. Therefore, thermal control is an important aspect in almost all buildings. Understanding heat transfer and the temperature distribution through building materials and assemblies is critical for assessing energy use, thermal comfort, thermal movements, durability, and the potential for moisture problems.
The key components for controlling heat flow in building walls requires insulation layers that aren’t penetrated by thermal bridges, an effective air barrier system, good control of solar radiation and management of interior heat generation.
So, in conclusion of our three-part series, a “clever” wall (we’ll even venture to say a “smart” wall), needs resilient design components that control air, moisture, vapor and thermal conditions. Get the wall right and it can make all the difference in creature comfort, energy efficiency and economics. Whether you’re retro-fitting or building from scratch, wall systems that can provide all four key controls are what you want.