The Difference Between Vapor, Air and Weather-Resistive Barriers

"Do this, not that" is a common saying in the building industry. Controversial techniques for construction, outdated codes and incorrect applications have plagued the industry for decades. Building structures that are protected from the elements is pivotal to the future of residential design and construction. With increases in damaging weather events throughout the country, builders need to be up to speed on the various barrier options available for their next building project. Read on for a description of three common barrier options for your next project and learn more about their differences to best protect your project from the elements-both inside and out.

Vapor barriers 

Used to slow the movement of water vapor through a wall assembly, vapor barriers are a frequently misused barrier in many climates throughout the United States. Originally, vapor barriers were used to prevent wall and ceiling assemblies from getting wet during the construction process; however, they also often prevent assemblies from completely drying. A vapor barrier alone will not control airflow into or out of a building project, rather it exclusively controls the diffusion of moisture through wall assemblies. Unlike air and weather-resistive barriers, vapor barriers do not need to be continuous in a structure to provide protection. It’s complicated to know whether your next build needs a vapor barrier or not, as strategies for vapor barrier usage differ based on climate and seasonality. Unless you are building in climate zones 7 or 8 (extremely cold) you do not need to use a vapor barrier on your next build, because maintaining vapor permeability in building envelopes is important for mold reduction.

Air Barriers 

An air barrier is any material that stops air from getting into a building, including housewrap, windows and weather-stripping. While commonly confused with vapor barriers, air barriers restrict the movement of air into and out of buildings. While they are secondarily effective at stopping vapor from entering a wall assembly, they do not play any role in stopping the diffusion of vapor through a wall once it has entered. They are used primarily to stop air leakage and resist air pressure changes by maintaining a consistent indoor climate. Air barriers are durable enough to withstand knocks and handling during the construction process, penetrable to airflow, and able to provide a continuous envelope for the entire conditioned space. By controlling air movement, they provide great energy efficiency in buildings. 

Weather-Resistive Barriers

Integrated barriers, like LP WeatherLogic® Air & Water Barrier remove the need for multiple materials in an exterior wall assembly. High-performance air and water barriers resist air and water intrusion, which reduces the amount of moisture vapor in the panels. 

"Weather-resistive barrier systems lead the fight against moisture penetration," said Brian St. Germain, Director of OSB/EWP Quality and Technical at LP Building Solutions. "While exterior cladding can offer deflection, the exterior cladding is still technically not a moisture barrier. Therefore, the weather barrier is designed to keep water from seeping into the building enclosure."

LP WeatherLogic Air & Water barrier combines sheathing and weather-protective layers in a single panel that can be installed just like regular sheathing. Seams of the panel are securely taped with an advanced acrylic tape, featuring one of today's highest quality adhesives. LP WeatherLogic Air & Water Barrier panels feature an ASTM E96 tested vapor-permeable overlay permanently integrated into the panel, allowing water vapor to escape rather than getting trapped inside walls. 

Whether you’re building in Canada or Texas, integrating a weather-resistive barrier, like LP WeatherLogic Air & Water Barrier into your next project is a good bet.