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Air barriers & water-resistive barriers

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Jun 13, 2014

WeatherTech is a family of high performance water-resistive barriers, air barriers, vapor retarders and waterproofing products. When used in conjunction with properly installed substrates, WeatherTech products provide a superior level of moisture protection for any structure. Available with various levels of permeance and installation options.

WeatherTech offers a full line of water-resistive barriers and air barriers to seal the building envelope, protect structural components, and promote healthier indoor air quality. Water-resistive barriers have one primary function: to keep incidental moisture from penetrating into structural components and the wall assembly interior.

Preventing moisture intrusion is extremely important, as moisture-sensitive building materials often consisting of gypsum, wood or light gage metal can become severely compromised when exposed to moisture.

Durable Moisture Protection

WeatherTech products provide continuous protection from incidental moisture. They address many of the concerns associated with sheet based building papers and wraps. Concerns related to lapping errors, tears or seam gaps are eliminated.

Liquid applied barriers outperform sheets goods because they are:

• Seamless: which eliminates water infiltration risk from horizontal and vertical seams.
• Continuous: which eliminates the risk of water infiltration from rips and tears.
• Direct Bonded: no need for screws, nails, staples, or other forms of mechanical attachment.
• Superior Weatherability: exposure to UV light and moisture during the construction cycle will not compromise their effectiveness.
• Are not dislodged by air pressures.

Proven Air Barrier

Air barriers isolate interior and exterior environments and limit the amount of air that can infiltrate a structure or leak out of it. According to the USGBC, structures consume 70% of the worlds energy with the majority lost from infiltration and exfiltration of air. The unregulated air flow can disrupt the efficient operation of a building’s HVAC system, creating strain on the equipment, thus leading to higher overall energy consumption, and an inconsistent environment for occupants. Heating and cooling costs can be impacted by 30% or more according to the Department of Energy. Because air contains water vapor, there is potential for unregulated air flow to create mold related issues within the wall components that can negatively impact air quality.

Historically, many building products such as sheet wraps and papers, wallboards, etc. were considered air barriers. Today, with increasing energy consumption and air quality concerns, their level of performance is no longer adequate. Parex USA’s WeatherTech line offers products that combine the water-resistive and air barrier features into one unbeatable offering.

Vapor Permeability

A key factor in moisture management of a building is understanding the atmospheric conditions impacting it. Moisture vapor is always present, with different temperatures and concentrations of moisture (relative humidity) in the air, creating a difference in vapor pressure from interior to exterior environments. Nature always tries to equalize this imbalance, which means that the water vapor will try to migrate from a location of higher concentration to one of lower concentration. This vapor drive flows from high pressure to low pressure across the wall assembly. The amount of vapor permeance, or breathablity required for a wall assembly varies depending upon climatic conditions and internal environmental requirements . The vapor drive from higher temperatures and pressures to lower plays a key role in determining the most appropriate type of membrane, permeance requirements, and proper placement within the wall assembly.

The most significant determining factor in proper selection of membrane type and position within the wall assembly design will be the geographic location of a structure, which determines temperature and humidity exposures and seasonal conditions. For most wall constructions in most climate zones, vapor permeable products like WeatherSeal should be considered.

Low permeance barriers: for some advanced wall designs, such as those for cold climate zones with metal studs, continuous external insulation only and no batt insulation between studs, a low permeance barrier coating like Weather Block on the exterior sheathing may be appropriate as an alternative to a vapor retarder on the indoor side of the framing. That is because in such designs, materials to the interior of the continuous insulation are all “warm in winter”. Some special hot-humid climate zone wall designs may also benefit from a low vapor permeance barrier. NOTE: WeatherBlock is not to be used when another vapor retarder is on the indoor side of the framing; a double vapor retarder can trap moisture in the wall.

In cold climate zones, a vapor retarder, like Parex USA’s WeatherBlock, stops water vapor leakage of conditioned air to the exterior. For hot, humid climate zones, it stops infiltration of hot humid air to the interior. For mixed climate zones, vapor permeable products, like WeatherSeal, should be considered.

The Weather Tech line offers products that accommodate the need for water-resistive barriers and air barriers with a variety of permeance ranges.

Vapor Retarder Location

The vapor retarder membrane - when desired - will be placed on the warm in winter side of the assembly;

A misplaced vapor retarder promotes condensation. If a vapor retarder is placed in the wall in a cold-in-winter location, vapor will flow toward it from the interior, be prevented from continuing out of the wall, and condense in the wall. WeatherSeal Spray and Roll-On and WeatherSeal Trowel-On are made to be vapor permeable for this reason.

Mixed Climates:

Walls in mixed climates are exposed to vapor drives from the inside in winter and from the outside in summer. In a mixed climate, the vapor retarder placement that could be right for summer may be wrong for winter and vice versa and that is why mixed climates generally should not have vapor retarders.

Cold winter climates:

Indoor air substantially contains more water vapor than the outdoor air as warm air can hold more water vapor than cold air. As the water vapor migrates towards the exterior, it can get concentrated and cold enough to condense and thus wetting materials in the wall. A material that retards the flow of vapor from the warm indoor air into the wall can prevent that condensation; that is why the vapor retarder is placed to the interior side of stud cavity insulation.

Hot Climates:

Some wall designs in the hot-humid climate zone can benefit from lower permeance barriers on the hot-in-summer side of wall. The idea is that this is the reverse of the cold climate situation. The vapor drive is from the outside toward the inside, sometimes called “reverse vapor drive”. However,