WestCon Tribune

March 2007

February Review

Vapor and Moisture Control In Buildings

Presented By: Mike Cox, Techmarx Group

Lee Snyder, Vaproshield

Thanks to Westcon member Mike Cox and VaproShield representative Lee Snyder for an informative evening discussing vapor and moisture control in buildings.  Mr. Cox and Mr. Snyder managed to keep a lively audience involved in their presentation, Complete with demonstrations, samples and examples.

The presentation discussed the need for buildings to breathe. An air barrier system is an essential part of many modern building envelopes. Sheet applied air barrier membranes can provide liquid water resistance and air barrier  moisture protection to the building envelope.

High vapor permeability air barriers must be tear resistant, durable, resist high wind impact and water infiltration. Some air barriers ŇsealÓ a building, essentially minimizing air exchange while increasing condensation which can lead to poor indoor air quality, energy deficiencies and costly building damage.

WrapShield‰ is an air barrier designed to resist liquid water providing protection from mold, mildew and rot. WrapShield‰ combines the properties of an air barrier and vapor permeable membrane in one innovative, affordable product. These products can be used in conjunction with VaproShield,  products  both gentlemen represent.

In a moisture control overview, it was discussed how weather resistive barriers are part of an exterior wall system that is designed to protect building materials from moisture penetration. Moisture can penetrate through a variety of places including cladding joints, sheathing laps, penetration points and open joint reveals. Weather resistive barriers allow moisture vapor to escape, ensuring building materials remain dry, increasing building performance, decreasing maintenance costs and reducing the risk of moisture-related problems such as mold, mildew, rot and sick building syndrome.

 According to Joseph Lstiburek, PhD, PEng, in an ASHRAE Journal article, Moisture Control for Buildings, both air movement and vapor diffusion move moisture from the interior an exterior of a building enclosure into the building envelope. Moisture typically migrates from warm to cold (thermal gradient) and from more to less (concentration gradient). In cold climates, moisture flows from interior to exterior by passing through the building envelope

There are different types of weather resistive barriers including vapor barriers, vapor retarders, air barriers and air retarders. Not all air barriers are vapor barriers and not all vapor barriers are air barriers, however, all weather resistant barrier membranes must resist entry of liquid water into the wall system by providing a drainage plane. Attaching exterior cladding to furring strips or battens provides an air gap that improves drainage.

In accordance with ICC-ES AC38 Weather Resistant Barriers are tested for water resistance according to method AATCC 127-1998 which simulates typical vertical wall water resistance requirements on site.

The presentation discussed weather resistive barriers, moisture control, impact of climate conditions, vapor permeability, air permeability and air barriers, testing and solutions and test results.

Our thanks again to Lee and Mike for an outstanding and educational meeting experience.

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