Masonry Magazine July 2009 Page. 32
AIR BARRIERS
It was once thought that water vapor through diffusion was the culprit in potential moisture problems in building design; however, experts discovered that air leakage provided a far greater ability to carry more moisture through miniscule holes, seams and other penetrations. Surprisingly, air leakage is capable of depositing several gallons of moisture each year into the system, 30 to 40 times greater than by diffusion. The use of an effective air-vapor barrier system can limit this moisture penetration through the CMU backup or sheathing and help eliminate the potential damage.
Differences between air, vapor and moisture barriers
WITH CLOSE SIMILARITIES between air, vapor and moisture barriers - as well as the fact that certain products or systems can be considered to be more than one type of barrier - confusion is bound to occur.
"Quite honestly, there are a lot of areas of the country where people aren't nearly as familiar with air-vapor barriers and their installation as you might think," says Christopher Bupp, technical services for Hohmann and Barnard, Inc.
Moisture Barriers
MOISTURE - or weather-resistive - barriers are intended to prevent non-vapor, liquid water from infiltrating the wall system. The International Building Code (IBC) requires moisture barriers to be integrated into the moisture management system for most types of wall designs. This system is effective in deflecting liquid, but once again- provides no protection against vapor diffusion or air leakage.
While vapor and air barriers can be considered moisture barriers, the opposite is not the case.
Vapor Barriers
ACCORDING TO the International Energy Conservation Code (IECC), a vapor barrier is: "A vapor-resistant material, membrane or covering such as foil, plastic sheeting, or insulation facing having permeance rating of one perm (5.7 X 10-11 kg/PA.s.m2) or less when tested in accordance with the desiccant method using Procedure A of ASTM E 96." The vapor barrier is effective in limiting moisture infiltration by means of diffusion, but typically not designed to effectively limit air leakage and the moisture accompanying it.
The IECC requires vapor barriers to be used in colder cdlimates, with a few exceptions, the International Building Code (IBC), by referencing the IECC, therefore also has the same requirement.
Air Barriers
BY CONTRAST, an air barrier is any material that restricts the flow of air under pressure through a building.
SANDELL'S AIR-TIGHTTM AIR & VAPOR BARRIER SYSTEM
Sandell's Air-Tight™™™ Air & Vapor Barrier system provides a superior and cost-effective building envelope for today's commercial structures. Control the unintended movement of air and moisture into and out of your building enclosure. Our sealant system essentially "wraps" the building, providing a barrier to water vapor that leaks in (from the inside in heating climates and from the outside in cooling climates), condenses and forms water, a key ingredient to corrosion and mold. Sandel's Air-Tight Sealing System also protects your buildings from suspended particulates, pollutants, dust, insects, odors - anything you want to keep out. Create a building envelope that delivers physical protection from weather and climate (comfort), indoor air quality (hygiene and public health), durability and energy efficiency with Sandell's high-performance products.