|• Care for Pavers|
|• Cavity Wall Moisture Management|
|• Cleaning and Removing Stains Outdoor On Outdoor Pavers|
|• Mortar & Restoration|
|• Protecting Pavers From Stains|
|• Stone Veneer|
|Learn More About Sponsored Topics|
The Official Publication
of the Mason Contractors
Association of America
Understanding Air and Vapor Barriers
With moisture-related problems in both new construction and older buildings equally prevalent in the news, there is no doubt that air and vapor barriers should be a well used and understood tool in a designer’s bag of tricks. However, depending on a number of factors – such as the climate of the given location, the building materials used in the project, building codes, and other key design issues – the type of barrier and the appropriate location within the system’s structure vary greatly.
Moisture movement in the built environment
A properly designed and built masonry system will take into account these possible avenues for water infiltration. Masonry systems typically utilize some variation of moisture management – including the appropriate air space, flashing, weather-resistive moisture barrier, termination bars, drip edges, sealing seams, weeps, vents, and/or other tools – to effectively remove the majority of water infiltration. The combination of the cladding and moisture management system in the wall’s envelope provides the first protection against the environmental elements. However, this combination alone is no match against water vapor.
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
“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.
While vapor and air barriers can be considered moisture barriers, the opposite is not the case.
The IECC requires vapor barriers to be used in colder climates, with a few exceptions; the International Building Code (IBC), by referencing the IECC, therefore also has the same requirement.
While air barriers can be vapor permeable or vapor impermeable, there are several requirements of the air barrier system that must be met. An air barrier system must be able to resist live loads (e.g., wind pressure, HVAC mechanical loads, etc.) without failing, and the system must completely wrap the entire building envelope completely, without presenting any entry points for air leakage. Each air barrier component, assembly and the connections between them must be connected, from the roofing system to the below-grade structure, to resist these loads. A failure of any part of the system is a failure of the system as a whole.
While the 2006 IBC does not require an air barrier in exterior wall systems, experts suggest that we should expect a mandatory air barrier requirement with the 2009 IBC. Several factors play a part in this expectation.
Second – and more importantly – AHRAE 90.1 “Energy Standard for Buildings Except Low-Rise Residential Buildings” was updated in 2006 requiring the use of air barriers, which is adopted by reference by the IECC, which once again will be adopted by reference by the IBC in 2009.
Types of air barriers
Each type of air barrier product has specific characteristics that may provide benefits over another type for certain projects or climates; this very topic is grounds for another article unto itself.
Briefly, key design considerations in specifying the appropriate product include:
“From an installation standpoint, it really depends on the type of application as to which product makes sense,” Bupp says. “Also, with the different climates that we have in the United States, it really has to be determined by geographical area what types of products work best in any given application. I wouldn’t tell an architect firm in San Antonio, Texas, to apply a vapor barrier in the same area of a wall system as I would for a firm in Boston. Most designers understand that, but I still think it’s important to stress.”
If there is any doubt as to the appropriate material to choose for a particular project, your air barrier manufacturer can assist you in specifying the correct product.
The U.S. Department of Energy determined that 40 percent of the energy consumed to heat or cool a building is due to air leakage. However, according to a 2006 National Institute of Standards and Technology study, a properly specified and installed air barrier system can provide an energy cost savings of approximately 32 to 39 percent, with the largest savings going to buildings in colder climates. Also, due to this significant energy efficiency capability, air barriers can provide points toward a building’s LEED certification.
In addition, air barrier products themselves are getting greener, such as Hohmann and Barnard’s TextroFlash™ Green, a multi-purpose, flexible, self-adhered membrane manufactured from 45 percent recycled content, and TextroFlash™ Liquid, a VOC- and HAPs-free liquid air-vapor barrier.
Basic installation steps
Jennie Farnsworth is an Atlanta-based writer and editor.
|Last Updated on Monday, 03 August 2009 16:40|