Masonry Magazine July 2007 Page. 37
SCAFFOLD PLANK
LAMINATED OR SOLID SAWN
During the past several years, energy efficiency has been a top priority in designing and constructing building exterior walls. Although model energy conservation codes have been in existence for many years, their adoption by various states and municipalities has made energy-efficient design mandatory.
Increasing energy efficiency in the exterior walls involves the use of more insulation (higher R-value) and various measures to reduce energy loss from infiltration/exfiltration. However, the use of more insulation increases the potential for condensation within the wall assemblies as the temperature differential between the inner and outer surfaces of the walls increase. For this reason, the proper use of vapor retarders and air barriers is critical for proper performance of exterior wall assemblies.
The proper use of vapor
retarders and air barriers is
critical for proper performance
of exterior wall assemblies.
In addition to issues with energy efficiency and moisture condensation, the design of any exterior wall assembly also should include provisions for controlling penetration of moisture in liquid form (i.e., rain). In barrier-type walls, such penetration is resisted entirely on the outer surface of the wall (such as a non-drainable EIFS system). However, in drainage-type systems (such as a masonry cavity wall), resistance to water infiltration is primarily provided within the wall assembly through the use of a weather-resistive barrier.
This article summarizes the functional aspects of vapor retarders, air barriers and weather-resistive barriers.
Air Barriers
THERE ARE MANY FACTORS that produce differential air pressure between the interior and exterior of a building. These factors include stack effect on tall buildings, mechanical pressurizations/depressurization, and wind.
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July 2007
Masonry 35