When designing a new building enclosure, or retrofitting an existing building enclosure to improve energy efficiency the designer must make value decisions on when there is value in spending additional money to exceed minimum energy code requirements in order to achieve the best return on investment.

The 2010 ASHRAE 90.1 code has increased the prescriptive R-values for buildings and requires continuous insulation and a continuous air barrier, but without a defined allowable whole building air leakage rate. A whole building air leakage rate of 0.4 CFM/sf. @ 75 Pa is generally accepted for a building with a continuous air barrier. Experience with USACE projects has shown, however, that an air barrier performance of 0.25 CFM/sf @ 75 Pa is achievable with additional attention to detail during design and construction.

This paper will present a parametric energy model study for a new construction prototype commercial office building and for the retrofit of an existing prototype commercial office building (ASHRAE 90.1-2004 compliant) in Zone 3, 4, and 6 climates. Air leakage rates will be modeled for normal construction without air barrier requirements, for minimum air barrier construction (0.4 CFM/sf @ 75 Pa), and for enhanced air barrier (0.25 CFM/sf @ 75 Pa). Code minimum insulation levels will be modeled, along with various levels of enhancement over minimum requirements.