U.S commercial building airtightness requirements and measurements

In 1998, Persily published a review of commercial and institutional building airtightness data that found significant levels of air leakage and debunked the myth of the airtight commercial building. Since that time, the U.S. National Institute of Standards and Technology (NIST) has maintained a database of measured airtightness levels of U.S. commercial building leakages, in part to support the development and technical evaluation of airtightness requirements for national and state codes, standards and programs. This paper presents the airtightness data from the NIST database and a summary of recent developments in U.S. codes and standards. The average airtightness of the 228 buildings in the database is 25 m3/h∙m2 at 75 Pa, which is a little over 10 % tighter than the average reported by Persily in 1998. This average commercial and institutional building airtightness is tighter than the average of all U.S. houses but leakier than conventional new houses based on a large database of U.S. residential building airtightness. The data are examined for trends related to size, year of construction, type of construction and climate. The paper also discusses recent code and standards developments including the adoption of a continuous air barrier requirement in ASHRAE Standard 90.1-2010 Energy Standard for Buildings Except Low-Rise Residential Buildings, various U.S. state building codes, and the proposed International Green Construction Code.