The U. S. Army Corps of Engineers set up a specification that all its buildings should have an envelope air leakage less than 0.25 cfm/ft2 (1.27 litre/s.m²) under a test pressure of 75 Pa. This article describes how this air leakage rate has to be assessed, giving the test procedure for adjusting test pressure and measuring air leakage. The author indicates as a conclusion that air leakage below 0.30 cfm/ft2 (under 75 Pa) is often achieved without specific effort and proposes that a value of 0.1 (0,5 litre/s.m²) should be the level expected by 2010.