A previous USGBC Ruling for a multi-family building accepted tracer gas testing of a 10% sampling of unit-to-common area interfaces as an adapted Prerequisite requirement, wherein common areas are non-smoking and dwelling units, in which smoking cannot be controlled, are the "smoking rooms". Most commercial and institutional buildings avoid the issue and cost of tracer gas testing by being smoke-free as a matter of policy. As the previous Ruling recognized, multi-family buildings present a different usage scenario. Testing even a 10% sampling of the units according to the ASHRAE-129 standard can add a significant cost to a project budget for a procedure that is normally not done for this building type. Yet since it is part of a LEED Prerequisite, the cost is unavoidable for any project of this building type seeking LEED Certification. Firstly, can less than a 10% sampling be accepted for the Prerequisite requirements? Secondly, we propose the following method for meeting the intent of this prerequisite with an alternate testing protocol that we believe fulfills the mission of ASHRAE-129 without all of its added complexity and associated cost: 1) Collect outdoor measurements for temperature, relative humidity, carbon monoxide and carbon dioxide. 2) Monitor for carbon dioxide and other parameters to establish a baseline for selected apartment units. 3) Release carbon dioxide into the selected unit, one unit at a time, until it reaches a sufficient equilibrium. 4) Monitor for carbon dioxide in adjacent units and areas. 5) Repeat on remaining units or 10% of the building. 6) Calculate the air change effectiveness. 7) Collect relevant documentation on building systems and history. 8) Provide preliminary debriefing upon completion of calculations. 9) Provide final report inclusive of all data collected, findings, discussion of significance and a tracer gas analysis report. Please comment as to whether the above methodology is acceptable, and state what minimum unit sampling (ie 10% or less) is required to meet this Prerequisite.