We request clarification on the circumstances under which CO2 monitoring in non-densely occupied spaces can be employed in lieu of direct outdoor airflow measurement devices. The project is a hotel facility registered for NCv2.2. Common areas such as the lobby, corridors and meetings rooms are ventilated by roof top units, and guest rooms are served by individual VPAC systems installed in the perimeter wall. The project team is considering how the credit criteria can be applied to the guest rooms. Per the credit requirements, these spaces would qualify as non-densely occupied and therefore be subject to the requirement for a direct outdoor airflow measurement device. A 1/16/2007 NCv2.2 ruling addresses a similar situation in a residential project, and suggests that two design scenarios might allow for meeting the requirements in these spaces: 1) Make up air could be supplied via a pressurized corridor in a manner conducive to monitoring at the large AHU serving the space. 2) It may be possible to monitor OA that is introduced directly through a conditioning unit. The first scenario is not possible because of fire safety codes that prohibit use of the egress corridor to supply make-up air for the guest rooms. A review of available air flow monitoring products for these small HVAC systems indicates that the second scenario is also not possible due to a lack of commercially available options. The project team is willing to install CO2 monitors in each guest unit to ensure that adequate ventilation is maintained for occupant comfort and well-being. Another recent CIR filed under NCv2.1 seems to support this methodology and states that "use of CO2 sensors in non-densely occupied spaces that meet the requirements for densely occupied spaces under LEED-NCv2.2, in lieu of direct outdoor airflow measurement, meet the intent of EQc1." However, it is unclear if this ruling is specific to projects registered under NCv2.1 that are seeking to employ v2.2 credit criteria, or if this compliance path is available to all NC projects. Can an NCv2.2 project utilize CO2 monitoring in non-densely occupied spaces as well as densely occupied spaces to meet the intent of the credit? If not, would monitoring the volume of air traveling through the exhaust system in each guest room or continuously monitoring the damper position of each VPAC system be appropriate?