This addendum clarifies and adds requirements related toindoor humidity and the building envelope as they relate topotential indoor air quality problems. Among other changes, itrevises the humidity control requirements currently describedin Section 5.10 by modifying the upper relative humidity limitand eliminating the lower limit. A lower humidity limit is nolonger included because the data supporting such a limit arevery limited and not entirely consistent. An upper relativehumidity limit is now a design requirement (not simply a recommendationas in the current standard) for mechanical systemswith dehumidifying devices and controls since highindoor relative humidity in conditioned spaces has been associatedwith conditions that can lead to microbial growth.Building pressurization requirements to minimize the infiltrationof moist outdoor air (which can cause condensation onbuilding surfaces during cooling operation) have also beenadded. In addition, the issue of condensation on cold interiorsurfaces and contaminant transport from attached parkinggarages is addressed.