This addendum proposes clarifying requirements for the use of fully ducted return systems by recognizing that some spaces requiring a negative pressure relationship with the adjacent space require a fully ducted exhaust system rather than a return air system. This modification is made in Section 6.7.1, where the standard already has requirements for ducted return systems for spaces with a required pressure relationship. This addendum also proposes adding four additional spaces to meet the requirement for being fully ducted.