Rating System

LEED BD+C: Schools

Rating System Version

v2 - Schools 2007

Inquiry

Our project is a 160,000 s.f. public high school renovation and 10,000 s.f. addition which intends to meet all prerequisite requirements in the new addition and the background noise requirements of ANSI Standard S12.60-2002 in the existing building. We are requesting a ruling regarding the requirements necessary to meet the intent of the prerequisite in the categories of sound transmission class (STC) and reverberation time (RT) in the case of non-compliant existing conditions. We believe that in some projects such as this one, the additional scope required to meet this prerequisite as written may be prohibitive, and prevent the project from achieving LEED for Schools in an existing building. The existing conditions of the building in STC, meet the requirement for all adjacencies except for classroom to classroom and classroom to restroom. The walls at these adjacencies have an STC of 45. This rating does not meet the ANSI minimum of STC 50 between classrooms and STC 53 between classrooms and restrooms. The existing classroom partition STC of 45 is regarded as a "good" degree of speech privacy where normal voices in adjacent classrooms are audible but unintelligible most of the time. This degree of acoustical isolation between spaces is commonly found in existing classroom environments, and the school in its current use has not reported any difficulties with excessive sound transmission between rooms. Complying with the STC required in the ANSI Standard will require additional scope involving the building up of the existing walls between classrooms and other use spaces, from the top of the existing wall to the underside of the deck, and the building of additional, isolated walls on the sides of the existing partitions in every classroom. We would like to suggest that this scope is prohibitive to the project, as it involves rebuilding approximately half of the existing building\'s interior partitions, demolishing the adjacent plaster ceilings, and extending/removing and reinstalling all equipment and furnishings along these partitions. Considering the difficulty involved in bringing the existing building up to the ANSI standard, and the lack of reported issues in the existing building regarding sound transmission, we believe that the existing sound transmission does meet the intent of the credit to allow effective communication in the classrooms. 12 of the existing classrooms and all new classrooms will meet the RT requirements. The remaining 43 classrooms have RT ratings ranging from 0.9-1.0 at 500-2000 Hz. These ratings do not meet the ANSI requirement maximums of 0.6-0.7 at 500-2000 Hz. In order to comply with the maximum value indicated in the ANSI standard, the most feasible required additional scope involves providing a dropped acoustical ceiling tile and grid on the entire ceiling surface, and extending all ceiling equipment and fixtures to meet the new surface level. We instead recommend improving upon the existing RT conditions in the classrooms that do not meet the ANSI standard by applying mineral fiber acoustical ceiling tiles directly to the existing plaster ceilings over 50% of the ceiling surface. This will decrease the RT rating to approximately 1 second at 500 Hz, 0.8 seconds at 1000 Hz, and 0.9 seconds at 2000 Hz. Actual RT will be slightly less when the room is fully occupied. Considering the difficulty involved in bringing the existing building up to the ANSI standard, we believe that the proposed scope and improvement upon the existing RT rating does meet the intent of the credit to allow effective communication in the classrooms.