Rating System

LEED BD+C: New Construction, LEED O+M: Existing Buildings, LEED BD+C: Core and Shell, LEED BD+C: Schools

Rating System Version

v3 - LEED 2009, v3 - LEED 2008, v2 - Schools 2007, v2 - LEED 2.2, v2 - LEED 2.0

Inquiry

Our residential project is comprised of two multi-story towers that are connected on the ground floor with a single-story atrium that is sandwiched between the two towers. The sum of the two tower roofs equals 17,586 s.f. and makes up 70% of the total roof area. In order to comply with this credit and reduce heat islands, the two tower roofs are specified as a white TPO membrane that meets the emissivity and Energy Star requirements. We could easily achieve the credit requirement of 75% of the roof area by specifying white membrane for 1,254 s.f. of the 7,484 s.f. lower roof. However, in this case, we feel that having a high albedo lower roof would actually conflict with the intent of the credit. 97% of the curtain wall is glass, thus the towers would be subject to heat gain because the solar reflectance would project back up into the buildings. In addition, all of the residential units that face the atrium will have direct views of the roof which would expose the residents to glare. We propose to install a gray TPO membrane on the lower roof. This would not produce glare or contribute to as much heat gain as the white membrane, but still have a higher emissivity level than a standard black membrane. Given the circumstances, would you award us credit if the upper roofs are white and the lower roof is gray?