Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.2

Inquiry

The project is planning the installation of high albedo and vegetated roof to cover 93.1% of the roof area (the remaining roof area consists of parapets and skylight openings). The high albedo roof consists of a membrane covered with white calcite ballast. The team had previously requested a CIR to ascertain that tests could be made on this ballast to ensure conformity with the reflectance and emissivity requirements to achieve this credit. The tests have been performed by a qualified laboratory as suggested in your CIR response dated 05/12/03. The results indicate that the emissivity criterion is respected but that the reflectance is .59 rather than the stipulated .65. According to previous credit interpretation rulings, namely CIR SS7.2 dated 1/21/2002 and CIR SS7.1 dated 12/05/2001, the lower reflectance can be compensated for by enlarging the area covered according to the formula specified in CIR SS7.1 dated 12/05/04. This would result in the following calculation: Required .65 x 75% + .05 x 25%=50 Design case .59 x 83.3% + .05 x 16.7%=50 Therefore in installing 83.3% of high albedo roof instead of 75%, the requirement would be satisfied. The question is the following; the team could increase the high albedo roof and reduce the vegetated roof to achieve 83.3% of high albedo roof (the roof composition is currently split as follows 78% high albedo and 15.1% vegetated roof for a total of 93.1% roof coverage of a combination of high albedo and vegetated roof). Reducing the quantity of vegetated roof however would reduce the amount of green roof available for occupant use, water retention, CO2 gas absorption and vegetation. Since the intent of the credit is to reduce heat island effects and that LEED 2.1 allows for a combination of 75% high albedo and vegetated roof , we would propose that covering the roof with 93% combination high albedo and vegetated roof would meet the intent. This provides an additional 10% roof coverage (93.1% versus 83.3%) with a combination high albedo and vegetated roof that would be required if all high albedo roof were utilized as shown in the design case equation above. Would this be acceptable?