Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.0

Inquiry

We designed the building based on the understanding under version 1.0 that an Energy Star approved roof was sufficient to meet the credit. We chose a bare galvaulme roofing product for the majority of the roof for a number of reasons. It seems now that I can\'t get our supplier or Cool Roof Rating Council or anyone to confirm the 0.9 emissivity rating. Robyn Beavers at Cool Roof Rating Council recently wrote me to tell me that they haven\'t submitted bare galvalume to a third party testing agency. I have also found similar responses from other roofing suppliers. Ours stated that their bare galvalume is in the range of .86 so because the credit is listed to one significant digit it qualifies. If it was specified at .90 then we are splitting hairs. The issue is that we chose the bare galavlume to meet the City\'s criteria for a no maintenance roof. Some of the white and light grey coatings make it to 0.9. They didn\'t want a paint coating. I\'ve been designing cool roofs since the early 70\'s using bare galvalume for the benefits derived from its high reflectivity. A study done my Texas A&M published in August of 1983, Passive Design Handbook for Texas, verified the energy benefits of using a highly reflective roof and the radiant benefits of bare galvalume. I also read in version 2.1 where bare galvalume is referred to as an exception. Does that mean its a metal roof that works and meets the credit? I\'m totally confused now. The roof as designed should redirect 75% of the solar radiation normally absorbed by standard roofing materials, but it isn\'t going to meet achieve the credit? Isn\'t the intent of the entire LEED rating system to reduce finishes and reduce the impact of the building on the environment. The design of this roof using the galvalume does both. Its designed to be a 200 year roof and has sufficient reflectivity to reduce heat gain by 75%. The best rating I can find is 0.86 emissivity which does meet the 0.9 in terms of significant digits specified by cutomary scientific practice. Our team went to great pains to reduce the heat island effect. What isn\'t galvalue is a white epdm which meets the criteria entirely but doesn\'t cover 75% of the roof area. Bare galvalume in Texas is one of the most cost effective strategies for achieving high energy efficiency as a radiant barrier and because it is not painted it lasts virtually forever in the intense solar environment. If it doesn\'t, it is really short sighted from USGBC\'s viewpoint because it limits us to very expensive ceramic coatings, only light colored painted metals such as white which chaulk, fade and weather excessivley over time and highly reflective earthen materials or epdm type membranes. I believe the design of the roof of this project meets the intent of the credit with its design. I also can not get a firm determination from any of the resources listed in the LEED reference guide that will confirm or deny that bare galvalume meets this credit. Honestly, I had seen some emissivity criteria listing the emissivity at 0.9 when we made this decision, only now to find out that these manufacurers were using customary scientific practice by converting 0.86 to 0.9 emissivity.