Inclusion of cool roofs in nonresidential Title 24 prescriptive requirements

Total savings range from 1.90 to 8.30 $/m2 (0.18-0.77 $/ft2) with TDV, and from 1.70 to 7.10 $/m2 (0.16-0.66 $/ft2) without TDV, across California's 16 climate zones. The typical cost premium for a cool roof is 0.00-2.20 $/m2 (0.00-0.20 $/ft2). Cool roofs with premiums up to $2.20/m2 ($0.20/ft2) are expected to be cost effective in climate zones 2-16; those with premiums not exceeding $1.90/m2 ($0.18/ft2) are expected to be also cost effective in climate zone 1. Hence, this study recommends that the year-2005 California building energy efficiency code (Title 24, Part 6 of the California Code of Regulations) for NR buildings with low-sloped roofs include a cool-roof prescriptive requirement in all California climate zones. Buildings with roofs that do not meet prescriptive requirements may comply with the code via an “overall-envelope” approach (non-metal roofs only), or via a performance approach (all roof types).