According to California Title 24, what is the minimum aged solar reflectance requirement for cool roofs on steep-sloped residential buildings in Climate Zone 2?
Correct Answer
B) 0.20
California Title 24, Section 150.1(c)1B requires cool roofs on steep-sloped residential buildings in Climate Zone 2 to have a minimum aged solar reflectance of 0.20 and thermal emittance of 0.75. This requirement helps reduce cooling energy consumption in California's hot climate zones.
Why This Is the Correct Answer
California Title 24, Section 150.1(c)1B requires a minimum aged solar reflectance of 0.20 for cool roofs on steep-sloped residential buildings in Climate Zone 2. This value was set to balance energy savings from reduced cooling loads against the practical limits of roofing materials available in that climate zone. The requirement also pairs with a thermal emittance of 0.75 to qualify as a cool roof.
Why the Other Options Are Wrong
Option A: 0.30
0.30 is a higher reflectance value used in other climate zones or for low-sloped roofs where more aggressive solar reflection is required. Applying 0.30 to steep-sloped residential roofs in Climate Zone 2 overstates the Title 24 requirement for that specific combination.
Option C: 0.15
0.15 falls below the minimum required reflectance and would not qualify a steep-sloped residential roof in Climate Zone 2 as a code-compliant cool roof under Title 24. Roofs at this low reflectance absorb more solar heat, increasing cooling loads.
Option D: 0.25
0.25 is between the correct answer and the higher 0.30 value. While it may seem like a reasonable middle ground, it does not match the specific Title 24 requirement of 0.20 for this roof type and climate zone combination.
Memory Technique
Think of '0.20 = 20%' and associate it with the phrase 'steep slopes need less reflectance — 20 is plenty.' The steeper the pitch, the less direct sun hits the surface, so a lower reflectance threshold (0.20) is sufficient.
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