CSLB General Building (B)Finishes and Building EnvelopeMedium
A new single-family home has a conditioned floor area of 2,000 square feet. Under Title 24 Part 6 prescriptive standard design defaults, what is the maximum total fenestration (window) area typically allowed without triggering additional energy compliance measures?
- A400 square feet (20%)
- B200 square feet (10%)
- C500 square feet (25%)
- D300 square feet (15%)
Show answer & explanationAnswer & explanation
Correct answer: A. 400 square feet (20%)
Title 24's standard design default assumes total fenestration area equal to 20% of conditioned floor area. For a 2,000-square-foot home, 20% equals 400 square feet (2,000 x 0.20 = 400). Exceeding this default typically requires additional compliance credits or upgraded window performance to offset the added heat gain/loss.
Why the other options are wrong
- B. 10% underestimates the standard design default ratio.
- C. 25% overstates the standard default and would require compliance offsets.
- D. 15% is below the actual default fenestration percentage.
Title 24 Fenestration Area Default
Title 24's standard design assumes glazing area equal to 20% of a home's conditioned floor area; exceeding this default requires additional energy compliance measures.
- Default fenestration ratio is 20% of conditioned floor area
- Exceeding the default requires added compliance credits
- Higher-performance glazing can offset larger window areas
Memory trick: 'One-fifth for windows' — 20% is the default glazing share of floor area.