A residential building in California has a conditioned floor area of 2,400 square feet. Using Title 24 requirements, what is the maximum allowable air leakage rate at 50 pascals pressure differential?
Correct Answer
C) 6.0 ACH50
Title 24 requires residential buildings to have air leakage not exceeding 6.0 ACH50 (air changes per hour at 50 pascals) for energy efficiency compliance.
Why This Is the Correct Answer
California Title 24 Part 6 (Energy Code) sets a maximum allowable air leakage rate of 6.0 ACH50 (air changes per hour at 50 pascals) for residential buildings. This standard applies regardless of conditioned floor area — it is a performance metric for the building envelope's airtightness. The 2,400 sq ft conditioned floor area detail is included as a distractor; the ACH50 limit is uniform for all residential buildings under Title 24.
Why the Other Options Are Wrong
Option A: 4.8 ACH50
4.8 ACH50 is more stringent than Title 24 requires. While some green building standards (like ENERGY STAR or Passive House) require tighter envelopes, California's Title 24 baseline is 6.0 ACH50. Selecting 4.8 confuses stricter voluntary programs with mandatory code minimums.
Option B: 9.6 ACH50
9.6 ACH50 is double the 4.8 value and exceeds the Title 24 maximum — buildings with this leakage rate would fail the mandatory blower door test. This figure might result from miscalculating based on floor area instead of using the prescribed standard.
Option D: 7.2 ACH50
7.2 ACH50 exceeds the Title 24 maximum of 6.0 ACH50 and would not pass the mandatory blower door test required under the energy compliance pathway. The 7.2 value has no specific code basis and is included as a plausible-sounding distractor.
Memory Technique
Remember '6.0 ACH50' as 'Six at Fifty' — six air changes per hour when pressurized to fifty pascals. The blower door test measures this directly. Think: 'Title 24 gives you SIX chances per hour to exchange air at 50 pascals.'
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