Under California's Title 24 energy efficiency standards, what is the maximum thermal bridging factor allowed for wood-framed walls when calculating U-factors for compliance?
Correct Answer
B) 0.85
Title 24, Part 6, Section 110.8 specifies that wood-framed walls must use a thermal bridging factor of 0.85 maximum when calculating assembly U-factors. This factor accounts for thermal bridging through framing members and is critical for demonstrating energy code compliance in California's climate zones.
Why This Is the Correct Answer
Title 24, Part 6, Section 110.8 specifies a thermal bridging factor of 0.85 for wood-framed walls when calculating assembly U-factors. This factor accounts for the reduced insulating performance caused by heat conduction through wood framing members (studs, plates, headers) that 'bridge' the insulation layer. Using 0.85 ensures the compliance calculation accurately reflects real-world wall performance.
Why the Other Options Are Wrong
Option A: 0.80
A factor of 0.80 would represent greater thermal bridging degradation than Title 24 specifies for wood framing. Using 0.80 would understate the wall's thermal performance and is not the value prescribed in Section 110.8.
Option C: 0.75
A factor of 0.75 would indicate even more severe thermal bridging than wood framing actually produces. Title 24 does not use 0.75 for standard wood frame construction — this value would result in an overly conservative (and inaccurate) compliance calculation.
Option D: 0.90
A factor of 0.90 would underestimate the thermal bridging effect of wood framing, overstating the wall's insulating performance. Title 24 sets the maximum at 0.85 — using 0.90 would produce an optimistic U-factor that may not reflect actual energy performance.
Memory Technique
Remember '0.85 = 85% efficient for wood framing.' Wood studs bridge 15% of the wall area (approximately), reducing the assembly's insulating effectiveness by about 15%. So the thermal bridging factor is 0.85 — 85% of the insulation value survives thermal bridging through the wood.
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