Which Wall Assembly Meets Title 24?
A new home on the prescriptive path needs framed walls at U-0.048, or U-0.065 in climate zones 6 and 7. Cavity batts alone fall short: R-15 in a 2x4 wall gives 0.095 and R-21 in a 2x6 wall gives 0.069. Continuous insulation closes the gap, for example R-5 on a 2x6 wall or R-10 on a 2x4 wall.
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Two limits for one wall
Section 150.0(c) sets the floor for every wall: U-0.095 for 2x4 framing and U-0.069 for 2x6, met by R-15 and R-21 batts at 16 inches on center. Table 150.1-A sets the higher bar for a new home. Both figures describe the whole assembly, framing included, so a batt's R-value alone does not give the result.
Reaching 0.048
Joint Appendix Table 4.3.1 lists wood-framed walls at 16 inches on center with half-inch gypsum board.
- 2x6 with R-21: R-5 continuous gives 0.048. R-4 gives 0.051 and fails.
- 2x6 with R-19: R-7 gives 0.046. R-6 gives 0.049 and fails.
- 2x4 with R-15: R-10 gives 0.045. R-8 gives 0.050 and fails.
- 2x4 with R-13: R-10 gives 0.047.
Zones 6 and 7
The limit is 0.065. A 2x4 wall with R-15 passes with R-4 continuous, at exactly 0.065. A 2x6 wall with R-21 misses at 0.069 but passes with R-2, at 0.059.
Using the table
Continuous insulation may go inside the studs, outside them or both. By hand, its rated R-value must equal or exceed the column used, with no interpolation; approved software can calculate other thicknesses. The R-15 and R-21 rows call for higher-density batts.
When you are not building new
An addition that extends an existing wall may keep its framing depth with R-15 or R-21 cavity insulation, as room additions explains. A wall that cannot reach the figure can be traded off under the performance approach. The rest of the envelope is on insulation requirements, with quality insulation installation covering the installation check.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
Not for a new home on the prescriptive path. R-21 batts reach 0.069 against a limit of 0.048, and R-5 continuous insulation brings the wall to 0.048. R-21 is the mandatory floor.
No. Joint Appendix Table 4.3.1 allows it on the inside, the outside or both.
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