Raised Floor Insulation Requirements Under Title 24

Why R-19 and not R-13

Section 150.0(d) caps a raised floor at U-0.037 and says a wood-framed floor may show it with R-19 or more. Table 150.1-A repeats the figure for every zone. In JA4 Table 4.4.1, a 2x6 floor over a vented crawl space at 16 inches on center reaches 0.037 with R-19, while R-13 reads 0.046 and R-11 reads 0.049. For a floor open to outdoor air with no crawl space, Table 4.4.2 lists R-19 at 0.049, and it takes R-6 of added continuous insulation to read 0.037, though the R-19 route in Section 150.0(d) still applies.

Holding the batts up

The tabulated U-factors are valid only if the insulation is supported so it cannot fall or sag. The manual describes hangers, which are heavy wires up to 48 inches long placed 18 inches or less apart before the batts are rolled out, or netting stapled under the joists. Cavity insulation should touch the subfloor, with no air space against it, and should not cover foundation vents.

Concrete raised floors

A concrete floor over unconditioned space follows Table 3-8 of the manual, which matches Table 150.1-A.

• Zones 1, 2, 11, 13, 14 and 16: U-0.092 or less, meaning R-8 continuous insulation.
• Zones 12 and 15: U-0.138 or less, meaning R-4.
• Zones 3 to 10: no requirement.

Additions and altered floors

An addition takes R-19 or U-0.037 in every size band (Table 9-4). When an existing floor is altered, it must meet Section 150.0(d). Under the performance method, credit for the new insulation is measured against the Table 150.2-G baseline, and only an ECC-Rater verification of the existing R-value changes it.

One exception worth knowing

A controlled-ventilation or unvented crawl space may omit floor insulation, if its four conditions are met, as set out on crawl space insulation. A garage below a living space is on floor insulation over a garage. Slab floors are on slab floors for additions, and the installation check on quality insulation installation. Order from residential Title 24 reports.

Common Title 24 Questions

1. When is Title 24 required for a home?
2. Does a remodel need Title 24?
3. Does a room addition need Title 24?
4. What plans are needed for a residential Title 24 report?
5. How much does a residential Title 24 report cost?
6. How long does a residential Title 24 report take?

Frequently Asked Questions

Is R-19 enough in a 2x8 floor?

Does an altered floor have to reach R-19?

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