Attic Conversion to Living Space: Title 24 Requirements
An attic conversion is an addition, and roof insulation is only half the job. The other half is mechanical: ducts or an air handler left in the attic, the unused attic behind the knee walls, the radiant barrier and the access hatch each carry their own rule. Plan the equipment before the insulation.
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Where the ducts end up sets the package
Above 700 square feet the manual offers two roof-and-ceiling options (Tables 9-1 and 9-2). Option B keeps the duct system and air handler in the attic. Option C requires them to be in conditioned space and in return asks for no roof deck insulation. At 700 square feet or less the choice does not arise: a ventilated attic takes R-38 or R-30 by zone with a radiant barrier in zones 2 to 15, and an enclosed rafter ceiling follows Section 150.0.
Ducts that stay in unconditioned attic
New or extended ducts there take R-8 in zones 1, 2, 4 and 8 to 16 and R-6 in zones 3 and 5 to 7 (Table 150.2-D). Extending an existing system, by any length, brings the combined duct system under the leakage test: 10 percent of airflow or less, or 7 percent or less to outside. The existing equipment need not meet current efficiency rules, but its heating capacity must satisfy CRC 303.10. A ductless unit avoids all this.
The attic left behind the knee walls
The manual separates two cases. If the attic is an open, undivided space, the entire roof or ceiling is insulated, including portions over unconditioned space such as a garage. If a continuous air barrier divides the attic over the new room from the rest, only the part over conditioned space is insulated, and the manual recommends insulating the barrier too. Doors or hatches into the leftover attic need permanently attached insulation and a gasket (Section 150.0(a)3).
Radiant barrier placement
The manual says a required radiant barrier goes on the underside of the attic roof assembly and the gable wall ends that belong to the addition, nowhere else. Table 9-1 notes it does not apply to cathedral ceilings. The roof-line and knee-wall values are on attic conversion.
For floor and duct questions over a garage see bonus rooms over a garage. Duct values are on duct insulation, and the cellar case is basement conversion. Our residential reports start from your plans.
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
Yes. For additions over 700 square feet the manual's Option B is written around ducts and air handler staying in the attic, and Option C is the alternative that moves them into conditioned space.
No. Where one is required, it goes on the underside of the attic roof assembly and gable ends associated with the addition, and not on cathedral ceilings.
Explore Insulation
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- Cathedral Ceiling Insulation Under the 2025 Energy Code
View all Insulation guides → · Windows and Building Envelope · Title 24 guide