Do I Need Title 24 for a Room Addition?
Yes. A room that adds conditioned floor area and volume is an addition under Section 150.2(a), and the definition sets no minimum size. The report turns on the route: model the addition alone, model the existing house with the addition, or treat the whole house as new construction.
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What counts as an addition
Section 100.1 defines an addition as any change that increases both conditioned floor area and conditioned volume. The compliance manual's examples include enclosing a patio, legalizing a room built without a permit and a floor-to-ceiling bay window. Separate additions under one permit are added together to set the size tier.
Three routes, three trade-offs
- Addition alone. Only the new room is modelled, so the old house supplies just its floor area and bedroom count. Upgrades elsewhere cannot offset the room, and some allowances fall away: in the manual's example a 400 square foot addition is held to 30 percent glazing with the existing house (zones 2, 4 and 6 to 15) but 20 percent alone (Table 150.1-A).
- Existing house plus addition. The whole house is modelled and unaltered parts stay as they are. This allows the most trading but needs plans of the old building.
- Whole house as new construction. For extensive changes, since every existing feature must reach current code.
What the room does to the rest of the house
Extending existing ducts by any length puts the old duct system and the extension through a sealing test: leakage of 10 percent of airflow or less, or 7 percent or less to outside, or every accessible leak sealed and smoke-tested by an ECC-Rater. The old equipment need not comply, but its heating capacity must meet CRC 303.10 (load calculations).
Whole-dwelling mechanical ventilation is excused for an addition of 1,000 square feet or less that is not a new dwelling unit; above that, the airflow is figured on the existing floor area plus the addition (whole-house ventilation). New kitchen and bathroom exhaust still applies, and solar PV does not.
Paperwork and next step
Prescriptive additions use CF1R-ADD-01-E (under 1,000 square feet), CF1R-ADD-02-E without field verification, or CF1R-NCB-01-E at 1,000 square feet or more; a modelled route produces a CF1R-PRF-01-E. Where an ECC-Rater must verify an item, the certificate is registered with an ECC-Provider first. Size tiers and glazing caps are on room additions; see also sunrooms, second stories and garage conversions.
Common Title 24 Questions
- What is Title 24?
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- How much does a Title 24 report cost?
- How long does a Title 24 report take?
- What is included in a Title 24 report?
- What plans do I need to upload?
Frequently Asked Questions
The definition of an addition sets no minimum size: any change that increases conditioned floor area and volume qualifies. Whether a permit is needed at all is the building department's decision.
Not on the addition-alone or existing-plus-addition routes. Upgrades elsewhere are optional trade-offs, apart from the duct testing that extending existing ducts triggers.
Explore Additions and Remodels
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View all Additions and Remodels guides → · Permits and Compliance · Title 24 guide