Addition Over 1,000 Sq Ft: Title 24 Requirements
An addition that adds more than 1,000 square feet must have whole-dwelling mechanical ventilation sized on the entire dwelling, existing floor area plus the addition, not on the new rooms alone. Zones 8 to 14 also need a whole-house fan on the prescriptive path. Neither applies at 1,000 square feet or less.
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The airflow is sized on the whole house
Section 150.2(a)1C requires the airflow of Section 150.0(o)1C, with the floor area taken as the existing dwelling plus the addition. Equation 150.0-B gives total cfm as 0.03 times floor area plus 7.5 times the number of bedrooms plus one. Take a 1,800 square foot, three-bedroom house with a 1,100 square foot addition that makes four bedrooms: 0.03 times 2,900 is 87, and 7.5 times 5 is 37.5, so 124.5 cfm before the infiltration credit. The same house with a 1,000 square foot addition needs none of this.
What the field check involves
- An ECC-Rater confirms airflow with a flow hood or flow grid under Reference Residential Appendix RA3.7.
- Fans are rated at 1.0 sone or less, and the on-off switch carries the label Section 150.0(o)1J prescribes.
- The system may be exhaust, supply, balanced or central-fan integrated, and verified envelope leakage below the 2 ACH50 default lowers the fan size.
The whole-house fan
In zones 8 to 14, Table 150.1-A requires a whole-house fan on the prescriptive path. It must be HVI listed, with at least 1.5 cfm per square foot of conditioned floor area and 1 square foot of attic vent for each 750 cfm unless it vents directly outdoors. The homeowner receives a one-page operating sheet.
What still does not apply
Solar PV is not required for an addition of any size, under Exception 6 to Section 150.2(a). A new 1,100 square foot house in zone 12 would be assessed 2.07 kW (1,100 times 0.613 divided by 1,000, plus 1.40). The prescriptive certificate is CF1R-NCB-01-E, and performance uses CF1R-PRF-01-E.
The exact line is discussed on the 1,000 square foot addition page. For sizing see whole-house ventilation and IAQ fans; for the fan see whole-house fans, and for solar see residential solar requirements. Our residential reports cover the whole package.
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
No. For an addition over 1,000 square feet the airflow uses the whole dwelling unit, the existing conditioned floor area plus the addition. A new dwelling unit is sized on its own area.
No. Exception 6 to Section 150.2(a) says photovoltaic systems are not required for additions, whatever their size.
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