300 Sq Ft Addition Title 24 Requirements
A 300 square foot addition sits in the smallest prescriptive tier, 400 square feet or less. At exactly 300 it is excused from the cool roof requirement, may carry 90 square feet of glazing and does not need quality insulation installation. Duct testing and a certificate of compliance still apply.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
What changes at 300 square feet
Exception 1 to Section 150.2(a) excuses additions of 300 square feet or less from the reflective roof rules of Section 150.1(c)11, which reach steep-sloped roofs in zones 10 to 15 and low-sloped roofs in zones 13 and 15. At 301 square feet the excuse ends. Paperwork has a nearby line: Section 10-103(a)1C lets a department skip or simplify the certificate for additions of less than 300 square feet that need no field verification. Exactly 300 is not less than 300, and extended ducts need verification anyway, so ask which certificate it expects.
Numbers for a 15 by 20 foot room
- Glazing: the cap is the greater of 75 square feet or 30 percent of floor area. Thirty percent of 300 is 90, so the percentage governs above 250 square feet. West-facing glass is held to 60 square feet in zones 2, 4 and 6 to 15.
- Attic: R-38 in zones 1, 2, 4 and 8 to 16, R-30 in zones 3 and 5 to 7, with a radiant barrier in zones 2 to 15.
- Quality insulation installation, which an ECC-Rater verifies, starts above 700 square feet.
A small room still reaches the ducts
Extending any length of existing duct puts the system and the extension under Section 150.2(b)1D: leakage of 10 percent of airflow or less, or 7 percent or less to outside, plus R-6 or R-8 insulation on new ducts in unconditioned space. A ductless mini-split avoids ducts and the capacity caps, but as a new system a heat pump needs refrigerant charge verification. The test is explained under duct leakage testing.
The mistake to avoid
Modeling the addition alone. The manual's example is a 400 square foot room that gets 30 percent glazing when modeled with the existing house but only 20 percent alone. Check a glass-heavy plan both ways; see prescriptive versus performance. The next tier is on the 500 square foot addition page, the roof rule on cool roofing, the general method on room additions, and reports at our residential service.
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. Exception 1 to Section 150.2(a) excuses additions of 300 square feet or less from the roofing requirements of Section 150.1(c)11. At 301 square feet the requirement applies wherever the climate zone calls for it.
Only for additions of less than 300 square feet that need no field verification, and only at its discretion. Even then the work must still meet the code.
Explore Additions and Remodels
- 500 Sq Ft Addition Title 24 Requirements
- 700 Sq Ft Addition Title 24 Requirements
- Addition Over 1,000 Sq Ft: Title 24 Requirements
- Basement Conversion Title 24 Requirements in California
- Does a Basement Conversion Need Title 24?
View all Additions and Remodels guides → · Permits and Compliance · Title 24 guide