Multifamily Addition Title 24 Requirements
An addition to an existing multifamily building follows Section 180.1. The addition itself meets prescriptive envelope and lighting rules that change at 300 and 700 square feet, existing HVAC that is only extended need not be upgraded, and no solar panels or batteries are required. A new dwelling unit is ventilated by its own floor area.
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What counts as an addition
Added conditioned floor area and volume is an addition, and so is space that becomes conditioned for the first time. Section 180.1 gives two routes: the prescriptive tiers of 180.1(a), or a performance model of the addition alone, or of the existing building plus alteration plus addition, under 180.1(b).
Three size breaks
- Over 700 square feet: Section 170.2(a) applies with edits. Extended wood walls keep their dimensions with R-15 in 2x4 framing or R-21 in 2x6, and glazing is capped at the greater of 175 square feet or 20 percent of the addition's floor area.
- 700 square feet or less: a ventilated attic needs U-0.025 (R-38) in zones 1, 2, 4 and 8 to 16, or U-0.031 (R-30) in zones 3 and 5 to 7, and windows follow Table 180.2-B. Quality insulation installation does not apply.
- 300 square feet or less: the roofing product reflectance rule of Section 170.2(a)1A is excused.
What an addition does not drag in
- Existing heating or cooling that is extended into the addition need not comply, although extended ducts must meet Sections 180.2(b)2Ai and 2Aii.
- Solar panels and batteries are not required, and solar-ready provisions are skipped when the roof area grows by 2,000 square feet or less.
- Whole-dwelling ventilation airflow is not required when an addition adds 1,000 square feet or less to an existing unit. Above that the rate uses the whole unit's floor area, and no unit air leakage test applies.
New water-heating equipment serving a dwelling unit meets Section 170.2(d). Forms are the LMCC set up to three habitable stories and the nonresidential set above, explained under LMCC certificate. The mistake to avoid is bundling the addition with work inside existing units: altered components go through Section 180.2, covered on apartment unit remodels. New units on a multifamily lot are discussed under ADUs on multifamily property, the building basics under apartments, and reports at the multi-family service.
Common Title 24 Questions
- Do apartments need Title 24?
- Does a duplex need Title 24?
- Do triplexes and fourplexes need Title 24?
- Which Title 24 forms does a multi-family project use?
- What is an LMCC certificate?
- How much does a multi-family Title 24 report cost?
Frequently Asked Questions
No. Exception 6 to Section 180.1 says photovoltaic and battery systems under Sections 170.2(f) to (h) are not required for additions.
An addition of 300 square feet or less is excused from the roofing product requirement of Section 170.2(a)1A. Above 300 square feet it applies where the zone calls for it.
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View all Multi-Family guides → · Permits and Compliance · Title 24 guide