Do Triplexes and Fourplexes Need Title 24?

The threshold is the unit count, not the size

Three dwelling units is the line. A duplex, whatever its height, is Group R-3 and uses the single-family standards. A triplex built as one apartment-style building is multifamily, and floor area does not change that — one additional unit does.

The exception is the townhouse. Three or more attached units that each run from foundation to roof, with open space on at least two sides, are a townhouse under Section 100.1 of the Energy Code, and a townhouse is a single-family building. So a row of three townhouses uses the single-family standards and the CF1R. See townhome and rowhouse Title 24 reports.

So a triplex and a fourplex are assessed under the multifamily subchapters and produce the low-rise multifamily form family: a Certificate of Compliance at design stage, a Certificate of Installation during construction, and a Certificate of Verification where field testing is required.

Almost always low-rise

Triplexes and fourplexes are rarely more than three habitable storeys, which keeps them on the low-rise multifamily side and out of the nonresidential form set that applies from four storeys up. Worth checking on a tall, narrow urban infill design, because the test is habitable storeys and a mostly-above-grade lower level can count.

Solar on new construction

A newly constructed low-rise multifamily building carries a photovoltaic requirement. It applies to new fourplexes and triplexes as it does to a larger low-rise block, subject to a short list of exceptions that have to be established for the specific building. A project converting or altering an existing building is a different case and is not new construction.

Why the distinction is worth settling early

Because a designer who has done duplexes and assumes the same route for a fourplex is working to the wrong standards, on the wrong forms, from the first sketch. It is a cheap thing to confirm at concept stage and an expensive one to discover at plan check.

Common Title 24 Questions

1. Do apartments need Title 24?
2. Does a duplex need Title 24?
3. Which Title 24 forms does a multi-family project use?
4. What is an LMCC certificate?
5. How much does a multi-family Title 24 report cost?
6. How long does a multi-family Title 24 report take?

Explore Multi-Family

1. Triplex Title 24 Requirements
2. Townhome and Rowhouse Title 24 Report
3. Adaptive Reuse and Title 24
4. Title 24 for an ADU on a Multifamily Property
5. Do Apartments Need Title 24?

View all Multi-Family guides → · Permits and Compliance · Title 24 guide