Do I Need Title 24 for a Tiny Home in California?
It depends on what the tiny home legally is. On a chassis it may qualify as a recreational vehicle or park trailer, built to RV standards outside the Energy Code. On a foundation it is a dwelling and the 2025 code applies in full, with solar the rule that varies most by climate zone at 400 square feet or less.
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Three questions first
Is it on wheels? Then see the RV and park trailer distinctions on tiny homes and Title 24; HCD says a mobile unit that fits no such category is a dwelling under the Building Standards Code. Is it on a foundation and built on site? Then it is a dwelling, and HCD's ADU Handbook says it is subject to ADU law if it meets the Government Code definition of an ADU. Is the lot in a mobilehome park or special occupancy park? The handbook says such a lot allows only one manufactured home, mobilehome or recreational vehicle, so ADU law does not allow an ADU there.
Solar on a foundation tiny home
A tiny home is a dwelling unit, so Equation 150.1-C adds the dwelling-unit factor to the floor-area term. For the 80 to 400 square feet HCD's bulletin describes, the result stays under the 1.8 kWdc line almost everywhere. At 300 square feet only zone 15 reaches it (1.94 kW); at 400 square feet zones 13 and 15 do (1.87 and 2.09 kW). Everywhere else no PV is required, and a roof with little solar access can lower the figure further. Check your zone on the climate zone pages.
What small size buys
Units of 500 square feet or less may use an electric water heater with point-of-use distribution, and units with one bedroom or less a 120-volt heat pump water heater. There is no whole-house fan requirement. These are listed with sources on the live tiny home page, and detached ADUs covers the new-building route.
The mistake to avoid
Buying a unit sold as a tiny home without asking which legal category it was built under. HCD describes park trailers, often sold as tiny homes, as a type of RV meant for recreational or seasonal use. Factory-built units carry an HCD insignia (prefab homes), and a container build is on container homes. Our ADU reports and residential reports both start from your plans.
Common Title 24 Questions
- What is Title 24?
- Do I need a Title 24 report?
- 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
Not if it is a recreational vehicle or park trailer, which HCD says is built to RV standards, not the Building Standards Code. A mobile unit that fits no such category is a dwelling.
Often not. At 300 square feet only climate zone 15 reaches the 1.8 kWdc line, and at 400 square feet zones 13 and 15. The department confirms your calculation.
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View all Building Permit Questions guides → · Permits and Compliance · Title 24 guide