Is a townhouse single-family or multifamily under Title 24?

Single-family. Section 100.1 lists a townhouse as a single-family building, and the Energy Commission’s multifamily manual says all townhouses follow the single-family requirements regardless of the number of habitable stories.

Which forms does a townhouse project use?

The single-family set: a CF1R Certificate of Compliance (CF1R-PRF-01-E or CF1R-NCB-01-E), CF2R certificates of installation and CF3R certificates of verification. Not the LMCC or NRCC forms.

Are townhomes stacked over flats still townhouses?

Not under the definition, which requires each unit to extend from foundation to roof. How the building is assessed then depends on its occupancy classification, which the building department sets.

Do townhouses need the multifamily compartmentalization test?

No. Section 160.2, where that test sits, states that it does not apply to townhouses or to dwellings containing two dwelling units.

Townhome and Rowhouse Title 24 Report

Under the Energy Code a townhouse is a single-family building, not a multifamily one: §100.1 defines it as a single-family dwelling unit in a group of three or more attached units, each extending from foundation to roof with open space on at least two sides. It is documented on the single-family CF1R forms, not the multifamily LMCC or NRCC set.

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Two definitions decide it

Section 100.1 lists what counts as a single-family building: a Group R-3 building with two or fewer dwelling units, a townhouse, and a few other R-3 and Group U cases. A multifamily building is a Group R-2 building other than a hotel, motel or timeshare, a Group R-4 building, or certain R-3 congregate residences. A townhouse is in the first list by name.

The Energy Commission’s multifamily compliance manual says the same thing plainly: single-family homes, duplexes and all townhouses, regardless of the number of habitable stories, follow the single-family requirements. A row of homes sits with the multi-family projects on this site because it is attached housing. The report it needs is a single-family one.

Townhome, rowhouse or stacked flats

Neither "townhome" nor "rowhouse" is a term the code uses. What matters is the shape of each unit:

Side by side, three or more in a row, each running from foundation to roof with open space on at least two sides: a townhouse, so single-family.
Two attached units: a Group R-3 building with two dwelling units, also single-family, covered on does a duplex need Title 24.
Units stacked over one another, such as flats, or a townhome above a flat: no unit runs from foundation to roof, so the building is not a group of townhouses. Where the building department classifies it as Group R-2, it follows the multifamily standards, as on triplex and fourplex Title 24.

Height carries one caveat. The single-family manual’s own example says a four-story townhouse follows the single-family standards if the building department classifies it as Group R-3, but the multifamily standards if it is classified R-2 and all four stories are habitable. Confirm the occupancy classification before the design is fixed.

Which forms

A townhouse uses the single-family Certificate of Compliance: CF1R-PRF-01-E on the performance path or CF1R-NCB-01-E on the prescriptive path, followed by CF2R certificates of installation and CF3R certificates of verification from the ECC-Rater. It does not use the LMCC forms of low-rise multifamily, nor the NRCC forms used from four habitable stories up; those are explained on multi-family Title 24 forms. The requirements themselves are those of a new single-family home, set out on the new home Title 24 report page.

What changes because the homes are attached

A few single-family rules are written with attached units in mind:

Ventilation. Under §150.0(o)1C, an attached unit that shares no floor or ceiling with another dwelling may reduce its required mechanical ventilation. Equation 150.0-F applies a factor, Aext, equal to the share of the unit’s envelope surface that is not attached to garages or other dwelling units. An end unit has more exterior envelope than a middle one, so the two can need different fan airflows. Vertically attached units may not take the reduction.
No compartmentalization test. Section 160.2, which holds the multifamily air-leakage test between units, states that it does not apply to townhouses or to dwellings containing two dwelling units.
Duct leakage. Section 150.0(m)11 names single-family dwellings and townhouses together: total leakage of 5 per cent of air handler airflow or less.
Solar. Section 150.1(c)14 applies to all single-family residential buildings, and Equation 150.1-C carries a term for the number of dwelling units, so a row is sized on its unit count as well as its floor area. See solar on a new home.

What the report needs

Plans for each unit type, with the walls each unit shares with its neighbours marked separately from its exterior walls, windows and roof. A site plan showing which way each unit faces matters more than on a detached house, because the same plan facing a different direction performs differently, and an end unit differs from a middle one. Equipment schedules and bedroom counts complete the set.