Triplex Title 24 Requirements
A triplex built as one apartment-style building is low-rise multifamily under Part 6. That means the LMCC forms, a heat pump in zones 1 to 15 on the prescriptive path, ventilation and air tightness testing in every unit, and solar sized from floor area plus unit count. Three attached townhouse-style units are the exception and follow single-family rules.
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Settle the townhouse question first
Section 100.1 calls a townhouse a single-family dwelling unit in a group of three or more attached units, each running from foundation to roof with open space on at least two sides. Three units that meet that test follow the single-family rules; the single-family manual even lists triplexes beside townhouses. A stacked or corridor-served triplex does not meet it and falls under the multifamily definition. The occupancy group on the permit decides, and the townhome page covers the other side.
What a multifamily triplex carries
- Heating and cooling: Section 170.2(c)3A calls for a heat pump in zones 1 to 15, and an air conditioner with furnace in zone 16, in buildings up to three habitable stories.
- Ventilation: each unit meets Equation 160.2-B, 0.03 times floor area plus 7.5 times (bedrooms plus one), so a 1,000 square foot two-bedroom unit needs 52.5 cfm. Every unit uses the same supply or balanced system type.
- Air tightness: 0.3 cfm at 50 pascals per square foot of unit enclosure, field verified by an ECC-Rater; see compartmentalization.
Solar: the unit count sets a floor
Equation 170.2-C multiplies the unit count by a zone factor between 1.06 and 1.51 kWdc. For three units that term alone runs from 3.18 kWdc in zone 5 to 4.53 in zone 13, and floor area adds to it. A 4,500 square foot triplex in zone 12 computes to 2.76 plus 4.20, or 6.96 kWdc, unless a smaller solar access roof area caps it. The caps and exceptions are on multifamily solar.
Testing three matching units
Sampling is the builder's option. Under Reference Appendix RA2.6 the ECC-Rater tests the first unit of a model in full, then draws one unit at random from the rest, so a triplex still sees at least two units tested. Units with different verified measures go into separate groups.
Paperwork is the LMCC, LMCI and LMCV set explained under LMCC certificate. For the four-unit thresholds see fourplex requirements; the general overview is on triplexes and fourplexes.
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
It depends on the building. Three attached units that each run from foundation to roof with open space on two sides are a townhouse and single-family. A stacked or corridor-served triplex is multifamily.
Not at three habitable stories or fewer. Section 170.2(f) requires solar only; a battery of at least 7.5 kWh is an option that lets the solar size drop by 25 percent.
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View all Multi-Family guides → · Permits and Compliance · Title 24 guide