A House With a Shop, Office or Studio: Does Title 24 Need Two Reports?
It depends on the split of conditioned floor area. If one use is under 20 percent, the whole building may follow the larger use for envelope, HVAC and water heating. If neither is under 20 percent, two compliance submittals are needed, one per occupancy. Lighting and mandatory measures are checked for each use either way.
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Do the area arithmetic first
When a building houses residential and nonresidential occupancies, each space must meet the Part 6 provisions for its own occupancy (Section 100.0(f)). Two shortcuts follow, based on floor-area percentages.
Under 20 percent: the minor occupancy
If one occupancy is at least 80 percent of the conditioned floor area, the entire envelope, HVAC and water heating may be designed to that occupancy's provisions (Exception 1 to Section 100.0(f)). The compliance manual calls the smaller use a minor occupancy when it is less than 20 percent. Lighting and the mandatory measures still apply to each space under its own occupancy. At exactly 80 percent the two texts word the boundary differently ("at least 80" against "less than 20"), so confirm that case with the department.
Neither under 20 percent: two submittals
The manual says the occupancies are then considered separately, with two compliance submittals, each using the calculations and forms of its own standards.
The lighting test is separate
If one occupancy is at least 90 percent of the combined conditioned and unconditioned area, indoor lighting may follow that occupancy alone (Exception 2).
A worked example
A 2,400 square foot conditioned house with a conditioned 400 square foot shop in the same building totals 2,800, so the shop is about 14 percent. It is a minor occupancy, so the building can be designed as a house for envelope, HVAC and water heating, with the shop's lighting checked separately. With a 700 square foot shop instead, the shop is about 23 percent, so neither use is minor and two submittals follow.
Apartments over shops
For multifamily buildings, including mixed use, the performance certificate is the LMCC-PRF-01-E at three or fewer habitable stories and the NRCC-PRF-01-E at four or more (multifamily manual, Section 170.1). A habitable story has at least 50 percent of its volume above grade, and mezzanines do not count.
See residential versus nonresidential, apartment Title 24 and a detached office or studio, which is its own building. A commercial or residential report starts once the areas are known.
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
The building department assigns occupancy groups under the building code. Ask it before you size the report.
No. A separate building is judged on its own. These tests apply to occupancies sharing one building.
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View all Who Needs Title 24? guides → · Title 24 Guide · Title 24 guide