Second-Story Addition Title 24 Requirements

A second story is an addition under §150.2(a), on the same 700 square foot line as any other, but its new roof and attic bring ceiling, roof-deck and cool roof rules of their own. A full second floor can also pass 1,000 square feet, where whole-house ventilation and, in zones 8 to 14, a whole-house fan come in.

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Same addition rules, different building parts

Adding a story increases conditioned floor area and volume, so it is an addition. The prescriptive tests split at 700 square feet and again at 400 exactly as they do for a ground-floor room, and so do the glazing caps. Those are set out on does a room addition need Title 24 and not repeated here. This page is about what building upwards adds.

The old roof stops counting

Once the new floor is built, the old first-floor ceiling sits between two conditioned floors. Section 150.0(a) applies to ceilings and rafter roofs that separate conditioned space from unconditioned space or outdoors, which that ceiling no longer does. What has to meet the roof and ceiling rules is the new roof over the new story.

The new roof and attic

  • Ceiling insulation. For an addition of 700 square feet or less, a ventilated attic needs R-38 in zones 1, 2, 4 and 8 to 16 and R-30 in zones 3 and 5 to 7, with a radiant barrier in zones 2 to 15. Larger additions take the attic options of Table 150.1-A.
  • Roof-deck insulation. Section 150.2(a) applies §150.0(a) to additions, and §150.0(a)1 requires the roof deck of a newly constructed attic above conditioned space to reach U-0.184 in zones 4 and 8 to 16, which the compliance manual equates to about R-3 or R-4. It does not apply if the air handler and ducts are entirely in conditioned space, if no more than 12 feet of supply duct is outside it, or if the system is ductless.
  • Cool roof. Additions over 300 square feet meet the roofing rules of §150.1(c)11: steep-sloped roofs in zones 10 to 15 and low-sloped roofs in zones 13 and 15.

Heating and cooling the new floor

Whether the existing system can serve the new floor is a sizing question. If it is extended, Exception 3 to §150.2(a) spares the existing equipment from Part 6, provided its heating capacity still meets CRC 303.10. Extending any length of duct brings the existing duct system and the extension under the sealing rules of §150.2(b)1D. A new system serving the addition meets the mandatory equipment rules in full. Either way the sizing comes from a load calculation that, for an addition, may not assume more air leakage than Table 150.2-C allows; see Title 24 HVAC load calculations.

The 1,000 square foot line

A full second floor can exceed 1,000 square feet, where two more requirements begin:

  • Whole-dwelling mechanical ventilation applies, with the airflow based on the entire dwelling, existing floor area plus the addition (§150.2(a)1Ci).
  • The ventilation cooling requirement of §150.1(c)12 applies, which Table 150.1-A sets as a whole-house fan in zones 8 to 14, chosen from the Home Ventilating Institute directory.

At 1,000 square feet or less both are excused, under §150.2(a)1Ci and Exception 5 to §150.2(a). Ventilation detail is on whole house ventilation.

Trading with the house below

Exception 6 to §150.2(a) means a second story brings no solar PV requirement. If the existing house is being improved at the same time, the performance path can model the existing, altered and added parts together under §150.2(a)2B, so upgrades downstairs can offset a shortfall upstairs.

Common Title 24 Questions

  1. When is Title 24 required for a home?
  2. Does a remodel need Title 24?
  3. Does a room addition need Title 24?
  4. What plans are needed for a residential Title 24 report?
  5. How much does a residential Title 24 report cost?
  6. How long does a residential Title 24 report take?

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