When Does Roof Replacement Trigger Insulation Upgrades?
Usually not. A steep-sloped re-roof over a vented attic carries no insulation rule of its own. Insulation is triggered by a low-sloped roof (R-14 in most zones), by opening the space between rafters (R-19 minimum), or by altering the ceiling under a vented attic or installing new ducts in it, which brings R-49 in most zones.
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Four roof jobs, four outcomes
Shingles on a steep roof over a vented attic
Section 150.2(b)1Ii asks for a cool roof product or one of its listed equivalents, and nothing about insulation. Stripping the surface does not touch the ceiling, so the attic rules stay out of it.
A low-sloped roof
When more than 50 percent is replaced, Table 150.2-F calls for R-14 continuous insulation, or an assembly U-factor of 0.039, in zones 1, 2, 4 and 8 to 16. Zones 3 and 5 to 7 have no requirement. Existing R-10 continuous insulation above or below the deck excuses the work. So does an existing U-0.056, or R-19 between rafters against the deck, in zones 1, 2, 4 and 8 to 10. Where rooftop equipment or a parapet would leave too little flashing height, the figure can drop to R-4.
A rafter roof with the sheathing off
The compliance manual treats the roof as altered once the space between framing members is accessible. An altered rafter roof must reach R-19, or U-0.054, under the exception to Section 150.0(a)2. The manual's section on replacing roof sheathing is left to the 2022 manual, so a deck replacement is worth confirming with the department.
New ducts or ceiling work under a vented attic
Section 150.2(b)1J applies when the ceiling is altered, which includes adding or replacing attic insulation, or when an entirely new duct system goes in the attic. It asks for R-49 or U-0.020 in zones 1 to 4, 6 and 8 to 16. Existing R-38 excuses all of it. The detail is on attic insulation for remodels.
The mistake to avoid
Swapping wood shakes for asphalt shingles is a replacement, not a repair, so the roofing rule still applies. The cool roof side is on cool roof requirements for a re-roof, the general rules on insulation requirements, and the full re-roof overview on re-roofing. Start an order from residential Title 24 reports.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
Not by itself on a steep roof over a vented attic. Insulation attaches to low-sloped roofs, altered rafter roofs and altered vented-attic ceilings, and the building department decides how it treats a deck repair.
No. The manual says an ECC-Rater is not required for the vented-attic requirements, and the building department verifies them.
Explore Roofs
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- Do I Need Title 24 for a Roof Replacement?
- Cool Roof Requirements When Reroofing a House
- Are Your Shingles Title 24 Compliant?
- Remodel With Roof and Attic Insulation Changes: Title 24 Checklist
View all Roofs guides → · Windows and Building Envelope · Title 24 guide