Skylight Shaft Insulation: What Title 24 Expects Around the Light Well
Yes, where the shaft separates conditioned space from the attic. Under Quality Insulation Installation the shaft framing is insulated to at least the wall R-value on the Certificate of Compliance, with an air barrier on the attic side and the room side touching the drywall. For a remodel the Standards are silent, so the building department decides.
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What the shaft is in code terms
Section 100.1 defines a skylight as fenestration installed on a roof less than 60 degrees from the horizontal, and skylight area as the rough opening. The shaft is the framed passage from that opening down to the ceiling. Where it crosses an attic, its walls divide a heated room from unconditioned space, so Reference Residential Appendix RA3.5 treats it beside the kneewall rule.
What the ECC-Rater checks in a batt-insulated shaft
- Insulation meets or exceeds the wall R-value on the Certificate of Compliance, with no gaps or compression.
- Air-permeable insulation facing the attic has its backside covered by a continuous air barrier.
- The room side of the insulation touches the drywall or other finish.
- Friction fit, stapled flanges or netting hold it up.
- Framing encloses it on all sides, with plates at top and bottom.
Steel studs and spray foam
A steel-framed shaft needs continuous insulation over the outside faces of the studs, unless the report uses the steel-stud U-factors in Joint Appendix JA4 Table 4.3.4. Sprayed foam goes in without gaps, fully adhered and self-supporting. Closed-cell foam need not fill the cavity if its thickness matches the compliance documents and the plates and framing ends are sprayed full.
When this applies
QII is prescriptive for new homes in all 16 climate zones and for additions over 700 square feet, as the QII overview explains. A performance model can trade it away at a modeling penalty. The installer signs a Certificate of Installation, and an ECC-Rater, the title that replaced HERS rater on 1 January 2026, verifies the work before the permit is finalized.
A skylight added in a remodel
The alteration section holds a new skylight to the area, U-factor and SHGC limits of Section 150.2(b)1A, lists no QII item and never mentions shaft framing. Ask the department what it wants, and draw the shaft in section with the insulation called out. Glass numbers are on the skylight requirements and skylight replacement pages. See our residential 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
The protocol covers shaft framing that separates conditioned from unconditioned space. A shaft that passes only through heated space is not the target of that rule.
The insulation installer signs the Certificate of Installation, and the ECC-Rater verifies thickness and installation before the permit is finalized.
Explore Skylights
- Solar Tubes (Tubular Daylighting Devices): Title 24 Rules
- Title 24 Skylight Requirements for Homes
- How Many Square Feet of Skylight Can I Add Under Title 24?
- Skylight Replacement: Title 24 Requirements
View all Skylights guides → · Windows and Building Envelope · Title 24 guide