ADU Window SHGC Requirements
A new ADU may not exceed an SHGC of 0.23 in climate zones 2, 4 and 6 to 14, or 0.20 in zone 15. Zones 1, 3, 5 and 16 have no prescriptive SHGC limit. Where a limit applies, west-facing glass is capped at 5 percent of floor area, and exterior shading can stand in for a lower-SHGC product.
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The zone sets
- 0.23: zones 2, 4 and 6 to 14
- 0.20: zone 15 only
- No limit: zones 1, 3, 5 and 16
Zone 15 relaxes for an existing building: windows added or replaced there as an alteration are held to 0.23, not 0.20.
West-facing glass is the second test
In zones 2, 4 and 6 to 15 west-facing fenestration is capped at 5 percent of floor area; zones 1, 3, 5 and 16 have no cap. West-facing means within 45 degrees of true west, which takes in northwest walls and leaves out southwest ones. On a 600 square foot ADU that is 30 square feet. An addition of 700 square feet or less is held to a flat 60 square feet instead, and a skylight pitched below 1:12 counts as west-facing in any direction.
Shading and averaging
Section 150.1(c)4 lets exterior shading do the work where a limit applies: an operable exterior louver or other exterior device that achieves the required SHGC, or on south-facing glass an overhang that fully shades it at solar noon on 21 August and leaves it substantially in sun on 21 December. Insect screens and interior blinds do not count. Windows and glazed doors are otherwise area-weighted, so a 0.20 unit offsets a 0.26 unit of equal area.
Where defaults fail
The lowest SHGC in the default table for any double-pane product is 0.53, so only an NFRC 200 rating gets a window under 0.23. In the performance method the manual also warns that an SHGC of 0.35 or lower can raise heating loads against the standard design in zones 1, 3, 5 and 16.
The U-factor side is on the ADU window U-factor page, general window rules on windows and Title 24, and skylights, which carry their own 0.30, on the skylight page. Find your zone on the climate zones page, then start from the ADU reports page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
A new ADU takes 0.20. Windows added or replaced in an existing building in zone 15 take 0.23, and skylights up to 16 square feet per dwelling unit may use 0.30.
Not prescriptively. Zones 1, 3, 5 and 16 have no SHGC limit and no west-facing cap, though the U-factor and total glass area limits still apply.
Explore ADU and JADU
- ADU Window U-Factor Requirements
- Attached ADU Title 24 Checklist
- California ADU Rules and Title 24
- Can a New ADU Use a Gas Furnace?
- Can a New ADU Use a Gas Water Heater?
View all ADU and JADU guides → · Permits and Compliance · Title 24 guide