Replacing One Window: Does Title 24 Apply?
It depends on what is replaced. A new window is an alteration, so Part 6 applies, but a broken pane, new glass in the existing sash and frame, or the same window reinstalled in the same spot is a repair. A single replacement window may meet U-0.40 and SHGC 0.35 under the 75 square foot exception, except that zone 15 stays at 0.23.
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Repair or alteration
The Commission's manual lists as repairs replacing a broken pane without the whole window, and removing a window for maintenance then reinstalling the same window in the same location. Section 150.2(b)1B adds that glass in an existing sash and frame, or sashes in an existing frame, is a repair if the replacement performs at least as well as the original. Replace the window itself and the work is an alteration.
Moving counts too. The manual treats any envelope component moved to a new location as an alteration, even when the new position overlaps the old one.
What a single new window has to show
- Exception 1 to Section 150.2(b)1B: replacing no more than 75 square feet of vertical glass needs U-0.40 or lower in every zone, and SHGC 0.35 or lower in zones 2, 4 and 6 to 15.
- Zone 15 is stricter: replacement glass is held to SHGC 0.23 under Exception 3.
- Zones 1, 3, 5 and 16 set no SHGC limit for replacement glass.
Without the exception the target would be the zone value in Table 150.1-A, 0.27 or 0.30. Any window, large or small, must also carry its NFRC or default label, leak no more than 0.3 cfm per square foot at 75 pascals if manufactured, and be sealed under Section 110.7. A window removed and reinstalled during an alteration is excepted from the Section 110.6(a) certification rule.
The mistake to avoid
Enlarging the opening. Glass beyond what was removed from that wall is new area, which must meet the new-home U-factor and SHGC, although up to 16 square feet is exempt from the area caps.
Whether the job needs a certificate of compliance is the building department's call: see the window replacement permit question. For several windows, read whole-house replacement and the replacement checklist. Our residential Title 24 reports cover alterations.
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 manual lists replacing a broken pane without the whole window as a repair, and repairs to residential buildings are outside the scope of the Energy Code.
Yes. A manufactured window carries a temporary label with its U-factor, SHGC and visible transmittance, and it stays on until the inspection.
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