Title 24 for a Remodel With Existing Single-Pane Windows
Replacing single-pane windows is an alteration, so the new windows must meet the replacement limits in Section 150.2(b)1B. If they cannot, the performance method can trade the shortfall, and an ECC-Rater can verify the old windows first so the upgrade is credited against what was really there.
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Two ways to show it
On the prescriptive path, replacement windows meet the Table 150.1-A values: a U-factor of 0.30 in zones 6 to 10 and 15 or 0.27 in zones 1 to 5, 11 to 14 and 16, plus an SHGC of 0.23 in zones 2, 4 and 6 to 15. On the performance path, Table 150.2-G sets what the standard design assumes. Without verification it is the code-level window of Section 150.1(c)3A, so a new window earns credit only if it beats that code-level window. With verification it is the existing U-factor and SHGC as verified.
What verification can be worth
The compliance manual uses a single-pane metal-framed window as its example. Verified, it counts as a 1.28 U-factor and 0.80 SHGC, which is substantial credit once the new window reaches 0.30 and 0.23. The U-factor matches the default in Table 110.6-A for an operable single-pane metal window. The credit can then offset a weak feature elsewhere in the remodel.
A worked example from the manual
An existing zone 12 house has all single-pane windows. About 300 square feet are replaced in existing openings, and one 30 square foot window becomes a pair of French doors totalling 40 square feet. That adds 10 square feet of fenestration, within the exception for up to 16 square feet added, so the total-area limits do not apply. The mandatory fenestration rules of Section 110.6 still do.
Timing and paperwork
Verification must happen before the old windows come out. Because it is a field-verified item, expect a registered CF1R. Section 10-103(a)1C lets a department waive documentation only where no field verification is required.
Small jobs have relief: up to 75 square feet of replacement needs only a U-factor of 0.40 or lower and, in zones 2, 4 and 6 to 15, an SHGC of 0.35 or lower (zone 15 has its own 0.23 limit), covered in windows and Title 24. For unrated windows see aluminum windows. Whole-remodel scope is in remodel Title 24, and attic questions in unknown insulation. Our residential Title 24 reports model both routes.
Common Title 24 Questions
- What is Title 24?
- Do I need a Title 24 report?
- How much does a Title 24 report cost?
- How long does a Title 24 report take?
- What is included in a Title 24 report?
- What plans do I need to upload?
Frequently Asked Questions
New glass in an existing sash or frame is a repair if it is at least equivalent to the original in performance. A new window unit is a replacement.
No. Verification is optional and only matters for the performance method.
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