Sliding Glass Door Replacement: Title 24 Requirements
A sliding glass door is a glazed door, so it is judged as a window and not under the 0.20 swinging-door limit. A same-area replacement meets the zone values or the 75 square foot relief (U-0.40, SHGC 0.35). No default value in the tables reaches 0.40, so a slider without an NFRC rating cannot use that relief.
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Why a slider is judged as a window
Section 100.1 calls an exterior door with 25 percent or more glass a glazed door, and glazed doors must meet the fenestration product rules. The manual says most sliding glass doors fall in that group. The 0.20 U-factor limit in Section 150.1(c)5 is written for swinging doors and expressly leaves glazed doors out, so a slider follows the window rules in new windows and Title 24 instead.
The numbers a replacement slider carries
Section 150.2(b)1B applies to a slider replacing the same area: the Table 150.1-A values for the zone, or under Exception 1 up to 75 square feet of replacement glass at U-0.40 and SHGC 0.35 (zone 15 stays at 0.23). Door area is the whole rough opening, frame included, so a 6 foot by 6 foot 8 inch opening is about 40 square feet, more than half of that allowance in one door.
If the door has no rating
Table 110.6-A gives glazed doors these defaults: metal frame 1.25 single pane or 0.77 double pane, thermal break 0.59, and nonmetal 0.99 single or 0.53 double. All are above 0.40, which is why a metal-framed slider with no NFRC rating cannot pass on its own; see aluminum windows.
Wide sliding walls are site-built
The manual's 2022 text counts large-track sliding glass walls as site-built fenestration. These carry an NFRC label certificate instead of a temporary label, may use the Appendix NA6 alternative defaults for up to 250 square feet or 5 percent of floor area, whichever is larger, and have no air leakage test, though they must still be weatherstripped and caulked. A manufactured slider must leak no more than 0.3 cfm per square foot at 75 pascals.
One more case
The manual's sunspace example treats a weatherstripped glass slider as one way to close off an unheated room and keep it unconditioned; see sunroom Title 24. For the swinging equivalent, read French door replacement, and our residential reports handle the glazing calculation.
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
No. The 0.20 limit applies to swinging doors that are not glazed doors. A slider with 25 percent or more glass follows the window U-factor and SHGC values.
Under 25 percent glass it is an opaque door, and the glazing is ignored in the prescriptive approach. Most patio sliders are well over that line.
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View all Windows and Doors guides → · Windows and Building Envelope · Title 24 guide