Sunny Drafting & Design
In California, Title 24 window U-factor SHGC requirements determine whether a fenestration specification clears energy compliance before a permit is issued, and Bay Area projects face some of the state's more specific climate zone boundaries. Our team at Sunny Drafting & Design prepares Title 24 energy calculations for residential and commercial projects across San Jose, San Francisco, Oakland, and surrounding cities, and window compliance appears as a plan check correction more often than most project teams expect.
The California Energy Commission publishes the Building Energy Efficiency Standards that govern these limits, and the current edition tightened U-factor and solar heat gain coefficient thresholds compared to earlier cycles. Knowing which climate zone a parcel occupies, and which compliance path a project follows, determines every window specification on the construction documents.
Projects that choose between the prescriptive versus performance compliance path encounter very different flexibility when specifying windows. The prescriptive path imposes hard maximum values for U-factor and SHGC by climate zone, while the performance path allows envelope tradeoffs as long as modeled energy use stays within the calculated budget. Our team evaluates both options before locking in a fenestration schedule on any Bay Area project.
Contents
U-Factor vs. SHGC: Understanding the Two Core Metrics
What U-Factor Measures in Fenestration
U-factor quantifies the rate of heat transfer through a window assembly, expressed per hour, per square foot, and per degree Fahrenheit of temperature difference across the assembly. Lower U-factor values indicate better thermal resistance, and California requires National Fenestration Rating Council (NFRC) whole-unit certified values on all Title 24 submittals. The distinction between whole-unit ratings and center-of-glass ratings matters considerably, because whole-unit ratings account for the frame and edge spacer in addition to the glass lite itself. Our team regularly sees permit packages that reference a glazing manufacturer's center-of-glass performance rather than the NFRC whole-unit label, and plan checkers across Bay Area building departments flag that substitution consistently as a compliance deficiency.
What SHGC Controls in a Bay Area Climate
Solar heat gain coefficient measures the fraction of incident solar radiation that passes through a window into the conditioned space, expressed as a value between zero and one. A lower SHGC blocks more solar energy and reduces cooling loads, but Bay Area climate zones are predominantly heating-dominated rather than cooling-dominated, creating a genuine design tension. Restricting SHGC limits passive solar gains that would otherwise offset winter heating energy, and the performance compliance path allows the energy model to credit those gains under favorable orientations, giving south-facing projects measurably more flexibility than the prescriptive tables allow.
Pro insight: Our team recommends triple-pane low-e glazing for north- and east-facing windows in Climate Zone 3, where the heating-season thermal benefit consistently outweighs the added product cost across a typical project's energy payback period.
Bay Area Climate Zone Limits at a Glance
Prescriptive Thresholds by Climate Zone
Most Bay Area cities fall within Climate Zones 3 and 4 under the California Energy Commission's boundary maps. Coastal cities including San Francisco, Daly City, and Half Moon Bay sit in Zone 3, while inland cities such as San Jose, Fremont, and Walnut Creek fall in Zone 4. The prescriptive thresholds differ between these two zones, and our team confirms the correct zone assignment against the parcel address before beginning any energy calculation. The table below summarizes the current prescriptive limits for the assembly types our team encounters most frequently on Bay Area residential permit sets.
| Assembly Type | CZ 3 Max U-Factor | CZ 3 Max SHGC | CZ 4 Max U-Factor | CZ 4 Max SHGC |
|---|---|---|---|---|
| Vertical Windows (Fixed & Operable) | 0.30 | 0.23 | 0.30 | 0.25 |
| Skylights | 0.55 | 0.30 | 0.55 | 0.30 |
| Glazed Doors (≥50% glass area) | 0.30 | 0.23 | 0.30 | 0.25 |
| Opaque Doors (<50% glass area) | 0.20 | N/A | 0.20 | N/A |
These thresholds apply under the prescriptive path for low-rise residential projects, including ADUs. Our guide on Title 24 compliance for ADUs in the Bay Area covers how these fenestration limits integrate with accessory dwelling unit designs, where smaller floor plates can make individual window selections disproportionately influential on the overall energy calculation outcome.
Skylights and Glazed Doors
Skylights carry a more lenient U-factor allowance than vertical windows because their horizontal and low-pitch orientations receive more direct solar exposure, and the thermal dynamics are handled separately in the energy model. Glazed doors with more than fifty percent glass area are classified as windows for Title 24 purposes, which means sliding glass doors and most French door assemblies must meet the same 0.30 U-factor threshold as operable and fixed windows. Our team includes all glazed door schedules explicitly in the fenestration summary on the CF1R Certificate of Compliance — a step that some permit packages skip and that generates a correction on first review.
Warning: Sliding glass doors with decorative divided-light grilles frequently carry whole-unit NFRC ratings above 0.30, and our team always verifies the certified label before including any door assembly in a prescriptive-path submittal.
Mistakes That Cause Window Failures at Plan Check
Missing or Misread NFRC Labels
Plan checkers in San Jose, San Francisco, and Oakland consistently flag fenestration schedules that reference a glazing manufacturer's glass specification rather than the whole-unit NFRC rating, and this single error accounts for a significant share of the window-related corrections our team sees returned from building departments. Manufacturers publish NFRC whole-unit certified values in their product specification sheets and on window labels installed on shipped units. Our team cross-checks those ratings against the window schedule before transmitting the energy compliance package. Our post on CF1R vs CF2R vs CF3R compliance forms details exactly where whole-unit fenestration ratings must appear on each form for a complete and reviewable submittal.
Incorrect Climate Zone Assignment
The boundary between Climate Zones 3 and 4 cuts through several Bay Area cities, including portions of Fremont and San Jose, and a project located on the wrong side of that boundary faces different prescriptive thresholds. A single climate zone misassignment can invalidate an entire energy compliance package, requiring full recalculation and resubmittal, which adds material time to the permit timeline. Our team uses the California Energy Commission's official climate zone lookup and documents the confirmation method in the calculation notes so that the plan checker can verify the assignment without sending a correction. For room additions that span a zone boundary, our team applies the zone covering the majority of conditioned floor area.
- Confirm climate zone using the CEC's official address lookup before beginning any energy calculation
- Document the confirmation method in the calculation notes so plan checkers can verify the assignment without issuing a correction request
How to Specify Compliant Windows on a Permit Set
What the CF1R Form Requires
The CF1R Certificate of Compliance must include a complete fenestration schedule listing each window and glazed door type, its rough-opening area in square feet, orientation, whole-unit U-factor, and whole-unit SHGC. Our team structures the fenestration schedule to match the window and door schedule on the architectural drawings exactly, so that plan checkers can cross-reference both documents without ambiguity. Projects with multiple window types — a routine situation in new construction and room additions — require one row per window type in the schedule, not one row per individual opening. For more on how energy calculations integrate into the full permit package, our post on the role of Title 24 energy calculations in a California permit set provides the surrounding context that often informs how our team sequences deliverables.
Coordination Between Architecture and Energy Compliance
Window specifications should be finalized before the energy calculations are completed, because a product substitution after the CF1R is submitted requires a revised calculation and, in most Bay Area jurisdictions, a revised plan check submittal with associated fees and queue time. Our team advises that window selection happen in parallel with architectural design rather than after construction documents are otherwise complete, a sequencing discipline that prevents late-stage specification changes and the delays they introduce. For ADU projects specifically, our detailed breakdown of how ADU projects require both structural engineering and Title 24 compliance illustrates how the two disciplines share a permit timeline and why early coordination between them reduces overall delivery time.
Pro insight: Our team builds a preliminary fenestration schedule during schematic design so that window product selection stays within the compliance envelope from the outset, eliminating the substitution requests that arrive after calculations are finalized.
Frequently Asked Questions
Under the prescriptive path, vertical windows in both Climate Zone 3 and Climate Zone 4 must not exceed a whole-unit U-factor of 0.30. California requires NFRC-certified whole-unit ratings; center-of-glass values are not accepted for Title 24 compliance, and our team verifies the distinction on every fenestration schedule before submittal.
Both Climate Zone 3 and Zone 4 carry SHGC limits under the prescriptive path, but Zone 4 allows 0.25 while Zone 3 requires the stricter 0.23 maximum. In heating-dominated coastal zones, a tighter SHGC limit also restricts passive solar gains, which is why the performance path often produces better outcomes for projects with significant south-facing glazing area.
Skylights have separate prescriptive thresholds — a maximum U-factor of 0.55 and a maximum SHGC of 0.30 in both Climate Zones 3 and 4 — which are more lenient than vertical window limits on U-factor but apply the same SHGC category. Our team lists skylights in a separate row on the CF1R fenestration schedule to ensure clear review by the plan checker.
The performance path allows envelope tradeoffs, so a project with high-performance wall insulation or an efficient HVAC system may qualify to use windows that exceed prescriptive limits, provided the energy model demonstrates that total energy use stays within the allowed budget. Our team models both compliance paths to determine which produces the most cost-effective specification for a given project.
Final Thoughts
Getting Title 24 window U-factor SHGC requirements right from the start prevents the correction cycles that delay Bay Area permit approvals, and our team at Sunny Drafting & Design brings that precision to every energy calculation package we prepare. Anyone planning a new construction project, room addition, or ADU in the Bay Area is welcome to reach out to our team — we will confirm the correct climate zone, review the preliminary fenestration schedule, and deliver a complete CF1R package built to clear plan check on the first submission.
