Glazing (C-17) · Lesson 5 of 5

Storefront Energy Compliance: Area-Weighted Ratings

"Storefront Energy Compliance: Area-Weighted Ratings" is lesson 5 of 5 in the Glazing (C-17) Learning Hub. It opens with "What the Energy Code Asks of Glazing" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What the Energy Code Asks of Glazing
  2. The Three Ratings and the Window Area Limit
  3. Read the Right Row and Climate Zone in Table 140.3-B
  4. Do the Area-Weighted Average
  5. If One Average Fails

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Window area limit" through "Fix the failing average".

What you'll be able to do

  • Explain the main idea of "Storefront Energy Compliance: Area-Weighted Ratings" in plain language you can use on the exam.
  • Apply this step with confidence: "Read the Right Row and Climate Zone in Table 140.3-B".
  • Apply this step with confidence: "Do the Area-Weighted Average".
  • Apply this step with confidence: "If One Average Fails".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Storefront Energy Compliance: Area-Weighted RatingsABCA: 600 sq ft U 0.36 SHGC 0.24 VT 0.52B: 300 sq ft U 0.45 SHGC 0.30 VT 0.48C: 100 sq ft U 0.50 SHGC 0.28 VT 0.40Total storefront 1,000 sq ftWindow area: 1,000 / 4,000 sq ft of wall= 25 percent, under the 40 percent limitWORKED EXAMPLE: storefront, Climate Zone 9Area-weighted = sum(area x rating) / total areaU-factor (max 0.41):(600x0.36 + 300x0.45 + 100x0.50)/1,000= 0.401 OKRSHGC (max 0.26), no overhang so = SHGC:(600x0.24 + 300x0.30 + 100x0.28)/1,000= 0.262 FAILVT (min 0.46):(600x0.52 + 300x0.48 + 100x0.40)/1,000= 0.496 OKFix: B at SHGC 0.26 gives (144+78+28)/1,000= 0.250 OKAs specified the glazing FAILS on RSHGC: 0.262 is over 0.26U-factor and VT pass; switching product B to 0.26 SHGC passes all threeLimits from Table 140.3-B, curtain wall or storefront, CZ 9Source: 2025 California Energy Code 140.3(a)5, Table 140.3-B (Climate Zone 9), Subchapter 1 definitionsCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What the Energy Code Asks of Glazing

California Energy Code (Title 24, Part 6) Section 140.3(a)5 sets the prescriptive requirements for vertical windows in the exterior walls of nonresidential buildings. They limit window area, and they require an area-weighted average U-factor, an area-weighted average relative solar heat gain coefficient (RSHGC), and an area-weighted average visible transmittance (VT) that meet the numbers in Table 140.3-B for the climate zone. Subchapter 1 defines site-built fenestration as storefront systems, curtain walls, and atrium roof systems, designed to be field-glazed or field assembled, which describes the glazier's field-assembled work.

Step 2: The Three Ratings and the Window Area Limit

U-factor is the overall coefficient of thermal transmittance in Btu/(hr x sq ft x F), and the table sets a maximum. SHGC is the ratio of solar heat gain entering through the fenestration to the incident solar radiation, also a maximum in the table. VT is the ratio of visible light transmitted through the glazing; the higher the VT, the more light passes, and the table sets a minimum. Section 140.3(a)5A limits total window area to 40 percent of the gross exterior wall area (or 6 ft times the display perimeter, whichever is greater), and west-facing window area to the same 40 percent test applied to west-facing wall area. Table 140.3-B shows the maximum window-wall ratio (WWR) as 40 percent.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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