Insulation and Acoustical (C-2) · Lesson 3 of 5

Blown-In Attic Insulation: R-Value, Weight and Bag Count

"Blown-In Attic Insulation: R-Value, Weight and Bag Count" is lesson 3 of 5 in the Insulation and Acoustical (C-2) Learning Hub. It opens with "The Code Ties Loose-Fill to Weight" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. The Code Ties Loose-Fill to Weight
  2. Find the R-Value the Code Requires
  3. Read the Product's Bag Chart and Count Bags
  4. Cross-Check with Weight per Square Foot
  5. Install to Depth and to Count, and Keep It Safe

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Required R-value" through "Depth markers".

What you'll be able to do

  • Explain the main idea of "Blown-In Attic Insulation: R-Value, Weight and Bag Count" in plain language you can use on the exam.
  • Apply this step with confidence: "Read the Product's Bag Chart and Count Bags".
  • Apply this step with confidence: "Cross-Check with Weight per Square Foot".
  • Apply this step with confidence: "Install to Depth and to Count, and Keep It Safe".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Blown Attic Insulation: Bag Count from the ChartDepth marker 13.5 in.Ceiling joists and drywallAttic 30 ft x 40 ft = 1,200 sq ftOne depth marker per 300 sq ft (assumed): 4EXAMPLE CHART: R-38, 27.5-LB BAGChart: 13.5 in., 19 bags per 1,000 sq ftBags = 1,200 x 19 / 1,000 = 22.8Round UP: 23 bagsWeight: 23 x 27.5 = 632.5 lb632.5 / 1,200 = 0.527 lb per sq ftChart weight: 19 x 27.5 / 1,000 = 0.523Markers: 1,200 / 300 = 4 (assumed)23 bags AND 13.5 in. at all 4 markersDepth alone does not prove R-38: weight per sq ft must match the label (Energy Code 150.0(b)).Sources: 2025 Energy Code 150.0(b), Table 150.1-A (CZ 12: R-38). Chart values are illustrativeCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: The Code Ties Loose-Fill to Weight

Loose-fill insulation is sold by weight, and it fluffs up and later settles, so depth alone cannot prove the R-value. The 2025 California Energy Code says so directly: when loose-fill insulation is installed, the minimum installed weight per square foot shall conform with the insulation manufacturer's installed design weight per square foot at the manufacturer's labeled R-value (Section 150.0(b)). The bag chart on the product is where you find that design weight, so the bag count is a code check, not only a purchasing number.

Step 2: Find the R-Value the Code Requires

For a new single-family ceiling the mandatory floor is a U-factor not over U-0.043, or R-22 or greater for the insulation alone between wood framing; in an alteration, U-0.054 or R-19 (Section 150.0(a)2 and its exception). The prescriptive package is higher: Table 150.1-A, Option C ceiling insulation for vented attics is R-38 in Climate Zone 1 and 8 through 16, and R-30 in Climate Zones 2 through 7 (Option B ceiling insulation is R-38 except R-30 in Zones 3, 5, 6 and 7). Use the R-value on the plans or compliance documents, and remember the attic access door must have permanently attached insulation and be gasketed (150.0(a)3).

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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