Roofing (C-39) · Lesson 1 of 6

Roof Area, Squares, and Shingle Bundles

"Roof Area, Squares, and Shingle Bundles" is lesson 1 of 6 in the Roofing (C-39) Learning Hub. It opens with "A Roofing Square Is 100 Square Feet" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. A Roofing Square Is 100 Square Feet
  2. Footprint Is Not Roof Area
  3. The Slope Factor Turns Footprint Into Roof Area
  4. Add Waste, Then Round Up to Whole Bundles
  5. The Method and the Sanity Check

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Footprint including overhangs" through "Convert to bundles and round up".

What you'll be able to do

  • Explain the main idea of "Roof Area, Squares, and Shingle Bundles" in plain language you can use on the exam.
  • Apply this step with confidence: "The Slope Factor Turns Footprint Into Roof Area".
  • Apply this step with confidence: "Add Waste, Then Round Up to Whole Bundles".
  • Apply this step with confidence: "The Method and the Sanity Check".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Roof Area, Squares, and Shingle BundlesROOF PROFILE: 6:12 PITCHSLOPE LENGTH13.42 inRISE 6 inRUN 12 in of footprintSlope factor = 13.42 / 12 = 1.118WALK THE NUMBERSFootprint with 2 ft overhangs:(40 + 2 + 2) x (30 + 2 + 2) = 44 x 34= 1,496 sq ftRoof area = 1,496 x 1.118= 1,672.5 sq ftSquares = 1,672.5 / 100 = 16.73With 10% waste: 16.73 x 1.10 = 18.40Bundles = 18.40 x 3 = 55.2ORDER 56 BUNDLES (round up)1,496 sq ft footprint x 1.118 = 1,672.5 sq ft = 16.73 squares18.40 squares with waste x 3 bundles = 56 bundles1 square = 100 sq ft (CSLB C-39 Study Guide; CRC R905.2.8.1 states weights per 100 sq ft).Slope factor = √(rise² + 12²) / 12. Bundles per square and waste % are bid practice, not code numbers.CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: A Roofing Square Is 100 Square Feet

Roofing is estimated, bid, and sold in squares, and the CSLB C-39 Study Guide asks it directly ("how many squares of roof covering are required?"). One square equals 100 square feet of roof surface, so a 2,500 sq ft roof is 25 squares. The California codes use the same 100-square-foot unit when they state roll roofing weight: base flashing may be mineral-surfaced roll roofing weighing not less than 77 pounds per 100 square feet (2025 CRC R905.2.8.1; 2025 CBC 1507.2.8.1), which is 77 lb per square. How many bundles of shingles make a square depends on the product, so read the wrapper. Bundles per square is bid practice, not a number printed in any California code book.

Step 2: Footprint Is Not Roof Area

A pitched roof is tilted, so its surface is larger than the footprint it sits over. Start with the footprint measured to the outside edge of the eaves and rakes, because shingles run out to the drip edge that the code requires at eaves and rake edges (2025 CRC R905.2.8.5), not just to the wall. Measuring only wall to wall is the classic way to under-order.

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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