Masonry (C-29) · Lesson 3 of 8

Chimney Height, Cricket, Spark Arrester and Clearances

"Chimney Height, Cricket, Spark Arrester and Clearances" is lesson 3 of 8 in the Masonry (C-29) Learning Hub. It opens with "The 3-2-10 Termination Rule" 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 3-2-10 Termination Rule
  2. Chimney Cap and Cricket
  3. Spark Arrester and Rain Cap
  4. Clearance to Combustibles and Fireblocking
  5. Walls, Cleanout and Flue Changes

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Use the higher result" through "Clearance".

What you'll be able to do

  • Explain the main idea of "Chimney Height, Cricket, Spark Arrester and Clearances" in plain language you can use on the exam.
  • Apply this step with confidence: "Spark Arrester and Rain Cap".
  • Apply this step with confidence: "Clearance to Combustibles and Fireblocking".
  • Apply this step with confidence: "Walls, Cleanout and Flue Changes".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Chimney Height: The 3-2-10 RuleELEVATION - SIDE VIEWridge 19.0 fttop 21.0 ft18.5 ft15.5 ft2 ft3 ft7 ft (within 10 ft)CHIMNEY HEIGHT CHECK (R1003.9)Roof at chimney 15.5 ft; ridge 19.0 ft3-ft rule: 15.5 + 3 = 18.5 ftRidge is 7 ft away (within 10 ft)2-ft rule: 19.0 + 2 = 21.0 ftSpark arrester (R1003.9.2):13 x 13 flue outlet = 127 sq innet free area ≥ 4 x 127 = 508 sq inCricket (R1003.20):48 in wide, 6:12 roof: H = W / 4H = 48 / 4 = 12 inChimney top 21.0 ft: 5.5 ft above the roof, 2 ft above the ridgeSpark arrester 508 sq in net free area; cricket 12 in highAirspace to combustibles: 2 in inside the building, 1 in if entirely outside (R1003.18)Source: 2025 CRC R1003.9, R1003.9.2, R1003.18, R1003.20, Table R1003.20; CBC 2113.9, 2113.19CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: The 3-2-10 Termination Rule

2025 CRC R1003.9 (CBC 2113.9) sets two tests for how high a masonry chimney goes, and the chimney must pass both. It extends at least 3 feet above the highest point where the chimney passes through the roof, and at least 2 feet higher than any portion of the building within 10 feet. Work out the top elevation each rule gives and build to the higher one. The 10-foot distance is measured horizontally from the chimney to the nearest part of the building, usually the ridge or a taller roof wall.

Step 2: Chimney Cap and Cricket

A masonry chimney gets a concrete, metal or stone cap sloped to shed water, a drip edge, and a caulked bond break around any flue liner (R1003.9.1). Where the chimney dimension parallel to the ridgeline is greater than 30 inches and the chimney does not intersect the ridgeline, a cricket is required, flashed and counterflashed like a normal roof-chimney joint (R1003.20). Table R1003.20 gives the cricket height H as a fraction of the chimney width W by roof slope: 12:12 is W/2, 8:12 is W/3, 6:12 is W/4, 4:12 is W/6, 3:12 is W/8.

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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