Painting and Decorating (C-33) · Lesson 4 of 6

Interior Finish Classes: What Can Go on the Wall

"Interior Finish Classes: What Can Go on the Wall" is lesson 4 of 6 in the Painting and Decorating (C-33) Learning Hub. It opens with "Why a Painter Needs Chapter 8" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Why a Painter Needs Chapter 8
  2. Class A, B and C
  3. Thin Finishes Are Exempt
  4. Read Table 803.13 by Group and Location
  5. Attachment and Stability

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Convert each result to a class" through "Check whether a plain paint coat needs testing".

What you'll be able to do

  • Explain the main idea of "Interior Finish Classes: What Can Go on the Wall" in plain language you can use on the exam.
  • Apply this step with confidence: "Thin Finishes Are Exempt".
  • Apply this step with confidence: "Read Table 803.13 by Group and Location".
  • Apply this step with confidence: "Attachment and Stability".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Interior Finish: Class A, B, C by OccupancyCBC §803.1.2 CLASSESClass A: flame spread 0-25Class B: flame spread 26-75Class C: flame spread 76-200All classes: smoke-developed 0-450Paint under 0.036 in is exempt (§803.2)TABLE 803.13: R-2 NONSPRINKLEREDExit stairways, passageways: BCorridors, exit access stairs: BRooms and enclosed spaces: CSprinklered R-2: C in all threePRODUCTFS / SMOKECLASSSTAIRS+CORR (B)ROOMS (C)W20 / 300APassPassX70 / 350BPassPassY90 / 400CFailPassZ20 / 500noneFailFailW and X everywhere; Y in rooms only; Z nowhere (smoke index above 450)Source: 2025 CBC §803.1.2, §803.2, Table 803.13CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Why a Painter Needs Chapter 8

2025 CBC Chapter 8 governs materials used as interior finishes, trim and decorative materials (§801.1). Section 803 limits the fire performance and smoke development of interior wall and ceiling finishes by occupancy group and location. A painter or wallcovering installer is the person who decides what actually goes on the wall, so the finish has to match what the building's occupancy allows. The chapter also points to CALGreen Division 5.5 for the VOC rules on finish materials (§801.1).

Step 2: Class A, B and C

Under §803.1.2, finishes tested to ASTM E84 or UL 723 are grouped by flame spread index and smoke-developed index. Class A: flame spread 0-25, smoke-developed 0-450. Class B: flame spread 26-75, smoke-developed 0-450. Class C: flame spread 76-200, smoke-developed 0-450. A lower class letter is the safer product, and a smoke-developed index above 450 fits none of the classes. Finishes that pass NFPA 286 under §803.1.1.1 are treated as Class A (§803.13).

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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