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Carpenter Red Seal Exam Prep · Question

When laying out floor joists for a standard residential subfloor, what is the typical 'on centre' spacing measurement from the wall or baseline to the first joist?

For a standard 1220 mm wide subfloor panel, the first joist usually starts at 15.25 inches (387 mm) from the edge of the rim joist or sill plate. This allows th

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Question: When laying out floor joists for a standard residential subfloor, what is the typical 'on centre' spacing measurement from the wall or baseline to the first joist?

Answer options:

  • 16 inches (406 mm)
  • 12 inches (305 mm)
  • 24 inches (610 mm) ✅ 15.25 inches (387 mm)

Correct answer: 15.25 inches (387 mm)

Explanation: For a standard 1220 mm wide subfloor panel, the first joist usually starts at 15.25 inches (387 mm) from the edge of the rim joist or sill plate. This allows the centre of the first joist, and subsequent joists at 406 mm on centre, to properly support the edges of the subfloor panels.

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