Floor Framing Systems
Floor joist layout, blocking, bridging, rim joists, subfloor installation, and engineered floor systems.
- Calculate floor joist sizing based on span, spacing, and species
- Explain the purpose of blocking, cross-bridging, and rim joists in floor framing
- Describe proper subfloor installation techniques
- Identify engineered floor systems including I-joists and floor trusses
Leçon 1
Floor Joist Layout & Sizing
Floor Framing Overview
Floor framing creates the structural platform that supports all loads above - walls, furniture, occupants, and the roof. The system consists of joists, beams, posts, blocking, and subfloor - all working together to create a strong, level surface. The purpose of blocking in floor framing is to stiffen joists and prevent twisting, while the subfloor provides a structural surface over floor joists.
Joist Sizing
Floor joist size depends on the span, spacing, species, grade, and load requirements. The NBC provides span tables that specify the maximum allowable span for each combination.
| Joist Size | 16" OC Span (typical) | 24" OC Span (typical) |
|---|---|---|
| 2x6 | 8-9 feet | 7-8 feet |
| 2x8 | 11-13 feet | 10-11 feet |
| 2x10 | 14-16 feet | 12-14 feet |
| 2x12 | 17-20 feet | 15-17 feet |
The typical span for a standard floor joist is 10-16 feet depending on size and species. A 2x10 floor joist at 16 inches OC can typically span 12-16 feet depending on species and grade. Always consult the NBC span tables for the specific species, grade, and loading conditions.
Minimum Bearing
The minimum bearing for floor joists on a sill plate is 1-1/2 inches. This means the joist must rest on at least 1-1/2 inches of the sill plate or beam. In practice, most joists bear on the full width of the sill plate.
Joist Bearing
The minimum bearing for floor joists on a sill plate is 1-1/2 inches. This equals the thickness of a 2x member laid flat - the absolute minimum supported contact area.
Layout Procedure
Floor joist layout starts from one end of the building:
- Mark the first joist position 16 inches from the outside of the rim joist
- Continue marking every 16 inches (or 24 inches for wider spacing)
- Mark an "X" on the side of the line where the joist sits
- Account for openings (stairwells, chimneys) with doubled trimmers
Floor joist span depends on size, spacing, species, and grade - consult NBC span tables. The minimum bearing on a sill plate is 1-1/2 inches. Standard spacing is 16 inches on center.