Church Truss Types
| Type | Span | Application |
|---|
| Common (Fink/Howe) | 6–14 m | Classrooms, offices, utility |
| Scissor | 10–22 m | Sanctuary vaulted ceilings |
| Parallel Chord | 8–16 m | Flat/low-slope roofs |
| Attic | 8–12 m | 2nd-storey classrooms, storage |
| Mono | 4–10 m | Clerestory, lean-to, canopies |
| Hip Set (Girder) | Per span | Hipped entries, porticos |
Scissor bottom chord slope = 1/2 top chord slope (e.g., 6/12 top = 3/12 bottom). Girder trusses are multi-ply, crane-set individually.
TPIC Bracing Requirements
Temporary Bracing
| Element | Requirement |
|---|
| First truss | Ground-braced at 45°, 3 points (peak + quarter-points) |
| Top chord lateral | 2×4 on edge, max 2400 mm intervals, 2×16d per truss |
| Diagonal bracing | Top chord to bottom chord of adjacent, every 6 m max |
| Bottom chord lateral | 2×4 at 2400 mm intervals (critical for scissor) |
Permanent Bracing
- CLB: Continuous lateral bracing per truss engineer drawings
- T-reinforcement: 2×4 "T" block at every CLB/truss crossing
- Web bracing: Long compression webs braced at mid-height
- Do NOT strip temp bracing until all sheathing + permanent bracing complete
Connections & Bearing
| Item | Value |
|---|
| Min. bearing on wood plate | 89 mm (3-1/2") |
| Hurricane ties | Both bearings, every truss (Simpson H2.5A) |
| Hurricane tie nails | 8–10 nails per clip per manufacturer |
| Toenailing at bearing | 2×16d each side minimum |
| Jack rafter to hip/valley | 3×82 mm nails per jack minimum |
Truss heel must be fully on plate — no overhang, no gap. Heavy trusses may need custom steel bearing connectors per P.Eng.
Rafter Framing Essentials
Birdsmouth Rules
- Seat cut depth: max 1/3 rafter depth
- Seat cut width: match plate width for full bearing
- Always install crown up
- Leave tails long; snap chalk line to trim for straight fascia
Ridge Board vs. Ridge Beam
| Feature | Ridge Board | Ridge Beam |
|---|
| Structural? | No (nailing surface only) | Yes (carries rafter loads) |
| Requires ties? | YES — ceiling joists or rafter ties | No (beam carries load) |
| Support | N/A | Posts to foundation |
| Min. depth | ≥ rafter plumb cut depth | Per P.Eng. design |
Collar Ties vs. Rafter Ties
| Member | Position | Function |
|---|
| Rafter ties | Lower 1/3 | Resist horizontal thrust |
| Collar ties | Upper 1/3 | Prevent ridge separation ONLY |
Collar ties do NOT resist thrust. Rafter ties or ceiling joists required for that.
Code References
- TPIC: Truss Plate Institute of Canada — bracing requirements
- CSA O86: Engineering design in wood — truss/rafter design
- OBC Part 4: Structural design — all church roof framing engineered
- OBC Part 9: Prescriptive rafter tables, collar/rafter tie spacing
- Ont. Reg. 213/91: Fall protection, crane operations, scaffold requirements
- CSA Z150: Crane hand signals
Safety — Do Not Forget
- NEVER modify a truss without sealed P.Eng. written approval. No cutting, notching, drilling, or removing webs.
- Fall protection mandatory during all roof framing (Ont. Reg. 213/91).
- Crane lift plan for all truss setting. One signaller only. Clear exclusion zone.
- #1 failure cause: Missing permanent bracing. Install EVERY piece shown on truss drawings.
- Do not stack materials on stored trusses — damages connector plates and webs.
- Domino collapse risk: Inadequate temporary bracing causes progressive failure of entire truss row.
Pro Tips
- First truss: Crane does not release until ALL ground braces are secure. 3 brace points minimum.
- Hurricane ties on every truss at both bearings — even where not specifically drawn. $4 clip vs. truss lifting off in windstorm.
- Pattern rafter: Select straightest lumber. Test-fit before cutting production rafters.
- Connector plates: Inspect on delivery. Any popped, buckled, or gapped plates = engineering assessment required.