Timber · Bracing & floors
Bracing walls: racking force and capacity calculator
Wind racking force on a house or shed in one direction from the area of the elevation (half the wall height plus the roof above) times the lateral wind pressure for the wind classification. Two bracing types with their lengths give the total capacity; the tool checks the capacity, reports the shortfall in metres of the stronger type, the tie-down force at each panel end and the maximum spacing between bracing walls.
Standard: AS 1684.2/.3 Section 8 bracing method: racking force = area of elevation × lateral wind pressure; bracing-unit capacities by type (Table 8.18, indicative values) · spacing of bracing walls ≤ 9 m
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Building dimension facing the wind | 14 | m |
| Wall height (top plate) | 2.7 | m |
| Roof height above the top plate | 1.8 | m |
| Lateral wind pressure on the elevation (AS 1684 tables) | 0.9 | kPa |
| Bracing type 1 | (h) Plywood, with end tie-down rods | |
| Length of type 1 | 6 | m |
| Bracing type 2 | (c) Two diagonal metal straps (tensioned) | |
| Length of type 2 | 4.8 | m |
| Largest spacing between bracing walls | 8.5 | m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Area of elevation | 44.1 | m² |
| Racking force | 39.7 | kN |
| Capacity type 1 (6 kN/m × 6 m) | 36.0 | kN |
| Capacity type 2 (1.5 kN/m × 4.8 m) | 7.2 | kN |
| Total bracing capacity | 43.2 | kN |
| Extra length of the stronger type needed | 0.00 | m |
| Tie-down per panel end (strongest type) | 16.2 | kN |
- ✓ Bracing capacity ≥ racking force — 109 %
- ✓ Bracing walls at ≤ 9 m centres
Method, formulas and assumptions
- Racking force = lateral wind pressure × area of elevation (half the storey height plus the roof), per AS 1684.2/.3 Section 8; the pressure depends on wind class, building width and roof pitch (Tables 8.1–8.5).
- Bracing capacities shown are indicative of AS 1684 Table 8.18 types: use the table (or the sheet manufacturer's tested values) for the exact system and fixing.
- Distribute bracing evenly, at both ends, and connect to the roof/ceiling diaphragm; ply panels need tie-down at each end.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.