Permeable Cladding Reduction Factor Kp
AS/NZS 1170.2:2011 • Clause 5.4.5 • Table 5.8 • External pressure
Quick reference — When is Kp = 1.00?
Kp = 1.00 for ordinary solid (impermeable) cladding
Examples: solid metal roof sheeting, solid metal wall panels, concrete walls and masonry walls. These surfaces do not qualify for a permeable-cladding reduction.
For windward and leeward walls: Kp = 1.00
Windward wall (W): Kp = 1.00. Leeward wall (L): Kp = 1.00. Side wall (S) and roof (R): Kp = 1.00 for solid cladding; a reduction is considered only for qualifying permeable cladding under suction.
| Surface / loading condition | Factor | Explanation |
|---|---|---|
| Solid metal roof sheeting | 1.00 | Impermeable roof cladding |
| Solid metal wall cladding | 1.00 | Impermeable wall cladding |
| Concrete or masonry wall | 1.00 | Solid, non-permeable surface |
| Windward wall / positive external pressure | 1.00 | No permeable-cladding suction reduction |
| Leeward wall | 1.00 | Not within the roof / side-wall table cases used in this calculator |
| Roof or side wall that fails the reduction eligibility conditions | 1.00 | Default: no reduction |
| Eligible permeable roof or side wall under negative pressure (suction) | Calculate | Table-based reduction may apply if the specified conditions are satisfied |
Important: A building having windows, doors or ventilation openings does not automatically make its solid roof or wall cladding permeable. Assess internal pressure Cp,i separately.
Selected surface: checking applicability…
1. Cladding and loading conditions
Table-based reduction is restricted to applicable roof and side-wall cases.
The reduction is considered for suction, not positive pressure.
Solid cladding: Kp = 1.0.
Clause 5.4.5: The factor Kp accounts for eligible permeable cladding under external wind suction. Do not confuse it with internal pressure Cp,i caused by building openings.
2. Solidity and building geometry
Solid projected area ÷ total projected area. Example: 0.995 = 99.5% solid.
Use the applicable along-wind dimension for Table 5.8.
Location of the cladding element along dₐ.
Eligibility check: The Table 5.8 reduction used here is restricted to a solidity ratio greater than 0.99 and less than 0.999. At or outside those limits, this calculator conservatively returns Kp = 1.0. Confirm the applicability and exact requirements against your licensed copy of AS/NZS 1170.2:2011.
3. Calculated Kp
Kp = —
4. Table 5.8 — Distance bands and Kp
| Zone | Distance from windward edge | Distance for entered dₐ (m) | Kp |
|---|---|---|---|
| 1 | 0 to 0.2dₐ | — | 0.90 |
| 2 | 0.2dₐ to 0.4dₐ | — | 0.80 |
| 3 | 0.4dₐ to 0.8dₐ | — | 0.70 |
| 4 | 0.8dₐ to 1.0dₐ | — | 0.80 |
0.900–0.2dₐ
0.800.2–0.4dₐ
0.700.4–0.8dₐ
0.800.8–1.0dₐ
Windward edge: 0Distance along wind direction →dₐ = 20 m
The strip represents the four distance bands for eligible cladding. The black marker shows your selected position x. For a cladding panel spanning multiple bands, check the governing applicable pressure rather than selecting only its centre point.
5. How Kp is used
External aerodynamic shape factor: Cfig,e = Cp,e × Ka × Kc,e × Kl × Kp, subject to the relevant provisions and restrictions of AS/NZS 1170.2:2011. The present calculator determines Kp only; it does not calculate the other factors or net wind pressure.
Engineering check: This tool follows the table values and eligibility assumptions stated above. Check the exact Table 5.8, Figure 5.4 and Clause 5.4.5 wording in the project-adopted Standard before relying on the output for design.
