Local Pressure Factor (Kl)

The local pressure factor (Kl) is an important design consideration required by the Loadings Standard. The peripheral areas of roof and wall surfaces are subjected to greater uplift loads than the main body of the roof. Designers need to include local pressure factors in the calculation of wind loads on the cladding.

When determining fixing requirements to NZS 1170.2, the engineer should prepare a roof map showing purlin spans and local pressure factors for each section of the cladding.

When designing to NZS 1170 the local pressure factors are:

• 1.5—applied to the edges of all buildings at a dimension equal to 0.2 or 20% of the width or height of the building whichever is the least.
• 2.0—applied to the edges of all buildings at a dimension equal to 0.1 or 10% of the width or height whichever is the least.
• 3.0—applied to roof pitches less than 10°, at the corners where the dimensions in (a) intersect. It also applies to corners of walls where the building height is greater than the building width.

Local Pressure for Low-Pitch Roofs

Local pressure A