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BS 6399: Part 2: 1997
Loadings for Buildings 
Part 2. Code of practice for wind loads

Basic Wind Speed
The standard gives basic wind speeds for locations in the UK, the speeds are hourly mean wind speeds likely to be exceeded on average only once in 50 years
As an aid we have chosen a selection of towns throughout the UK, and determined the the basic wind speed.
If there is a town or towns that you would like to be included please let us know
Altitude Factor
The altitude factor Sa is used to adjust the basic wind speed for the altitude of the site above sea level. In preparation of the tables it has been assumed that there is no significant topography.
As a generalisation any building more than half-way up a hill, or an on a ridge or cliff will have increase wind loading. If your project falls into this category, then please contact us for a more detailed analysis.
In the preparation of the table 4 categories of height above sea level have been used
  • 0-50m
  • 51-100m
  • 101-150m
  • 151-200m
Direction Factor
The direction factor Sd has been taken as 1, which is suitable for buildings where the orientation is unknown or ignored. Where a more detailed analysis is required, please contact us.
Seasonal Factor
The seasonal factor Ss has been taken as 1, which is suitable for permanent buildings
Probability Factor
The probability factor Sp is taken as 1, which is equivalent to a return period of 50 years
Site Exposure
Two categories of ground roughness have been considered
  • Country
  • Town
The town category is defined as built-up areas with an average level of roof above ground level of at least 5m.
For a building to be considered as town, then the building must be at least 2km inside the town terrain.
The distance from the sea is required, for simplicity 4 categories have been use in the preparation of the tables
  • 2km
  • 10km
  • 50km
  • >100km
For buildings within 2km of the sea or estuary, a more detailed analysis will be required.
Building Height
The building height should be taken as the maximum height of the building above ground level.
The effective height (as defined in the standard) is taken as the actual building height.
Size Effect Factor
The size effect factor Ca has been taken as 1, i.e. a diagonal dimension of 5m
Pressure Coefficients
The following pressure coefficients have been used in the preparation of the tables
External (Cpe)
Flat Roofs
Zone A Zone B Zone C
-2 -1.4 -0.7
Monopitch Roofs
Pitch Zone A Zone B Zone C Zone D Zone E Zone F
5 -2.1 -1.2 -0.8 -1.1 -2.4 -1.1
15 -1.6 -0.9 -0.9 -1.1 -2.6 -1.0
30 -1.3 -1.0 -1.0 -1.2 -1.7 -1.0
Duopitch Roofs
Pitch Zone A Zone B Zone C Zone D Zone E Zone F
5 -2 -1.2 -0.6 -1.1 -0.9 -0.6
15 -1.6 -0.8 -0.6 -1.5 -1.3 -0.9
30 -1.2 -0.6 -0.6 -1.1 -0.9 -0.6
Exposure Case Zone A Zone B
Isolated -1.3 -0.8 +0.85
Funnelling -1.6 -0.9 +0.85
Note: If there is a building near to the building in question  and the distance between the buildings is less than a or b, then use the funnelling exposure (See Zones for definition of a and b)
Internal (Cpi)
+0.2 or -0.3  No dominant openings
For ease of use the zones as defined in the standard have been simplified as follows
Flat Roofflat roof
Monopitch Roofs
monopitch roof
Duopitch Roofs
Duopitch Roofs
Use of Tables
To use the tables:

1. Determine the wind loads from the building height

2. Calculate the Zone dimensions