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 halfway 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
 050m
 51100m
 101150m
 151200m

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

The town category is defined as builtup 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

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 

Walls
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 
Zones 
For ease of use the zones as defined in the
standard have been simplified as follows 
Flat Roof 
Monopitch Roofs

Duopitch Roofs


Use of Tables 
To use the tables:
1. Determine the number of fixings from the building height
2. Calculate the Zone dimensions 