This document contains diagrams and tables related to determining the maximum height of buildings based on wind speed factors. Diagram 6 shows a map of wind speeds in various regions. Table a provides a Factor O based on the orographic zone and slope of the terrain at a site. Factor O is used to calculate Factor S, which combines wind speed, terrain, and orography to determine the appropriate building height restrictions in Table c. The maximum allowable building height decreases as the Factor S increases due to higher wind speeds and steeper terrain.

1. 19
Approved Document A Structure
THICKNESS OF WALLS IN CERTAIN SMALL BUILDINGS A1/2
Diagram 6 Map showing wind speeds in m/s for maximum height of buildings
24.5
24
23.5
23.5
23
22.5
22.5
23
24.5
22
22
23
24
21.5
21.5
22.5
23.5
Note: A more detailed approach for obtaining Factor O is given by Figure 3 Diagram 6.
Figure 2 Orographic zones for Factor O
See para 2C16
O N L I N E V E R S I O N
O N L I N E V E R S I O N

2. 21
Approved Document A Structure
Diagram 7 Maximum height of buildings
Find the orographic
zone for the site from
Figure 2 Diagram 6 and
obtain Factor O from
Table a (or use Figure 3
Diagram 6)
Table c Maximum allowable building height in metres
2kmS 2 to 20km 50km 2km 2 to 20km 50km
15
11.5
8
5.5
4
3
≤ 25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
Notes: Table a – Outside of the zones shown in Table a, Factor O = 1.0.
Table b – For elevated sites where orography is significant a more accurate assessment of Factor A can be
obtained by using the altitude at the base of the topographic feature instead of the altitude at the site,
see Figure 2 Diagram 6 or, alternatively, Figure 3 Diagram 6.
Table c – i) Sites in town less than 300m from the edge of the town should be assumed to be in country terrain.
ii) Where a site is closer than 1km to an inland area of water which extends more than 1km in the wind
direction, the distance to the coast should be taken as 2km.
Interpolation may be used in Tables b and c.
15
13.5
11
8
6.5
5
4
3.5
3
15
15
14.5
11
8.5
6.5
5.5
4.5
3.5
3
15
15
15
15
12.5
10
8.5
7
6
5.5
4.5
4
3.5
3
15
15
15
15
15
12.5
11
9.5
8
7
6.5
5.5
5
4.5
4
3.5
3
15
15
15
15
15
15
13.5
11.5
10
87.5
7.5
6.5
6
5.5
5
4.5
4
3.5
3.5
3
Orographic category and average slope of whole
hillside, ridge, cliff or escarpment
Factor O
Zone 2 Zone 3Zone 1
1.0
1.07
1.13
1.20
0
50
100
150
200
300
400
500
1.00
1.05
1.10
1.15
1.20
1.30
1.40
1.50
1.0
1.05
1.10
1.15
1.0
1.12
1.24
1.36
Category 1: Nominally flat terrain, average slope 1/20
Category 2: Shallow terrain, average slope 1/10
Category 3: Moderately steep terrain, average slope 1/5
Category 4: Steep terrain, average slope 1/5
Table a Factor O
Obtain value
of Factor A
from Table b
Calculate value
of Factor S from:
S = V × O × A
Obtain maximum
allowable
building height
from Table c
THICKNESS OF WALLS IN CERTAIN SMALL BUILDINGS A1/2O N L I N E V E R S I O N
O N L I N E V E R S I O N