Sometimes, customers enquire about a shed we’ve got advertised and are perplexed when their quote is more than our advertised price. This usually comes down to one thing: the site.
Every SHEDS4U kit is designed specifically for where it’s going to be built. We also, always, design to meet High Wind Zone construction requirements as standard, rather than sending out a one-size-fits-all kit and hoping for the best.
Some other suppliers will happily sell you exactly what you ask for – even if it’s not right for your location – and leave any problems (and costly fixes) up to you later. That can end up being frustrating and expensive.
It’s because we design every shed to suit its actual site conditions that the final price for your shed may differ from the advertised base price. Wind can be one of the biggest reasons for that.
Wind and why it matters for shed design
Wind direction, speed, and how often it blows, all have a big influence on building design. These factors affect things like:
- bracing requirements
- roof and wall cladding selection
- weathertightness detailing
- where doors and building entries are located
- window size and placement
- shelter for outdoor spaces
To understand this properly, let’s take a look at:
- designing for wind
- wind regions and zones
- specific design
- gathering information about local wind conditions
Designing for wind
In most cases, designing for wind means providing shelter. However, in hot or humid climates, buildings may be deliberately designed to let cooling breezes through to create a passive cooling effect.
It’s important to assess wind effects early in the design process. This includes understanding:
- wind speed (both average and peak)
- wind direction
- how wind affects the site at different times of the year
Getting this right early can save time, money, and headaches later on.
What affects wind speed on a specific site?
Wind speed isn’t just about your region — it’s also about what’s happening right around your site. The main influencing factors include:
General wind speeds in the region
These are typically sourced from:
Level of site exposure
This is best determined through on-site observation.
Terrain
Wind speed will:
- increase as it passes over or between hills
- slow down over rougher terrain due to drag
- accelerate over open, flat land or water
Nearby large bodies of water (sea or lake)
During the day, the land heats up faster than water. As warm air rises over land, cooler air from the water moves in, creating afternoon on-shore breezes.
Adjacent buildings and vegetation
Wind speed:
- is lower when a site is surrounded by taller buildings
- increases when wind funnels between buildings
- is slowed by trees and vegetation
Building height
The taller the building, the more exposed it is to stronger winds — especially if it’s higher than nearby buildings or vegetation.
Understanding prevailing wind direction
Prevailing wind direction is especially important when deciding:
- door and opening window locations
- shelter for outdoor areas
Other wind characteristics to consider include:
- the direction of the strongest winds
- the direction of the coldest winds
- humid versus dry winds
- winds coming off the sea (salt spray issues)
- wind directions that bring the most rain
Wind regions and zones in New Zealand
You can find out which wind zone your property sits in using official wind zone resources, like this one here.
NZS 3604 requires all buildings to be designed to withstand the winds they’re likely to experience. Bracing must be calculated separately for wind and earthquake loads, and the structure must be designed for whichever load is greater.
Under NZS 3604, the amount of bracing required depends on the design wind speed.
New Zealand is divided into:
- two wind regions (A and W)
- several lee zones, where landforms cause localised wind acceleration
Wind zone classifications (NZS 3604)
Wind zones are classified based on maximum ultimate limit state wind speeds:
- Low: below 32 m/s
- Medium: 37 m/s
- High: 44 m/s
- Very high: 50 m/s
- Extra high: 55 m/s
- Specific design (SD): over 55 m/s
How wind zones are determined
Table 5.1 in NZS 3604 outlines the steps required to determine a site’s wind zone:
- determine the wind region
- determine whether the site is in a lee zone
- determine ground roughness
- determine site exposure
- determine topographic class
In practice, wind zones can be established in several ways, listed below from most to least precise:
- site-specific calculations using AS/NZS 1170.2:2021 Wind actions
- site-specific calculations using NZS 3604:2011
- council wind maps (if based on current standards)
- BRANZ Maps
When specific design is required
The wind zones in NZS 3604 are based on simplified assumptions about wind direction, topography, and shelter. In some situations, these classifications may overestimate or underestimate actual site wind speeds.
In these cases, engaging an engineer to assess the site can be a more cost-effective option. Specific engineering design is required where wind speeds exceed 55 m/s.
Gathering information about local wind conditions
A site visit can provide valuable insight into wind behaviour. Look at vegetation and surrounding features, and have a chat with neighbours about how wind affects their properties.
Common signs of high wind exposure include:
- lack of established planting
- stunted trees or shrubs
- windbreak fences on nearby properties
- visible wind shaping of vegetation
Local councils can often provide wind zone information, sometimes online. A Land Information Memorandum (LIM) may also include wind zone details.
NIWA provides climate station data from 30 locations around New Zealand, including:
- wind speeds
- number of gale days per month
- wind roses showing historical wind patterns
Corrosion zones and environmental exposure
Atmospheric corrosion severity is classified into five groups based on corrosion rates of mild steel, as defined in AS/NZS 2312 and ISO 9223:
- Zone A: very low (not applicable in New Zealand)
- Zone B: low
- Zone C: medium
- Zone D: high
- Zone E: very high
To align standards, NZS 3604 has redefined exposure zones:
- sea spray zone is now zone D
- zone 1 is now zone C
- zones 2 and 3 are now zone B
Sea spray zones and coastal exposure
The sea spray zone includes all offshore islands and areas within 500 m of the coastline. This is classified as zone D under NZS 3604:2011.
However, areas very close to exposed beachfronts with heavy surf can experience extremely high corrosion due to salt deposition. These areas are classified as zone E under AS/NZS 2312 and ISO 9223. NZS 3604 requires the same corrosion protection for both zones D and E.
Geothermal areas and micro-climates
The geothermal zone used in NZS 3604:1999 no longer exists in NZS 3604:2011. Most geothermal areas now fall under zone B, but this does not mean corrosion risk is low.
Areas within 50 m of geothermal hot spots (such as bores, mud pools, or steam vents) can experience much higher corrosion rates. These are treated as micro-climates and require specific engineering design (SED).
NZS 3604 recognises that micro-climates can significantly affect durability. Even within the same building, corrosion rates can vary depending on shelter, salt accumulation, rainfall exposure, and local pollutants.
Where micro-climatic effects outweigh broader regional conditions, NZS 3604 recommends selecting materials suitable for a more severe exposure zone.
As always, if things get too complicated and you need advice or assistance, the SHEDS4U team is here to help.
