Sustainable Building Guidelines - Wellington Conditions
View over Wellington. Photo by Murray Douglas
When building a sustainable home in Wellington there are many conditions specific to the city that should be taken into consideration.
Wind
Wellington is well known for its strong winds. Yearly average wind speeds are 7.5 metres per second at the airport. Most days there are gusts that exceed average speeds.
In terms of sustainability, Wellington’s strong winds can be utilised to generate renewable energy for use in homes and businesses. Wellington is well suited for wind energy as the average monthly wind speed does not alter much throughout the year.
Wellington’s many hills means that a number of sites are too sheltered from the wind to operate a wind turbine effectively, or the wind may be funnelled by external features so that the speeds are too high and would damage a turbine. Detailed wind and load analysis should be done by a suitable professional before decisions are made on wind turbine locations.
There are also potential environmental effects on neighbouring properties due to visual impact and noise, so it is important to meet the requirements of the Council’s District Plan.
Wind Protection
Planting at Pugh House
Wellington’s wind speeds must be taken into consideration when building a sustainable home. High wind speed causes heat loss from a building – in Wellington, southerly winds are generally colder than their northerly counterparts. Local characteristics like neighbouring buildings or certain landscape combinations may funnel or accelerate wind speed in a section’s direction.
Wind protection can be provided by:
- the topography of the area
- a tree shelterbelt
- neighbouring buildings
An effort should be made to locate a section with an existing shelter belt, or existing trees on the site that can be moved to provide protection. If new planting is needed, native trees and shrubs should be used since the high winds in Wellington can kill some introduced plant life.
Specific engineering design solutions might be required due to high wind at a site.
Topography
Wellington's hilly landscape. Photo by Murray Douglas
Wellington’s hilly topography presents challenges and opportunities for sustainable buildings.
The hills can affect solar access. North-facing slopes can provide good solar access for natural light, passive solar heating, and potential solar water heating. South-facing slopes can make it challenging to harness the sun’s energy.
One of the sustainability challenges of steep slopes is the potential for erosion. Rainfall, in addition to damaging the landscape, flushes loose sediment into watercourses, damaging aquatic life.
To minimise erosion, any earthworks should take place during the summer months.
A local resource on erosion is Greater Wellington’s guide to erosion and sediment control on small sites.
Erosion and sediment control for small sites - Greater Wellington Regional Council website
Temperature
Outside cladding on Pugh House
While Wellington winters are relatively mild, they still produce some cold days and nights. Double-glazed windows are ideal to keep heat inside homes.
New requirements under the Building Code (taking effect in Wellington on 30 June 2008) will make double-glazing almost mandatory in the Wellington region. The Standards New Zealand Handbook 4244 shows how to achieve various levels of thermal efficiency.
Wellington’s winter temperatures mean that hot water cylinders should be wrapped in insulation to avoid loss of heat. Pipework should also be insulated and reduced in length where possible.
Due to Wellington’s mild climate, overheating of houses in summer is not generally a problem. Tinted windows are not usually required, although homes with large westerly facing windows may require tinting.
Corrosion from Seawater
Even in the shelter of Wellington’s harbour, any home near water must be protected against corrosive seawater.
NZS 3604 (the New Zealand standard for the design and construction of timber-framed buildings) defines a sea spray zone as any area “within 500 metres of the sea including harbours, or 100 metres from tidal estuaries and sheltered inlets”. This definition incorporates a large portion of Wellington.
To prevent corrosion, stainless steel fixings, ties, nails and fastenings for any construction within 500m of the sea are recommended. NZS 3604 also recommends that houses further than 500 metres from the sea use stainless steel for the majority of fixings used in construction.
Rainfall cannot be relied upon to remove all corrosive build-up from your home. Ensure sheltered areas such as under verandas and eaves are cleaned regularly to prevent the build-up of corrosive agents like saltwater residue.
Soil & Drainage
Solar house
Wellington has a mixture of thin rocky and clay-based soils that are not particularly well-draining. Any natural storm water treatment and retention systems need to take this into account. The Council’s Drainage Office can provide more guidance on specific situations.
Rainfall
Wellington receives an average of 1200 – 1400 mm of rain per year, similar to the rest of the country. As a result of climate change, Wellington is expected to become even wetter over time. Most rain is in winter but heavy rain can happen at any time.
Rainwater harvesting for uses like watering gardens or flushing toilets can provide benefits of reducing the impact of rain on the storm water system and saving costs of treating and distributing drinking water.
Flooding can also be an issue in Wellington. Though not directly related to building design, it is a sustainability issue worth considering. Current flood hazard areas can be found on the Council’s District Plan maps.
Public Transport
Choosing a building site that is close to a public transport route, walkway or cycleway can decrease the need for private car use, reducing greenhouse gas emissions.
Earthquake Risk
Wellington’s location on a faultline means that there is a significant risk of earthquake damage. The Council’s District Plan maps show hazard areas for potential earthquakes as well as flooding.
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