Site Analysis

Understanding all the features of a site, using and protecting the best, and minimising the impact of the worst.

Sun

By analysing the impact of the sun on a site, as well as the building’s location, the spatial arrangement, orientation, window placement, daylight access and other design features, the designer can take full advantage of passive solar design features and increase the energy efficiency and comfort of the building.

On this page:

  • assessing a site for sun
  • altitude and azimuth
  • solar radiation
  • building material durability
  • shade
  • sites with limited solar gain
  • locating information

Assessing a site for sun

When assessing a site for sun, consider:

  • the time during the day that the site receives sunlight
  • the sun's path at different times of the day and year
  • how the site’s shape, slope and orientation affect solar access
  • how obstructions such as adjacent buildings, trees and landforms will impact on the site and the potential design
  • the owners' lifestyle – for example, when they want to have sun or shade.

Sun paths

The simplest way to assess the passage of sun across a site is by observation. A site visit can also help identify site-specific conditions such as the impact of a tree or a ridgeline.

Sun path diagrams provide a broader overview of sun on a site as they map the path of the sun across the sky at different times during the day throughout the year. They can help establish the position of the sun relative to a site and can be used to determine the effect of shadows cast by buildings, trees and landforms on and around the site.

Sun path diagrams for New Zealand have been produced by the Victoria University of Wellington, Centre for Building Performance. In the diagrams, the centre is the point of observation and the arcs represent the sun’s altitude angle at different times of the day throughout the year, using a 24 hour clock (12 hours ahead of GMT), rather than solar time. They are accurate to approximately 1 degree north or south of the allotted latitudes but it is important to have accurate contour lines when using them.

 

Altitude and azimuth

The position of the sun with respect to an observer is commonly represented by two angles – altitude and azimuth.

Altitude is the angle of the sun’s rays compared with the horizon. At sunrise and sunset, the altitude is zero, and in the southern hemisphere, the maximum altitude of the sun at any specific location occurs at solar noon on 21/22 December (longest days of the year).


Azimuth (sometimes known as bearing) is the direction of the sun as shown on a compass. Sun bearings at sunrise and sunset at different New Zealand latitudes are available from Land Information NZ’s astronomical information.

Solar radiation

Solar or ultraviolet (UV) radiation is the energy from the sun. The amount of solar radiation available on a site depends on the latitude and the sunlight hours received.

Information about UV levels can be obtained from NIWA’s UV Atlas which provides information about UV levels around New Zealand since 1960.

Solar radiation data for typical reference years for Kaitaia, Auckland, Wellington, Christchurch and Invercargill is also available from the Energy Efficiency and Conservation Authority’s Solar Water Heating Guidebook: A Technical Guide for Building Professionals (PDF, 1.35MB).

Building material durability

UV radiation affects the durability of many materials. Colours fade, plastic-based materials may become brittle, timber moves and twists, and expansion and contraction from heating and cooling places stress on many materials, so the effect of UV radiation over a building’s lifetime must be considered.

Select materials with a higher UV index number (when available) as they are more resistant to UV degradation (such as fading).

Shade

Shade is often required in the summer, but in most parts of the country, winter sun is desirable. Obstructions on a site may block sunlight access at times when it is required.

When considering sunlight and building design, assess the impact of obstructions in the future as well as the present. For example, a small tree on an adjacent site may grow into a large one that blocks sun, a building may be erected on a currently vacant site or an existing building may be demolished and replaced by a larger one.

Alternatively, existing trees may be retained for summer shade.

Sites with limited solar access

South and east-facing, sloping sites have limited solar access. It is difficult to utilise effective passive solar design features on these sites, and they should generally be avoided. Where it is not possible to avoid or the site is an otherwise desirable one (e.g. if it has excellent views), careful consideration of design including building location (e.g. locate as high as possible on the site), orientation and use of skylights/clerestories can maximise the benefits of solar access.

Locating information

The National Institute of Water and Atmospheric Research (NIWA) provides climate station data for its 30 climate stations throughout New Zealand, including information about sunshine hours and mean temperatures.

Aerial photographs can provide information about the buildings and vegetation on adjacent sites and may provide some limited information about the impact of sun on a site. This will depend on the age of the photo as in older photos, trees may have grown. Aerial images can be obtained from local councils, Google Earth and Terranet.

Sun impact information is also available:

  • by carrying out an on-site survey to establish levels of adjacent buildings and site features.
  • obtaining plans of neighbouring buildings from local councils.