Site Analysis

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

Sun

The sun will influence the building’s location on a site, as well as the building’s spatial arrangements, orientation, window placement, daylighting and other aspects of design. By understanding the impact of the sun on a site, you’ll be able to use passive solar design features to make the building more energy efficient and comfortable for its occupants. You’ll also be able to make more efficient use of solar panels.

Solar radiation (UV) can also affect the durability of some building products, and therefore should be considered when you make your material choices.

When you’re assessing a site for sun, consider:

  • the period during the day that the site receives sunlight
  • the sun’s path – what direction the sun comes from at different times of the day and year
  • the site’s shape, slope and orientation
  • the impact of any obstructions such as neighbouring buildings, trees, and landforms on the design (see site use); for example, roof glazing may allow sun into a space when the north wall is shaded
  • the owners lifestyle – when do they like to be in the sun (or shade).
  • the location of thermal mass within the proposed building (see passive design)
  • the provision of natural daylighting to building spaces (see daylighting)
  • views
  • the location of outdoor spaces.

Sun paths

The best way to assess the passage of sun across a site is to use sun path diagrams or models (see below). A site visit may help to identify site-specific conditions such as the impact of a particular tree or distant ridgeline.

‘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). The maximum altitude of the sun at any selected place in the southern hemisphere occurs at solar noon around December 22.

Sun's altitude


Azimuth (sometimes known as bearing) is the direction of the sun as shown on a compass. For sun bearings at sunrise and sunset at different New Zealand latitudes, see Land Information NZ’s astronomical information web page.

Sun path diagrams and modelling

Sun-path diagrams and computer models can be used to assess the impact of the sun on a building site. It’s also important to consider the impact of obstructions such as trees, buildings and landforms – either nearby or towards the horizon. They can also be used to determine shadows cast by the proposed building

These are more useful once you have a sketch design and accurate contour plans to work with.

Victoria University’s Centre for Building Performance and Research has a web page showing sun path diagrams for New Zealand locations. In these diagrams, the outer circle represents the horizon, and the centre is the point of observation. The diagram shows the altitude of the sun at different times of day. The diagrams use clock times (12 hours ahead of GMT), as opposed to solar times. They are reasonably accurate for places within about 1 degree north or south of the allotted latitudes.

You can achieve more detailed sun path modelling using 3D computer programs such as Google SketchUp or publications such as Sunshine and shade in Australasia or Designing for the sun.

Obstructions

When you’re considering sunlight and building design, consider the future as well as the present. A small tree on a neighbouring site may grow into a large one that blocks the sun, or a building may be put up on a site that is currently vacant, or an existing building demolished and a larger one erected.

Sometimes there may be some conflict between retaining existing trees on site and/or local council tree preservation requirements and getting enough sunlight onto the site. It may be beneficial to retain a tree for summer shade.

Difficult sites

It may be more difficult to take advantage of direct sunlight on some sites – for example, sloping sites at the bottom of the hill that faces south or within a valley. However, some of these difficulties can be overcome with good design to ensure the building is warm and healthy (see passive design).

Solar radiation

Solar radiation is the amount of energy a location gets from the sun. The amount of solar radiation that can be used in passive heating design depends on the latitude and sunlight hours received at the site. For buildings in low solar radiation localities window area and the amount of thermal mass provided will need to be greater to maximize benefits of passive heating design. 

When designing solar panels or photovoltaic panels, solar radiation data for typical reference years can be bought through the Sustainable Electricity Association NZ website, or the NZ Photovoltaic Association website. Information is available for Kaitaia, Auckland, Gisborne, Levin, Paraparaumu, Christchurch and Invercargill.

Radiation information is also available from NIWA and from the Energy Efficiency and Conservation Authority’s Solar Water Heating Guidebook: A Technical Guide for Building Professionals  (PDF, 1.35MB) which contains information about compliance with proposed New Zealand Standards on solar water heating.

Ultraviolet radiation

Levels of ultraviolet (UV) radiation on a site may affect the durability of materials over a building’s lifetime. Changes in UV levels from summer to winter might also influence passive design decisions.

NIWA advice is that the intensities of summertime UV in New Zealand will remain high compared to many other countries.

The National Institute of Water and Atmospheric Research has a UV Atlas tool which provides information about UV levels around New Zealand for the period since 1960. It can be downloaded from NIWA’s UV Atlas web page. Specify materials that are more resistant to UV degradation (such as fading) when the index number is higher.

Finding information

General climate data

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, mean temperatures and more. The NIWA website also has a free climate overview, and NIWA can provide site-specific information on enquiry or using its Climate Explorer web tool. Climate information is also available from the MetService website and some limited rainfall information is in E1/AS1 Surface water.

Climate information is also available from the MetService website.

Aerial/satellite images

Aerial photographs give an indication of neighbouring buildings and vegetation. You can obtain aerial images through:

You can also ask your local council for plans of neighbouring buildings (some councils provide this information online), and have a survey done on site to indicate neighbouring levels.

For your clients

To help your clients understand building orientation and sun paths, refer them to www.smarterhomes.org.nz/design/orientation.

To help them understand the impact of climate on design, refer them to www.smarterhomes.org.nz/siting-landscaping/climate.