28 June 2012 – Energy consultancy Sustainability House recently surveyed 12 of the country’s high volume residential home builders on behalf of the federal Department of Climate Change to see if the cost of achieving six stars in new housing could be reduced through design.

The study, which included AV Jennings, Stockland and Meriton found that modifying a home’s design to suit the climate and orientation, rather than increasing building specifications such as insulation levels, could achieve six star energy efficiency standards with reduced construction cost in all buildings in all climates.

The work was part of the government’s inquiry into how to whether to harmonise rating tools and other energy efficiency options, surveyed in  National Building Energy Standard-Setting, Assessment and Rating Framework

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Among the findings by Sustainability House new home buyers focused on affordability are making it harder for builders to meet energy efficiency standards in dwellings, a new study highlights.

The consultancy found buyers had a perception that energy efficiency involved extra costs even though good house designs could actually reduce costs.

The study found those perceived extra costs were a hindrance to stringency around energy efficiency compliance. And home builders participating in the study were concerned there was little or no auditing to ensure efficiency standards in new homes had actually been met.

Some believed if energy efficiency standards were introduced when land was sub-divided rather than at the design stage or later, it would be easier to achieve six star energy ratings for new homes in a cost-effective manner.

They said poor positioning –  the orientation of a dwelling – particularly the location of the living area – during sub-division locked in impediments to achieving those standards cost-effectively, resulting in redesigns being done later at extra expense.

For the study, the federal government’s Department of Climate Change, contracted energy efficiency modeller and adviser, Sustainability House to determine to what extent the cost of achieving six stars in typical new residential buildings could be reduced through changing the design of buildings while still maintaining their features, functionality and size, before upgrading specifications.

Sustainability House asked 12 of the country’s high volume residential home builders for their input, using 20 home designs with builder supplied specifications in eight capital cities and a sampling of best, worst and intermediate orientations.

Designs were sourced for a range of dwelling types, from single and double storey detached and semi-detached homes to apartments.

A quarter of the study participants said they considered the energy efficiencies for their properties at the design stage while the rest considered them later on.

Sustainability House also surveyed the companies that provided plans for the study, to better understand the efficiency and cost issues faced by residential builders.

While the study’s focus was on cost-effective housing redesign options to achieve energy efficiencies it did not consider the most energy-efficient changes independent of cost.

Each of the state’s capital cities were designated by the climate types they represented with the Northern Territory capital Darwin zoned hot; Brisbane, Perth, Sydney and Adelaide, temperate; and Melbourne and Hobart, cold.

Modifying a home’s design to suit the climate and orientation…
could achieve six star energy efficiency standards

The study found that modifying a home’s design to suit the climate and orientation, rather than increasing building specifications such as insulation levels, could achieve six star energy efficiency standards with reduced construction cost in all buildings in all climates.

Builders in the study said when they focused on climate and orientation in their portfolio they were able to increase energy efficiencies in redesigns by an average one star, and decrease construction costs by nearly 1.6 per cent, compared to the original design.

The 2009 Council of Australian Governments National Partnership Agreement of Energy Efficiencies effectively increased the minimum acceptable standard for residential buildings from five to six stars. The changes were introduced to the Building Code of Australia in May 2010, along with minimum performance standards for lighting, hot water generation and other measures.

Most new Australian homes are
designed to achieve average results
rather than
optimal energy efficiency performance

Sustainability House says most new Australian homes are designed to achieve average results rather than optimal energy efficiency performance.

The study pointed to a range of climate-dependent, no-net cost changes for improving thermal performance, such as:

  • optimising roof and external cladding colours
  • considering window size and aspect
  • moving window glazing from east/west to north/south orientations
  • mirroring the building (reversing the design) using polystyrene core floor slabs
  • addressing shading

“By investing some efforts in tailoring designs to suit different orientations and climatic conditions, construction costs could be reduced to allow residential builders to offer a more affordable product in a market where cost is the bottom line,” said Sustainability House.

The traditional approach of estimating the cost impact of increases in residential building efficiency standards was done by increasing the specification of a design until the required energy efficiency benchmark was reached.

Sustainability House said this method could overestimate the impact on the cost of the building.

How about some education?

Builders surveyed felt home buyers generally had a poor understanding of efficiency regulations. They suggested a government education program for home builders and their staff to learn how to give the right information to home owners to alleviate the problem.

Another option was to give home owners a user manual with energy saving tips and methods, like those given to commercial buildings owners.

An education program was also suggested for local councils because anecdotal evidence had been found of conflicts councils had with the energy efficiency regulations.

Other conflicts builders identified included air-tightness causing condensation issues and difficulties achieving six stars for houses built on slopes with raised sub-floors.

As only 28 individuals in the construction industry responded to the additional survey it did not constitute a statistically valid sample of residential builders, but those that did respond represented some of the largest residential construction companies in Australia.

Most said they did not have home
or apartment designs that could meet ratings
higher than six stars because
home buyers were primarily interested in cost,
not energy efficiency.

Most said they did not have home or apartment designs that could meet ratings higher than six stars because home buyers were primarily interested in cost, not energy efficiency.

Glazing was highlighted as one of the most important factors contributing to thermal performance. Windows cost less to insulate than walls and ceilings so it is a cheaper value proposition.

As airconditioning was in all aspects of people’s lives they had an expectation of controlling the temperature of the environment at all times, said the builders.

This had resulted in dwelling designs isolated from the climate they were in, leading to insulated buildings, but conversely, insulation could enhance the positive aspect of a building’s location such, be it winter heating from the sun or blocking the sun to keep a building cool.

Other key survey findings included:

  • Quantity surveyors tended to overestimate costs for redesigns by 30 per cent or more
  • Decreasing window size to achieve energy costs savings could make homes less attractive and decrease sales but buildings could achieve the six star requirement without substantial loss of glazing area
  • Volume building designs, such as apartment blocks, had the potential to be energy efficient at a lower cost that presently incurred by builders. Putting windows right round the building led to average performance in all orientations
  • The location of living areas in homes to optimise views, desires of the home owner and functionality were factors be considered besides energy efficiencies
  • Reducing construction costs might cause cost increases elsewhere
  • Project home builders preferred to have designs that could be used in any orientation yet different orientations and good design principles could result in cost savings
  • Double storey buildings achieved the lowest average star rating using original designs
  • Apartments positioned on the corner of the building rated the highest stars, using original designs
  • * Hobart achieved the highest average star rating and Brisbane, the lowest, using original designs
  • Builders said presently the construction cost of increased a star rating from five to six was on average $3500

Builders and their franchises participating in the survey were:

  • AV Jennings Developments
  • BGC Residential
  • Cavalier Homes
  • Devine Homes
  • Dixon Homes
  • GJ Gardner Homes
  • Hotondo Homes
  • JWH Group
  • Meriton
  • Metricon
  • Rossdale Homes
  • Stockland
  • Weeks Group