Fears that houses with suspended timber floors cannot achieve a 5-star rating under the latest Australian national and state regulations for thermal comfort have been diminished (completely dispelled might be a bit strong for our constituency), reports senior editor Jim Bowden in this flashback story to July 2007.
Studies by the Insulation Council of Australia and New Zealand (ICANZ) and the Forest and Wood Products Research and Development Corporation (FWPRDC) have confirmed that, with very limited changes, suspended timber floor construction can easily exceed a 5-star rating.
Commissioned independently by FWPRDC and ICANZ, both studies provide homeowners, building designers, and builders with a selection of simple, cost-effective options to improve the energy efficiency of their homes.
Trevor Lee, director of buildings with Energy Partners and one of the FWPRDC report’s authors, says the study identified 10 top techniques for improving the calculated efficiency rating for suspended timber floor houses across hot, temperate, and cool climates.
The preconception of numerous builders, energy raters and general consumers that dwellings with suspended timber floors could not simply and cost-effectively achieve a 5-star energy rating have been dispelled by the Energy Partners report.
“In all climates, the two most effective techniques alone were sufficient to increase the rating by more than a star,” says Lee.
“Various techniques will be more suited to warmer or colder climates. But ceiling and wall insulation are always important in all climates for achieving a high star rating,” he said.
ICANZ president Dennis D’Arcy says it is as simple as making smarter use of existing low-cost options, such as increasing wall and ceiling insulation, installing ceiling fans, better glazing and draft proofing.
“The 5-Star Building Code of Australia and the NSW BASIX energy efficiency provisions can easily and cost-effectively be achieved,” he said.
The two reports also independently support Bernard Hocking’s in-field experience as a technical consultant for the Association of Building Sustainability Assessors (ABSA), who says, “Timber, plus smart design and the right insulation in the right place, makes achieving 5-Star and BASIX easy.”
In May 2006, the Building Code of Australia (BCA) raised the energy-efficiency requirements for all new houses to the 5-star standard. At the time, the Australian timber industry protested that the BCA had over-emphasised increasing thermal mass in house design, materials and construction as the primary means of reducing greenhouse gas emissions. There was widespread belief that timber was not getting a fair go.
That was supported by a Productivity Commission report on energy efficiency, saying, “The commission is concerned that the analytical basis for these regulations [computer simulations of energy loads within buildings in each climate code] may be flawed”.
The AccuRate software used to determine 5-Star rating in Australia was developed using a ‘thermal mass’ philosophy. But timber frame construction is generally lightweight and thus penalised in terms of its performance and the maximum rating score that can be achieved.
Greg Nolan, associate professor at the Timber Research Unit, School of Architecture University of Tasmania (UTA), says the system is not deliberately unfair if you only look at operational heating and cooling.
“However, if you look at the whole energy picture, the low embodied energy of timber is not recognised,” Nolan said.
“Also, the dominant view of those involved for many years in thermal performance issues has been that the high mass house is good. This is true if conditions are good, but not the case once you lose a predominantly north orientation.
“So, one might observe that the benchmark has been pegged so that a slab house is generally just acceptable, and its timber floor equivalent is generally just not acceptable.”
Nolan says there are also factors that could improve the thermal performance of timber, and all other houses, that don’t get much attention in the regulations – like air infiltration.
Nolan believes the AccuRate computer model is very sophisticated for what it does but notes that there are some big assumptions. “The stated aim of the BCA is to reduce greenhouse gas emissions by using energy efficiently. But the only types of energy considered when designing housing are heating and cooling energy, modeled to maintain an assumed level of thermal comfort.
“There is no guarantee that people actually operate the building this way, or that heating and cooling are the main forms of energy use. Other types of energy use, such as the energy embodied in the materials and the energy to run appliances, get little or no attention.
“And as The Age reported recently, in Victoria energy usage for new 5-Star houses is actually on average far in excess of older houses – all because people have bigger homes, more downlights and other high-energy gizmos.”
Nolan also questions the veracity of the 5-Star process, particularly as the things that have to be done during construction to meet the requirements are not actually inspected!
“Also, there has been very little testing against Australian construction practice. This means that things can be happening on the building site that negate many of the things that the regulations originally intended. Combine that with no inspections and you can see that the regulations mean well but can’t be guaranteed to deliver on their intent.”
Nolan’s suggestions to building designers looking to improve thermal efficiency of Australian houses in cool and cold climates include:
• Adequately and correctly install insulation.
• Wrap the building and tape all joints.
• Fill gaps around windows, doors and sub floor openings.
• Use double glazed timber windows.
• Put living spaces on the sunny side.
• Provide eaves and other devices to shade windows that get too much summer sun.
Editor’s note paradigmatic error: A recent study House Energy Rating Systems (HERS) by a group at the University of Adelaide School of Architecture, Landscape Architecture and Urban Design concluded that there was little indication HERS worldwide were based on robust evidence. In fact, a likely source of paradigmatic error can be recognised in all HERS. Rather than producing policy framings on the basis of actual energy consumption, as recorded in ‘real’ households, policy makers and their advisers have focused on specifying the physical properties of construction, informed by data developed by simulation, with the building theoretically emptied of [its] unruly occupants and replaced by model ‘visual’ inhabitants.
“The differences between theoretical results and the real outcomes ‘out there’ if detected are attributed almost entirely, with negligible evidence, to the ‘rebounds’ effects,” say the authors Terry Williamson, Veronica Soebarto, Helen Bennetts and Antony Radford.
“Research by social scientists looking at this issue tells us, not surprisingly, that the difference most likely lies in the fact that houses are inhabited and controlled by real [not virtual] people”, the authors assert.
Meanwhile, the Royal Australian Institute of Architects has called for more government action and incentives to cut energy emissions – particularly in existing buildings.
“Improving energy efficiency in new buildings, particularly new homes, doesn’t always require advanced and expensive high-tech solutions,” says RAIA national president Alec Tzannes.
“Smart design such as sun shading and natural ventilation, better insulation and using recycled building materials can help make a difference, and still allow us to maintain a high quality of comfort.”
A more pressing challenge, he says, is to achieve energy efficiency in existing buildings, where targets and incentives to accelerate refurbishment were needed.
