Buildings are a major source of environmental impacts. In addition to local impacts, considerable amounts of energy are:

• consumed in operating buildings

• embodied in the materials used in to make them.

In all buildings accounts for as much as 40 proportion of Australia's greenhouse gas emission.

In an effort to control energy consumption in buildings, recent amendments to the Building Code of Australia (BCA) included a Performance Objective for residential buildings of reducing greenhouse gas emissions by efficiently using energy.

All new construction must rate above a particular level of thermal performance when modelled in an accredited simulation program or comply with specified (deemed-to-satisfy) construction provisions. The BCA currently requires a 5 Star rating. Some states have adopted this performance level while others have currently deferred its adoption.

Lightweight timber framed solutions meet 4 Star requirements relatively easily but can need considerable and often expensive modifications to achieve a 5 Star rating in cooler climates. As it is perceived to be easier to achieve a 5 Star rating in the simulation programs with a concrete slab floor, timber subfloors are loosing market share. This is notwithstanding the other construction and environmental benefits using a lightweight floor may bring to a project.

The 5 Star thermal performance project is testing the science behind building and rating the ‘energy efficient’ homes of the future. The project has two components that test the actual thermal performance of lightweight timber framed solutions. These are:

• the thermal performance test cells at the University of Tasmania's Launceston Campus. You can find out more about the test cells here (ref to test cell site)

• the 5 Star test houses being established in Hobart in association with prominent Hobart building company, Wilson Homes.

The test houses, currently under construction, will be:

• A Compact 5 Star Timber House – a compact, affordable but well detailed house that includes a timber framed floor and achieves at least a 5 Star rating when assessed under AccuRate.

• A Compact 5 Star Timber Frame and Concrete Slab House –a house with an orientation and general building fabric identical to the 5 Star Timber House, that achieves at least a five star rating and has a standard concrete slab on ground.

• A Compact 4 Star Timber House – a compact, affordable but well detailed house that includes a timber framed floor and achieves a 4 Star rating when assessed under AccuRate.

To ensure results are directly comparable between the buildings, the orientation and floor plan of the three houses will be identical. Except for the inclusion of the slab, the external fabric of the two five star houses will also be identical. The external fabric of the 4 Star house will be similar but necessarily altered to achieve this rating.

The thermal performance of each house will monitored by an extensive sensor array recording temperature, humidity, air movement, solar radiation and electricity use. The houses will be monitored empty (in a free-running state) for three months in winter and for a further two winter cycles occupied. You can find out about the monitoring here (ref)

The information gathered will be used to assess the accuracy of methods used to determine the ‘energy efficiency’ of Australia's housing. This includes an evaluation of the CSIRO’s AccuRate thermal performance modeling program, soon to be a key thermal calculation method for the Building Code of Australia.

The specific research objectives of the project are to:

• validate the AccuRate software in a full building

• compare the thermal performance of a building with a timber framed floor with  that of a building with a concrete slab on ground floor

• measure the thermal performance of a range of timber assemblies individually and as systems.

To ensure that the results of the research are integrated into the national building design and regulatory communities, other building researchers will be invited to cooperate with the research and its progress will be reported through a broad communication program.