This report is the Interim Technical Report for the Building Code Energy Performance Trajectory Project. It accompanies the Interim Synthesis Report for the Building Code Energy Performance Trajectory Project, entitled The Bottom Line – the household impacts of delaying improved energy requirements in the Building Code and which was published on the 8th of February 2018, providing more detail on the assumptions behind and the preliminary results from the underlying modelling work.

The report provides the following key items:

• Background, context and methodology for the study.
• Review of parameters used in the economic assessment.
• Preliminary baseline results for residential building energy modelling.
• Preliminary benefit costs analyses for potential residential construction upgrades.
• Preliminary modelling results for residential building energy modelling, incorporating improvements that are currently cost-beneficial.
• Assumptions for the non-residential (commercial) building energy modelling.
• Preliminary stock model projections of the impact of proposed residential upgrades at state, territory and national levels.

This study assessed a range of simple energy efficiency opportunities across three building types (detached, attached and apartment), and three climate zones covering Australia’s largest population centres. It sought to identify improved energy efficiency measures for which the capital cost is outweighed by financial benefits ('cost-effective') from a societal perspective over the lifetime of the relevant building elements, in most cases a 10-15 year period.

It considered opportunities to improve efficiency of the building ‘fabric’ (walls, ceilings, windows etc.) and fixed equipment (hot water, lighting), but not plug-in appliances, which are regulated separately. Results presented in this report are preliminary, and a number of improvement opportunities remain under investigation.

The analysis used conservative assumptions and focused on simple lowest common denominator opportunities to improve energy efficiency.

Importantly, the analysis did not consider opportunities for accelerated adoption of best practice building design for energy efficiency, such as optimal building orientation and window sizing and placement.

Preliminary findings in relation to the residential study are as follows:

• Improved air tightness, ceiling fans and roof insulation were the most cost-effective measures identified, with variations across the different building types and climate zones. Of the cost- effective improvements, measures to reduce infiltration are the most significant building ‘fabric’ measure.
• Combined, these cost-effective measures could reduce energy consumption for heating and cooling by an estimated 28 to 51 per cent across a range of housing types and climates. This is equivalent to between 1 and 2.5 Stars on the NatHERS scheme.
• A high-level analysis of solar photovoltaics (PV) suggests that it is now highly economic. For buildings where solar access is available, PV is economic to the point that 60-70% of the generated energy is being exported under today’s economics. However, it should be noted that PV does not of itself deliver a range of other co-benefits provided by the other energy efficiency measures modelled in this study, such as comfort, health and resilience, and faces a number of implementation challenges.
• Lighting and domestic hot water have potential for cost-effective upgrade in the mid-term, but is not immediately cost- effective on the economic analysis used for this study.