Minimum energy efficiency standards for new housing are typically informed by regulatory impact statements, underpinned by lifecycle costing (LCC) analysis. While LCC techniques are empirical and testable, such analysis is informed by considerable assumptions on key parameters. These assumptions are often heavily contested in the literature and by built environment stakeholders, but there is limited exploration of their implications within wider policy developments. This paper addresses this gap by analysing the impact of a number of assumptions and their implications within a LCC analysis of zero energy housing options in Victoria, Australia. The results show that changes to assumptions on key parameters have significant impact on LCC outcomes, with associated policy implications. Analysis shows that there is a requirement for a detailed review and debate of the assumptions applied within LCC analysis which is used to inform the development of minimum energy efficiency standards in Australia and internationally. In particular, as housing is a long-lived infrastructure, the issue regarding the use of assumptions based upon historical data or data based upon future predictions is critical to the development of policy and energy efficiency standards. (C) 2014 Elsevier B.V. All rights reserved.