Abstract: Planning legislation across Australia explicitly aims to improve the environmental efficiency of the built environment through better design. Likewise, development industry associations also advocate for better environmental outcomes. Yet these objectives are often only achieved on signature projects while the majority of suburban development continues to produce increasingly unsustainable outcomes. This paper reports on a study of a suburb in Canberra that has experienced significant redevelopment of houses in the last eight years. It finds that, despite the majority planners, architects, building designers and residents expressing a desire to achieve a more environmentally efficient outcome, very few houses achieved this ambition. A sample of n219 development applications submitted between 2003 and 2006 show an average gross floor area of 295 square metres. The research also reveals that these new homes have an average of 2.4 occupants and this equates to over 120 square metres of floor area per occupant. Commonly known as the McMansion effect, this study finds that the majority of built environment professionals and residents are critical of such surplus construction and yet little is known about why such development occurs. These findings form part of a PhD examining the McMansion effect. It finds that no clear environmental objective exist for suburbs undergoing renewal. As a result, many decisions are made that culminate in an outcome residents find both unsatisfactory and undesirable. It argues that planning legislation can do a lot to curb such developments in suburbs undergoing renewal without undermining the community’s right to redevelop.