The era of legislation and creditable methods towards the production of sustainable building are upon us. Everywhere we look, the desires and intentions for 'greener' building design and operation are evident. In part, this response is due to the Australian government and other independent organisations that have developed policy on rating tools and performance ranking measures, all with the intensions of obtaining environmentally sustainable buildings.

We are implementing design guidelines and best practices to our buildings. We are also attempting to investigate 'by design' vs. 'as built' performance. Yet, with due respect to all of these courageous efforts and good intentions, one needs to ask whether the end product is genuinely performing as planned. It would appear that what we really want to obtain is an evidence-based 'as performing' assessment.

With rating systems endorsing innovative environmental design solutions it could be asked: Are our buildings really operating as rated? Do we know whether our designs are in compliance with what was calculated or simulated? Is there a feedback loop informing the design process on successes or failures?

The Mobile Architecture and Built Environment Laboratory (MABEL) was conceived upon the principle of investigating building environmental performance in situ. MABEL provides the first means of integrated, on-site measurement of the key aspects of internal built environments; energy, lighting, air quality, ventilation, acoustics and comfort using state-of-the-art technology and instrumentation.

The intention of this paper is to explain the how and what need to be measured in our buildings if we are to search of a genuine performance answer as well as the information to provide a solution. Several results of real building measurement are provided here, suggesting that a national program on 'as performing' is required if we are to proceed in a sustainable manner.