The performance requirements of our Australian National Construction Code (NCC) require us to achieve stated objectives ‘to the degree necessary.’ The NCC then prescribes measures under the Deemed to Satisfy (DtS) provisions to meet these requirements.
I was recently talking to a colleague about this vague term used in the NCC ‘to the degree necessary.’ The question arose, do the Deemed to Satisfy measures actually achieve a result ‘to the degree necessary?
In many cases the answer is, NO.
Our particular discussion was about sub-floor ventilation in relation to condensation, moisture & mould. The NCC sub-floor requirements are deficient in this regard, in part due to the separate and disconnected DtS provisions for sub-floor ventilation and energy efficiency. The DtS energy provision requirement decreases energy flow for energy savings, but this also leads to a decreased drying capacity which renders the DtS ventilation provision inadequate.
The only way to achieve a result ‘to the degree necessary’ is to recognise the knock-on effects and interrelation of code-based guidance measures, and to treat the building as a system.
When a Deemed to Satisfy provision does not achieve a result ‘to the degree necessary’ we can create a Performance Solution, (which needs to comply with the Performance Requirements ‘to the degree necessary’). A Performance Solution requires a Performance Based Design Brief (PBDB) which needs to be developed in consultation with all relevant stakeholders.
A problem that arises with Performance Solutions is that a major stakeholder in a PBDB is the Relevant Building Surveyor (RBS). More often than not, the RBS has not been appointed at building design stage. This makes it hard to achieve a result ‘to the degree necessary’ given that all stakeholders are not available…it actually makes it impossible.
You can, however, achieve compliance by just applying the DtS provisions. The problem here is that Performance is not achieved thereby not achieving a result ‘to the degree necessary.’ This gets a bit treacherous, especially for the RBS, when the BCA explicitly states that it accepts no liability for any problems arising from following its guidance.
Excertp below from a post by architectural scientist, Tim Law:
The BCA sets the minimum required level for the safety, disclaims fitness for purposes and accepts no liability for negligence. The building legislation, on the other hand, requires fitness for purpose as a minimum, and entrusts the building surveyor with that duty of care to the building owners and to the public.
In many cases, Compliance does not equal Performance. The trick is to achieve both performance and compliance at the same time; not an impossible task but one that is becoming increasingly difficult within our current code.
The procedure is to find something that works, then find a way for it to comply.
Click here to read Tim Law’s discussion titled, ‘DtS Compliant, but unfit for Purpose’.