The Building Regulations Blog

The staff at BDC have many stories about their BCA Section J variation experiences. One of the common threads is the detailed questions about a specific Section J variation. You know the ones like:- what if the R value exceeds the DTS R value?

The Building Regulations Blog suspect the reality for most building surveyors (there are some exceptions!) will be that the ESD and Mechanical Services designers will be way ahead on their knowledge of the detail in this area of the design. But the key starting points for any discussion about alternate designs is:

1. What is the assessment method going to be? and
2. What are the acceptance criteria for the “sign off” of the alternate design?

For an alternative design the strategies for these may include:

1. Modelling of the building for energy consumption against the DTS reference building; or
2. Comparing a varied DTS design against the DTS benchmark; or
3. Some other assessment method that establishes a benchmark for compliance with the subjective performance requirements.

The assessment method is not so hard to choose. Choosing the benchmark and trying to quantify any acceptance criteria gets harder. OK its easy for the JV3 verification method i.e. comparing the energy consumption for the alternative design against the energy consumption for the DTS reference building.

But the further the design team moves from strategy 1 to 3 above the harder it gets for both the design team and the building surveyor. The sketch below illustrates the issues for the 2nd strategy and tries to highlight the difficulty with managing the implications of variations to the DTS details for energy efficiency.

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