How do I achieve acceptance with an RBS for an energy rating for an extension to an existing dwelling?

  • DTS Extension,
  • FirstRate5
  • Victoria
Last Updated: February 20, 2020


I am in discussion with an RBS regarding acceptance of an energy rating report for an extension. The proposed extension exceeds 50% of the original dwelling floor area and volume and has been rejected by the RBS.

I understand that in these circumstances approval can not be granted on the volume calculation formula alone, and that additional evidence is required to allow partial compliance which was provided in our report. As we have used this report format in the past which has been acceptable to other RBS, could you please advise if there has been a change in the regulations or the required method of assessment?

In addition I would also like to know if a NatHERS assessment is classed as a ‘Performance Assessment Report’ as requested by the RBS, and what is the position if the project were assessed under DtS and produced a ‘Fail’ condition in the Glazing Calculations Table.



The clear understanding is that the logic of the adjustment formula means that is can be used for all alterations and additions projects to take into account the under-performance of the existing portions that are deemed unreasonable to upgrade on a cost benefit basis.

NatHERS Ratings are one of the two Deemed to Satisfy pathways for demonstrating compliance of building fabric thermal performance. The other being Elemental DtS.

Unfortunately the issue you have raised is a known to both Design Matters and the VBA, however it requires the VBA to provide clarification ultimately – something we have been pushing for repeatedly.

It is likely that the only way to overcome this particular enquiry as it currently stands would be to have someone at the VBA advise the RBS that the adjustment formula is suitable for this project. You may wish to head down the DtS path in this instance.