Alterations and Additions: Extension Glazing

Created by Vicki Marshall, Modified on Fri, 9 Dec, 2022 at 8:59 AM by Vicki Marshall

Region: Victoria

Assessor Question:

I am currently doing an extension energy rating in Firstrate5 of the attached plans. Regarding the VBA practice note EE-04 in relation to the external glazing been uniform to the proposed glazing to the whole storey, am I able to nominate the existing windows which are already comfort plus glazing with higher performance on the Northern windows of the existing house, but then only have clear glazing performance figures for the 3 new windows of the extension so the glass will match the existing windows on the South side of the house?
Or will I have to rate all of the windows to the same performance of the new windows as clear glazed?

TechLink Response:

  • It is acceptable to include the actual performance values of all existing and new windows in a NatHERS rating of an alterations and additions project.
  • The resulting score will then be the real/exact result that the dwelling will achieve after the construction is completed.
  • This provides a totally transparent understanding for all concerned as to the building fabric energy efficiency that can be anticipated.
  • The procedure outlined in the VBA Practice Note EE-04 provides a pathway to assess compliance of the new construction in the circumstance where existing widows are providing an inferior level of performance as compared to the specification of those nominated for the proposed works but are deemed unreasonable to warrant replacement on an overall cost benefit to energy efficiency balance.

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