The issue with South facing obstructions in NatHERS Technical Note 1
Part 5 of NatHERS Technical Note 1 states that an assessor should not model “highrise/topographical features that are located at the midpoint between SSE and S and finishes at the midpoint between S and SSW”. In layman’s terms, don’t model obstructions to the South.
However, 5.1.2 states that “where a feature is outside the limits set by Clause 5.1 but because of topography it may still cause a sun obstruction – it must be modelled”
Clause 5.1.3 also states that “The features noted in clause 5.1 may sometimes impact on a dwelling depending on the topography, building site levels and the siting of the dwelling. In these instances assessor judgement is required”
The last sentence being “assessor judgment is required” is cause for concern. How as an energy assessor can you make a judgement on the effect of South facing obstructions unless you have modelled them and came to the conclusion that they have no significant impact on the rating? You can’t!
What would you call a significant impact?
One would assume any change in the MJ/m2 would be an impact however is that significant enough to warrant no South facing obstructions to be modelled? In my opinion if the rating changed by 0.1 Stars then that would be significant, that change would cause the insulation and glazing specification to reduce or increase in order to compensate.
If you are an energy assessor and claim your ‘assessor judgement’ has lead you to the conclusion that south facing obstructions have made no impact on your assessment yet have not modelled the south facing obstructions then your report is incorrect. You cannot prove ‘little impact’ as you have not analysed the data.
I question any report with no South facing obstructions modelled for two distinct reasons.
Firstly, if you modelled South facing obstructions and they did not deviate the report by more than 0.1 Stars why would you then go to the effort to delete the extra work involved in the additional modelling? Have you also supplied sufficient data to prove that the South facing obstructions made no impact?
Secondly, after completing tens of thousands of reports I am still yet to see a report where South facing fences or buildings have not made some impact on the report data, unless it is modelled you will never know. Our company has seen shifts in ratings up to 0.5 Stars just from South facing obstructions alone. This is not extra work it is simply producing data that is accurate to NatHERS protocols.
Technical Note 1 Section 5 should be re-written stating that all South Facing obstructions be modelled, given the unlikely event those obstruction make no significant difference to the result they still have to be modelled for an assessor to make a judgement call. Why remove them after the fact.
How as a building surveyor or someone reading a Universal Certificate know if an energy report has South facing obstructions included?
Simply put, you can’t. Nowhere on the Universal Certificate does it state South Facing obstructions, in fact the certificate does not state any obstructions. Your faith has been placed solely on the competence and accuracy of the energy rater in the hope they have entered the data accurately.
If you were unethical and wanted to cheat the system this is a perfect way to potentially gain an additional Star on an energy report without anyone realizing.
Short of reviewing a copy of the data file no one would know if all South facing or in fact ALL obstructions had been deleted or not modelled.
There is talk of mandatory disclosure being introduced into the 2021 NCC, should this happen and a review of energy efficiency reports is requested this type of data manipulation or inaccuracy will certainly cause issues. You should always have your reports completed by an ethical company that follows all codes and current protocols.
If you have any questions about this topic or any other please call one of our consultants on 1300 033 343.
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