Alterations and Additions – DTS or NatHERS?

So you’re working on an Alterations and Additions project, and you need to include an energy report for the RBS. When it comes to National Construction Code (NCC) compliance for your building designs, how do you know if you should get a DtS report or a NatHERS assessment done? Let’s break it down!

First off, what are we talking about?
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A DtS (Deemed-to-Satisfy) report is a comprehensive rundown of how your building design meets the energy efficiency requirements outlined in the NCC. It’s a detailed analysis that covers every aspect of the design, from insulation to shading, and sets out specific measures and strategies for achieving compliance. One of the hallmarks of a DtS report is that it looks at each aspect individually – walls, ceilings, windows, etc. are all assessed separately.

On the other hand, a NatHERS (Nationwide House Energy Rating Scheme) assessment looks at the dwelling as a whole, with construction aspects able to interact and offset individual performance results. This can mean that a poorly performing aspect – for example, windows – can be bolstered by above-average performance elsewhere – such as roof insulation. NatHERS software models the thermal performance of your building design and gives it a star rating from 0 to 10, with 10 being the most energy efficient. This provides a quick and easy way for your clients to understand the energy efficiency of their home and compare it to other design options.

But that’s the simple, new build rundown. Things get a little more complicated when it comes to Alterations and Additions projects…

For a renovation, the NatHERS star rating requirement is reduced. Rather than needing to achieve the state minimum – soon to be 7 stars in Victoria – a formula is used to generate a dwelling-specific minimum star rating. The formula uses the retained volume percentage and thermal performance of the existing dwelling in comparison to the volume of altered/new works and their thermal performance to calculate a reduced total star rating requirement. In order to complete this formula, two NatHERS assessments need to be completed; one for the original, existing dwelling, and one showing the planned works.

A DtS report for a renovation looks very similar to the report for a new build, with one notable difference – an Alterations and Additions report allows for the existing construction elements to be excluded from complying with the requirements. This means that, depending on the extent of the alterations, only new work needs to meet DtS requirements. As such, retained walls, ceilings, and floors don’t need to be retroactively insulated, and retained windows don’t need to be replaced.

So what’s better for your project?

While a NatHERS assessment still allows for individual construction aspects to be offset by each other, the fact that the existing dwelling needs to be included in the assessment may mean that even meeting a lower star rating will require insulation installation to retained areas. On the flip side, while a DtS report is likely to exclude the retained areas of the dwelling, the fact that each aspect individually must meet DtS requirements can mean that if a certain construction element isn’t performing well, it can’t be offset by the good performance of another aspect.

As per usual, both options have their pros and cons, and it’s best to make the decision on which pathway to choose on a case-by-case basis. But that’s what we’re here for – rest assured that we have experience with both options and are more than happy to help you make the best decision for your project! So feel free to reach out about your Alterations and Additions project, and we’ll sort it out together!