by Vicki Marshall, DMN Senior Sustainability and Thermal Performance Manager

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Shining a light on Shading...

And why it matters in the scheme of building design and thermal performance assessment.

By Vicki Marshall, DMN Senior Sustainability and Thermal Performance Manager

As revealed in quality assurance data over a number of years, shading is one element that consistently features in the list of most common errors in NatHERS Modelling.

It’s true that modelling shading sounds simple enough, however it is a complex component of the NatHERS energy efficiency assessment, with many elements and variables to be considered… and the issue does not discriminate. Whether Performance Assessors have been accredited since 2010 or 2021, the shading conundrum is present and consistent across all softwares.

So why is shading such a big deal I hear you ask?

According to the NatHERS Assessor Handbook, not only can shading make the difference between a dwelling being comfortable or uncomfortable to live in, it can also have a significant impact, either positive or negative on the thermal performance reflected in the NatHERS star rating.

Whether by oversight or intention, omitting or incorrectly modelling shading can artificially improve star ratings, leading to unreliable and misleading information for regulators and home owners alike.

As a result, heating and cooling loads and projected energy consumption of the home can be significantly skewed... thus we end up with a NatHERS Certificate that provides misleading information, a home that generally speaking underperforms and has higher ongoing operating costs over its lifetime for the occupants. For example, the shade cast onto a dwelling can limit the amount of sun or solar radiation striking a building, thus affect the ambient temperature inside the dwelling. While large shadows can be beneficial during the summer months, the reverse is true during winter months and in cooler climates where smaller shadowing and higher solar gain can be beneficial and these factors must be correctly entered into the NatHERS modelling software to obtain accurate assessment results.

Illuminating Shady Industry Conduct

While it is widely reported that many volume builders and building design professionals actively discourage and pressure NatHERS Assessors to exclude shading in their energy rating modelling, this practice is unacceptably misleading for the consumer and perilous ground for the Assessor.

Assessors are bound by their Code of Conduct to perform their work with the highest level of professionalism and in accordance with the practices outlined in the NatHERS Technical Note. When Assessors are subject to a Quality Assurance review, their projects are measured against the technical note and, therefore they are at risk of losing their accreditation should they fail... there is a lot at stake.

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...the shade cast onto a dwelling can limit the amount of sun or solar radiation striking a building, thus affect the ambient temperature inside the dwelling.

NatHERS Technical Note provides processes to ensure consistent and reliable Home Energy Ratings.

The NatHERS Technical Notes can be likened to the systems and procedures that have made McDonald’s Golden Arches an international phenomenon. Like McDonald’s systems and procedures, the NatHERS Technical Notes provide robust scaffolding that guides NatHERS Assessor best practice resulting in a consistent, reliable and repeatable product.

For example, we can be reasonably certain about the kind of experience we can expect when visiting McDonalds... the branding and signage are consistent and immediately recognisable, car parking is plentiful, inviting and surrounded by manicured gardens, we can expect certain items on the menu and that those items will look and taste the same no matter if we visit a store in Woolloongabba, Woolloomooloo, West Wyalong or Washington DC... the decor is the same, bathrooms will be clean, and the smiling server at the front counter will ask “would you like fries with that”!

Similarly, the Technical Notes are intended to guide consistent modelling practices across the industry so that building surveyors, regulators and industry at large can be confident the data provided via the NatHERS Certificate is accurate and a reliable measure of the proposed dwelling’s demand on the energy grid and carbon footprint. The consumer can be confident they will get what they have paid for and deserve... a dwelling where the home’s thermal efficiency, seasonal comfort and ongoing energy running costs can be reasonably predictable. This notion is becoming more and more important with expanding reliance on NatHERS Star Rating reports as evidence of a building’s sustainability measures for the likes of the financial sector Green Home Loans and the expected introduction of mandatory disclosure of a dwelling’s energy efficiency rating at point of sale and rental.

So what does the NatHERS Technical Note deem as shading?

As mentioned earlier, shading in NatHERS modelling is complex and there are many elements to be considered. Shading devices can be elements of the building itself or can be separate to the building.

Examples of elements of the dwelling itself that cast shade include eaves and gutters, pergolas, verandas, outdoor living areas, glazed or solid screens, supporting devices such as brick pillars and any part of the building that casts shade on another part of the building at any time during the day.

Similarly, examples of detached shading elements include fences, neighbouring walls, heritage listed protected vegetation and neighbouring buildings. There are also provisions and guidelines in the Technical Notes and Handbook to include projected future buildings when modelling a home in a new, unpopulated estate.

Assessors and Building Designers can refer to Upper Case Section 10 of the NatHERS Technical Notes 2019 and Section 9 of the NatHERS Handbook 2019 for rules and guidance on modelling shading.