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How to do a Section J Assessment as a NatHERS Assessor?

by | Apr 15, 2020 | NatHERS

What is Section J?

Section J is the part of the National Construction Code that covers the Energy Efficiency of Commercial (i.e. Class 2-9) buildings.  The aim of the legislation is to reduce Australia’s greenhouse gas emissions by ensuring that buildings and their services have features that facilitate the efficient use of energy.  Several tools are available to assessors to demonstrate compliance with the Section J Performance Requirements:

  • A Performance Solution (either directly or via a Verification Method in the NCC e.g. NABERS for Class 5 Offices, or JV3 Modelling)
  • A Deemed to Satisfy (DTS) Solution (following Parts J0 – J8)
  • A combination of Methods (e.g. Roof requirements met by Performance Solution, remainder by Deemed To Satisfy)

Any one of these assessment tools can be used to demonstrate a compliant building design.  Although the term Section J covers all of these types, when people refer to “a Section J Assessment”, they almost always mean the Deemed to Satisfy Assessment. Parts J0-J8 of the NCC provide a set of reference values or requirements – if any building satisfies all these values it is ‘Deemed to Satisfy’ the Performance requirements of the legislation. The rest of this article will discuss how this works.

How do you do a Section J DTS assessment?

Under NCC 2019 Vol 1 (which comes into mandatory effect on May 1, 2020), the DTS approach provides for assessment of each of these components of the design:

  • Thermal Construction (Part J1.2)
  • Roof and Ceiling Construction (Part J1.3)
  • Roof Lights (Part J1.4)
  • Walls and Glazing (Part J1.5)
  • Floors (J1.6)
  • Building Sealing (J3)
  • Air-conditioning and Ventilation System (Part J5)
  • Lighting and Power (Part J6, J7 & J8)

In completing a Section J DTS Assessment (also known as a JV3 Assessment), you need to show that the building to be assessed complies with each section of the NCC Requirements.  The method used is similar to a domestic DTS Assessment, but there are some significant differences due to the different ways that commercial buildings are expected to be used.

The area of the building being assessed is only the “Conditioned Envelope” (with the exception of J6 – lighting).  The Conditioned Envelope is different to the Building Envelope and is only those parts of the building which are conditioned or are ‘reasonably likely’ to be controlled by air conditioning.

Unless an assessor has the specific skills or background required, it is normal practice for thermal performance assessors to exclude Part J5 (Air-conditioning and ventilation) from their assessment.  In this case, the Mechanical Engineer specifying the system will provide the compliance and completion documents for this Part.

Most sections are fairly straightforward, however, careful reading and understanding of the legislation is required at all points to make sure all elements of the building are being assessed properly with regard to the Climate Zone, Conditioned envelope, and Building Class.

The exception to the “fairly straightforward” comment above is the way Walls and Glazing are treated.  There are big changes in the NCC 2019 code.  Two of the more important ones are:

  • Walls and glazing are treated as a single component – a “Wall Glazing Construction”. This makes assessments more complex than under previous versions of the code, but there are also new opportunities (under DTS) to ‘trade off’ various design components and orientations.   Under the new code, a ‘Maximum U-Value’ and Glazing SHGC cannot be exceeded for the whole building averaged across all orientations, along with minimum requirements for wall R-Value.
  • All calculations for roofs and wall insulation must now take into account ‘thermal bridging’ caused by the wall frame. Steel framing (for example) is a poor insulator and will ‘compromise’ the performance of wall insulation by providing channels for heat to leak through the wall (i.e. thermal bridging).  Under NCC 2019 this thermal bridging must be quantified and taken into account when assessing a wall or roof.  It can have a big effect, sometimes halving the value of the insulation in the wall!

The resulting calculation is quite complex, and it is perhaps harder to see how to improve the situation if the wall-glazing calculations do not pass the requirements with the inputs that the client is hoping to use.

Please note that at the date of writing (10 April 2020), the Australian Building Codes Board (ABCB) has still not issued a final Wall-glazing Calculator.  The current beta version does have some errors in it, and it is not recommended that you use it for Assessments.

When would you do one (and when wouldn’t you)?

Every new building in Australia requires an Energy Efficiency Assessment as part of the certification/approval process.  So the simple answer here, is that you do one when a client asks for one!

A Section J DTS Assessment is almost always a lower cost assessment than obtaining a JV3 or NABERS or GreenStar Assessment. So when would you do one?  Whenever you can!  That said, the cost of the assessment needs to be weighed against any increase in building materials that may result from a Section J DTS Assessment.  This may happen for example where there is a floor of the conditioned envelope above open air that always requires additional insulation with a Section J Assessment, and may not with a JV3 assessment.   Or the design might have a large amount of glazing on one small facade, resulting in specialty glazing.

With the NCC 2016 and previous issues, the generally accepted wisdom was that Section J Assessments were suitable for basic commercial buildings, such as simple childcare centres or real estate offices.  Any buildings with large amounts of glazing such as car dealerships or office blocks were considered more suitable for a JV3 assessment, as the glazing calculator was too difficult to pass.

With the NCC 2019, there is a special allowance for display glazing, and this combined with the treatment of the wall-glazing system as a whole does mean that there are possibly more types of buildings that are suitable for a Section J DTS Assessment.  This is certainly the case where all the glazing is on one facade, as there is the option to consider all the facades as an average (as opposed to individually).

As Assessors gain more experience with the new 2019 legislation, they will become more competent in advising clients as to whether they believe the project will be most suitable for a Performance Solution or a Section J DTS Assessment.

If your client is particularly keen to maximise and understand how to get their building to perform more efficiently, there is always the option for them to increase the efficiency of certain elements beyond the DTS Requirements, such as installing more insulation in the roof/ceiling construction than is required, or having glazing that performs better than the Wall-glazing Calculations requires.  The other option in this situation is for clients to obtain a Performance solution such as a JV3 assessment.

Who can do one?

Anyone who is deemed competent to complete an Assessment by a Certifying authority is able to do a Section J DTS Assessment. This would generally require that the individual has the knowledge and skills, and often the qualification in a relevant field. Practically, if the certifier considers the individual who undertakes the assessment to be competent, then they are. You just need to satisfy the regulator or regulatory requirements certifying authority.

It is a good side step for a NatHERS Assessor to undertake Section J Assessments when things are quiet with regular NatHERS Assessments. Likewise, it can be a great option to expand your service offerings beyond NatHERS Assessments.

Tips for Section J Assessments

For those who already complete Residential DTS or JV3 Assessments, the skills required are not onerous, although the calculations and reporting are more complex.  Time is required to read the legislation carefully, engage in some training and provide evidence to any Certifying Authority who requests it that you are competent to undertake these assessments.

  • Take care to understand the Vol 1 definition of a conditioned envelope as it differs from Vol 2.
  • Confirm the conditioned envelope with your client before you proceed with your assessment as it affects everything you will calculate.
  • Use the hyperlinked definitions in the (free) downloadable copy of the NCC 2019. When clarity seems lacking, it is almost always to be found by reading the legislation section carefully, and following through all the definitions of terms used, both in the legislation and the definitions themselves.
  • Understand what your clients are wanting so that you can best assist them. Obviously, your report will show what is required, but look for ways to help them understand how the Section J Assessment works and how they can best achieve their design or build in the way they want.
  • For large or complex buildings, it is recommended to involve the energy assessor much earlier in the design phase so that any Energy Efficiency design requirements can be incorporated early on in the process.

What other tips can you suggest?

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