Disclose NatHERS Before Mandating Disclosure 2

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Tuesday, September 15th, 2015
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Mandatory Disclosure
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It has recently come to light that the Victorian Government, in their desire to improve the energy efficiency of residential properties, is considering introducing mandatory disclosure of the energy performance of dwellings.

This will require that potential tenants would be provided with information on how much their prospective new home is likely to cost them in energy bills.

I think this is a fantastic idea; it would certainly put pressure on both developers and landlords to improve the status quo of what’s being built. There are so many social benefits to having an improved building stock, particularly when it’s targeted at residential properties of lower income households.

But first we need to ensure that the methods in place for assessing the energy efficiency of these developments is up to the mark. Otherwise, we run the risk of producing misinformation with undesirable consequences.

Existing dwellings would need to have sufficient energy audits completed; it won’t be enough to collect energy bills from past tenants since there is so much uncertainty around whether that resident was a ‘typical’ consumer of energy or had (for instance) a solarium in their cellar. The energy audit would need to investigate the thermal performance of the build construction and determine the expected energy bills based on climate data.

New-build dwellings would also rely heavily on modelling, based on the hypothetical thermal performance of the yet-to-be-built construction.

The existing methodology for assessing the energy efficiency of a new-build dwelling, NatHERS, is currently far from ideal. The calculation assessment is a black-box insofar as even accredited energy modellers have no idea on the calculations behind it. There needs to be far more transparency in the process before we can introduce a mandatory disclosure process, otherwise how can we be capable of providing suitable design advice?

There are numerous things that are challenging around the current methodology of determining thermal performance, but my top three recommendations for improving the process would be:

Introduce audits of new-build dwellings, including air pressure testing

Air pressure testing involves an on-site test to determine how ‘leaky’ the building is, which can have a huge impact on the energy consumption of a building. If you cannot control it, you waste heated air during the winter and lose cooled air during the summer. The tightness of the building is determined by the quality of build, which can be greatly improved with sufficient sub-contractor coordination. Thermographic imaging upon completion could also be an extra driver to encourage quality of build.

Account for thermal bridging of building fabric

Thermal bridging is a term used to describe areas of higher heat transfer in the building fabric. It takes place at junctions between different constructions or different fabric materials, such as the aluminium frames of spandrel panels, the metal studs in a plasterboard wall, or the connection between a wall and floor. Currently, these types of extra heat flows are not taken into consideration in the NCC, and they can have a large impact on not only the energy consumption, but the thermal comfort of the dwelling.

Release the NatHERS calculation for review and revision

We need to ensure that the calculation procedure is fit for purpose; there may be some unclear and questionable assumptions in NatHERS, including the mysterious ‘floor area correction factor’ and the additional factors related to windows that are invisible to the energy assessor. In addition, the different software options need to be equivalent; it is wholly unacceptable to have different software providing different results, which can mean the difference between a pass and a fail (as is currently the case).

Clearly there’s a vast amount of room for improvement to be had in the process, but it’s encouraging that a state government is stepping up to drive energy efficiency of building stock. If it’s implemented correctly, I’m all for it.

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2
  1. Daryl Hargreaves

    Spot on Jessica
    'The existing methodology for assessing the energy efficiency of a new-build dwelling, NatHERS, is currently far from ideal. The calculation assessment is a black-box insofar as even accredited energy modellers have no idea on the calculations behind it.'
    I have been an accredited energy rater since 2002 & am now no longer accredited. The Victorian government, in their wisdom, mandated that every energy rater should have to undergo a Cert IV course to standardise qualifications. I and half the experience energy raters in Victoria have decided not to comply with this cash grab from a Government hell bent on appearing green. The idea that a $4000 – 6000 course & 75 – 100 hours of my time spent learning what I already know is somehow beneficial to the green economy is ridiculous at best. The end result is you will now have less experienced energy raters charging more for their reports while the building designers who have been in the industry for many years no longer provide this additional service. Added to this, each time the software is updated the older ratings no longer comply, leading me to assume that no ratings done in the last 13 years actually comply

  2. Matt Ryan

    The idea of mandatory disclosure is very very important! Builders compete in a market directly against the established housing stock.

    If builders are being pushed to raise the bar with energy efficiency they need to be able to justify why the new building is more expensive.

    It would be good if the builders could use the higher standards as a marketing point of difference.

    From a Banking point of view. The banks need to value new builds higher. At the moment there is no bench mark to base pricing on. Therefore customer can't get their extra provisions funded.

    Regarding AccuRate assessments. We find the Chaneth engine to be quite good, there are some issues around inputs however. Fibreglass insulation is significantly overrated and the use of brick and concrete also seems to be heavily weighted.

    Our suggestion is to use the more advanced US standard (ASTM1363 Full Wall Testing). By doing this we would eliminate input inaccuracies and at the same time fix issues around thermal bridging.

    Why reinvent the wheel!

    Nathers is trying to start generation 3 AccuRate at the moment hopefully it will be funded by the feds.

    Successive governments have turned a blind eye to this issue we are operating on a system which was once installed by 3 1/4 floppy discs.