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Building Performance in Practice

Small House, Heavenly Court

The “Small House” was one of the first projects ever certified by eTool. Key features of the original 3 bedroom design included a lightweight timber frame, small 2 storey footprint and 6 star NatHERS thermal performance rating. John and Betty Saunders moved into the house in December 2012 and we thought it was time to pay them a little visit and see how the house is actually performing. There is a large gap perceived in the building industry between performance ‘As Designed’ and ‘As Built’. eTool has committed to auditing 1% of all projects. Through checking ‘As Built’ drawings, energy bills and site visits we hope to gain a better understanding of where anomalies lie and hopefully help bridge the performance gap.

Initial Reactions

Approaching the dwelling from the main road it clearly stands out amongst its surroundings. The double storey building sits on a plot much smaller than its neighbours whilst still boasting a large garden space. The use of space is far more economical than neighbouring buildings which mostly stretch right to the boundary of their plots – there is even room for a number of fruit trees and native plants which are scattered around the edges of the lawn.

Stepping into the house it is obvious that the design has been carefully thought through. The large north facing windows and open plan layout allow for plenty of natural daylight and the temperature on this fairly chilly July morning is very comfortable. John informs me that they have not required heating all winter – quite impressive for a building that only passes the current regulatory thermal performance requirement of 6 stars. Walking around the house it is barely noticeable that there are almost no windows on the south facing wall as the main rooms are located towards the north. The master bedroom does have a westerly facing window which will let in a lot of heat during summer months, however it also provides good cross-flow ventilation from the afternoon sea breeze and there are plans to install a pergola over the window. The Saunders only require the reverse cycle heat pump during the very warm 32 degree plus days when there is little breeze.


Real data has been obtained in the form of energy bills which combined with an audit of all appliances provides a reasonable picture of what the main uses of electricity are. The last electricity bills show a consumption averaging 5kWh per day which is 75% less than the average of 15 units for 2 person households in the area. Including the generation from PV which is likely to offset most of the daytime consumption, the total electricity consumption is estimated at around 7.3 units which is pretty close to the 8.4 units predicted by eTool LCA during the design stages.


Small House LCD 2


As well as a reduction in the energy required for thermal comfort, the house has lower carbon impacts associated with cooking. This is because an electric cooker and stove was assumed in design stages whereas a gas stove and electric oven have actually been installed. (For further info on gas versus electricity see here). There are also a number of ‘smart’ appliances including:-

Refrigerator – as well as being in a well ventilated space (for more on fridge ventilation see here) the fridge has a “holiday mode” as well as sounding an alarm when the door is left open.

Kettle – the kettle has the ability to set the temperature required. Any tea or coffee aficionados amongst you will know that the perfect coffee temperature is around 90 degrees and the perfect tea around 80. This simple function has relatively large savings due to the fact that it takes much more energy to convert water to steam (at boiling point) than it does to heat water by a single degree.

Drying line – The garage was not in the original design and adds slightly to the embodied energy of the building, however the side doors are located such that a good through draft occurs in the afternoon which is perfect for drying clothes without worrying about the rain.

The increase in the “other” category is largely down to the sophistication of the calculation during the design stage. This appliances template has since been updated a number of times and now splits the other category further into dishwasher, clothes dryers, workshops and all other appliances.

The embodied impacts are close to those predicted during design stages. There is an increase in the fittings category due to embodied impacts of electrical and light fixtures not being accounted for originally.  The increase in internal finish is because the buildings’ ground floor is finished with ceramic tiles which were not assumed in the design stage.

Silver medal house, gold medal people

The building as designed represents a 52% CO2e saving over the benchmark which is an eTool Silver Medal rating.  As built, the building does much better, achieving a 116% saving which is an eTool Gold Medal rating

The performance of the Small House is down to a lot more than good design. The Saunders are clearly conscious of their own environmental footprint and feel strongly that “if today’s humans don’t live more sustainably, then our children and grandchildren will suffer the consequences”. They have a sustainable lifestyle that aligns closely with their sustainable home – their electric scooters, for example, (powered by batteries charged from the PV panels) get them to Bunbury and back on a single charge and they even purchase large bags of fruit on offer and use a de-hydrator so that they keep for longer. According to NatHERS a 6 star house of this size should require around 3000MJ per year to maintain thermal comfort, however John and Betty require only around half of this. Although there are obvious deficiencies in the NatHERS methodology[1] the key difference is down to occupant behaviour more than anything else. The eTool Medal rating has risen to Gold because the occupants are making the best with what they have. Likewise it is all too easy for a house to be designed to Gold standards but fall far below that in practise because the occupants have all the gear and no idea.

This raises a very important point – as engineers we focus primarily on good, low carbon design and innovation, however occupant behaviour has an equally important role to play in reducing our environmental impacts. Persuading people to put an extra jumper on in the winter perhaps presents a far greater challenge than some of the more tangible aspects of delivering a low carbon society.

Read the original case study of Heavenly Court here >>


[1] Namely a lack of monitored data to support the calculations, questionable accounting for thermal mass, lack of air-tightness or thermal bridging calculations, no account of equipment efficiency or fuel source.

ESD Australia

Design Vs Actual Performance

Does the design really perform once the software model is complete and the occupants move in?

In the design space there are so many models and tools we can use to help inform the way we create our buildings. But as much as we like to put our faith in our design skills, there are lots of assumptions, model boundaries, data limitations, user errors and uncontrollable variables (like the building occupants). So while don’t really like to admit it, there is still a mild level of finger crossing when we get to review the real performance of a building in operation. At eTool we’ve put nearly four years into developing our “Life Cycle Design” methodology within the “eTool LCA” design software but we are still learning and improving.

So when we get to review our buildings a few years on and find that they are performing as predicted, we have a little mini celebration inside, and on the outside say “yep… always knew it would”. What’s really nice is to then feed that information back into the model to help refine those assumptions, boundaries, data limitations and most importantly improve the skills of  the ‘designer’.

A fantastic example of this process is ESD Australia, one of Western Australia’s leading building consultancy firms, specialising in energy and building compliance for residential and commercial developments.

With some other commercial rating systems out of reach budget wise for small commercial buildings, eTool LCA proved the perfect (and arguably more comprehensive) solution for the ESD Australia team when designing their own new office. The building design had great functionality with good service life and occupancy, combined with good material selection, high thermal performance and small scale renewable energy generation. The end result was a building that was predicted to produce more energy than it consumed with a 114% improvement in carbon footprint on a “compliant” design.

“It was great to be able to use eTool and a “Life Cycle Design” approach to see how the entire building might perform rather than just the individual elements that other rating systems focus on. Now that we’ve been operating in the building for 2 years, it’s wonderful to see the building performing as expected with a 6 NABERS rating and reaffirming our design choice,” says Daniel Smee, Director, ESD Australia.

NABERS is a government administered national rating system that provides a platform for rating commercial buildings against their performance through analysis of actual energy bills rather than a modelled design. It’s a rating out of six stars so ESD Australia’s office is considered to be “market-leading”. It shows that by utilising eTool LCA in the design process you are not only achieve fantastic outcomes but also can predict with confidence how you will perform against NABERS once built.

At eTool, we like to say “it’s better to be vaguely right rather than to be precisely wrong”. I guess what we mean is that as long as the end result is a better building than what was originally proposed then we are happy even if it’s not 100% spot on. The great thing about the process is that for every project we work on we have a lovely feedback loop that ensures that everyone who uses the “eTool LCA” design software gains from this knowledge and collectively improving the buildings we design.

So, while we will always do some finger crossing once we hand over the design to the occupants, we are enjoying the confidence that our buildings are continuing to improve and are performing better than predicted.