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By Willow Aliento
November 28, 2017
There’s a growing buzz about carbon neutral buildings, especially since the Australian federal government has recently defined a standard for them under the National Carbon Offset Standard.
But how exactly do you build one? Jobsite spoke to one of the leading experts on the topic, the Green Building Council of Australia, to find out.
The GBCA’s Senior Manager of Green Star Solutions Nicole Sullivan explains there are two main approaches.
The first one is pretty much business as usual. On completion, the owner of the building purchases bulk carbon offsets to balance the embodied carbon and ongoing operational carbon emissions from energy use.
“This is not best practice,” Sullivan says.
The better approach starts with achieving at least the level of energy efficiency stipulated in the NCOS standard, as the standard specifically applies to operational emissions.
For most buildings today, Sullivan says, operational emissions will actually account for between 70 and 80 per cent of the total lifecycle carbon emissions.
To reduce embodied carbon in the form of the building’s fabric and systems as well as operational carbon, one of the things that should be considered is the need to invest more in materials, she says. “You need to make sure you make responsible choices.”
That includes using low carbon materials if possible.
That shopping list can include timbers and engineered wood products, lower footprint concretes, certified recycled steel and aluminium products, bricks from a carbon neutral supplier, natural stone products, and plastics made from recycled consumer waste.
“There are better and worse choices in materials. Timber is a good choice because it is a carbon sink – the carbon in the timber is locked up in the building for the life of the building, she says. “But other materials have benefits as well – and you can’t just build out of one material.”
Recycled products often have a much lower carbon footprint than those made from new raw materials. Aluminium, for example, uses around ten times more energy to manufacture from raw bauxite ore than it does to recycle used aluminium into new products.
This has been highlighted by the glazing industry in New Zealand, which has a stewardship scheme for aluminium framing used for windows in both residential and commercial buildings.
When it comes to concrete, Sullivan says, using only standard Portland cement is not the best choice.
There are a number of alternatives. One of them are products with high slag or fly ash concrete. Another is geopolymer concrete, which was successfully used in buildings including the Global Change Institute at the University of Queensland in Brisbane, which took on the highly prescriptive Living Building Challenge. Under the LBC rules, a building must achieve net zero for energy and net zero for water, as well as meet criteria around carbon, toxins, and beauty.
At Toowoomba, geopolymer concrete developed by Wagners was used by the company’s owners to build the new Wellcamp Brisbane West Airport, including the runways, aprons, and airport buildings.
Another option for concrete is the mixes that use supplementary cementitious materials, such as slag and fly ash, sourced from waste streams of the steel industry and coal-fired power stations. Sullivan says concrete containing up to 30 per cent of these types of materials is now “relatively common in good buildings.”
Sullivan says another option is to use some materials that have a high embodied carbon load but to use them very efficiently. High strength steel and high strength concrete, for instance, reduce the quantity of the material that is needed to do the job.
Glazing products ideally need to be high performance, such as double glazing or low-e, to ensure energy efficiency. This can add a little to the budget.
With steel for beams and other elements, Sullivan says optimised products rather than generic off-the-shelf ones are a better choice. Optimised steel products may enable beams to be slimmed down or tapered, using less steel overall, if this is factored into the engineering design.
Building systems can include technologies that save or recover energy, such as regenerative drive lifts, which use a similar principle to state-of-the-art vehicle braking systems to feed energy back into the electrical system. Some new water drainage systems can recover energy when water flows through the pipes.
There are also passive energy-saving initiatives to consider, such as the use of architectural shading systems to reduce thermal gain on the facade of a building.
“Shading is a valuable investment,” Sullivan says.
She says that using lifecycle analysis on the specified materials can show what the return on investment will be in terms of energy use and consequent reductions in carbon emissions.
Sullivan points out that any change in building practices means there is a learning curve involved.
There may also be trade-offs to factor in, for example an alternative concrete may take longer to cure, and this needs to be factored into the works program.
“A helpful thing is to go on site tours so you get an inside look at what the latest trends are,” she says. There are also webinars that can be tapped into.
Another thing builders and trades can do is talk to suppliers and find out what they can do for you when it comes to lower-carbon products and technologies.
“Manufacturing is in a tough market – and it is looking for market signals,” Sullivan says. “If we want low carbon or certified carbon neutral products, we need to demand it from suppliers as the market.”
Because the building industry does generally operate with lead times between specification and actual arrival of materials on site, there is time for many suppliers to adjust when requested. For example, Lendlease, in delivering the carbon neutral Barangaroo precinct, worked closely with suppliers from the outset to achieve the best outcomes for its procurement.
Compliance and quality workmanship are also crucial, Sullivan says.
One of the best tools for ensuring this is BIM, as it offers vast opportunities in terms of being able to manage what is going into the building and record checks of compliance and completion.
“Commissioning plans are also incredibly important.”
It is also better to do all the checking for defects and other issues and rectifying them as early as possible during a build. According to Sullivan, “if you leave it to near practical completion, it is harder to rectify things.”
There are also additional processes that can be used as part of the checking process. In the Green Star – Design & As Built rating tool, for example, there are some points reliant on a project undertaking air tightness testing.
“There are a lot of buildings that resemble cheese graters.”
Sullivan says the GBCA’s aim is to incentivise an industry that is capable of doing air-tightness testing cost-effectively and pragmatically, hence the Green Star requirement.
“You don’t have to do 40 floors, it’s a bit of a pragmatic approach.”
Sullivan says that all the various trades increasingly understand that what they do influences the overall performance of the final building. “It’s not rocket science. We have the technology and tools to deliver carbon neutral buildings now. What we need is the desire and the passion.”
Sullivan says that tackling the carbon neutral building challenge and green building generally is important for recruiting and retaining the new generation entering the industry, as they have a heightened concern about environmental sustainability. There is also a challenge for the forerunners in sustainability, that is to say in how green building is positioned.
“We need to present sustainability as not being some fringe green thing,” Sullivan says.
Because buildings don’t exist without people, the social aspect of building matters too, as does the need for green building to make economic sense.
“In terms of large scale change, it can only happen if we can demonstrate the economic benefit.”
Aspects like increased productivity of people within green buildings and the proven uplift in building values are part of the business case.
“We need to get better at communicating that to convince those clients that are into the return on investment. We need to talk about green building differently.”
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