26 June 2014 — The Fifth Estate has been paying attention to the growing number of tall buildings on our city skylines. In terms of densification and transport tall buildings are a sustainable plus. But how much effort are the designers, engineers and developers putting into making them more sustainable? And how do they compare with medium-density projects? In this part of a special report series focusing on residential tall towers, Willow Aliento takes a closer look at tall buildings in the residential space.
According to Dr Robert Crawford, senior lecturer in construction and environmental assessment at The University of Melbourne, the way space is allocated within concrete and steel building envelopes through to people’s penchant for changing major parts of the interior on a regular basis is just not adding up to a green picture.
Crawford has undertaken extensive research using hybrid lifecycle analysis into the materials and energy footprints of residential dwellings, and has published a number of studies that compare detached dwellings in the outer suburbs with medium-density inner city and high-density inner city apartments.
In terms of the differences between the medium-density and high-density options, the basic embodied energy footprints of the materials themselves are not substantially different if both are using concrete and steel.
“The thing that changes is the amount of materials changes. High rise means more mass per square metre, because there is a greater load on the building, so you need more concrete and steel to support the load,” Crawford says.
Because there is also more wind load on a high rise, more bracing is required, which again adds to the footprint. And there is also generally more resources used in the services such as the lifts, and increased amounts of ductwork and electrical systems, which adds up to a greater amount of embodied energy and resources per resident than a medium-density, low rise building.
On the other hand, he says there may be more centralised systems in a high rise building, which may reduce the materials footprint somewhat.
Common space adds to energy footprint per person
Operational energy use is often also higher for tall buildings, mainly because of the higher use of common space, in addition to private space.
“And all the common space increases the energy use per capita,” Crawford says.
This can include corridors, lift lobbies, foyers, fire stairs and car parks, as well as any resident amenities such as pools, lounge areas, media rooms, event spaces and gymnasiums. In terms of both energy use and embodied energy, these can add considerably to a high rise building lifecycle footprint.
But the upside is it’s often easier to make a tall building dense, and people do tend to live in smaller spaces in high rise. If you get twice the density, energy demand might be higher but you can house more people in a small area.
Another question is how are the common spaces used?
Crawford says there might be potential for the pool, for instance, to be used by the wider community.
“Combining community facilities within the building reduces the energy footprint per capita,” he says.
“When you integrate a community facility such as a childcare centre in a building it decreases the energy impact per person and space is not needed for those facilities elsewhere.
“There are things you can do to make them more sustainable.”
The transport proximity factor
Proximity to public transport and employment are also two elements Crawford factors in to his lifecycle energy footprint analysis. Where high rise residential is located near both of these things, it does reduce the per capita energy footprint compared to a detached dwelling in the outer suburbs, where transport is a major part of the occupant footprint.
In the paper Impact of past and future residential housing development patterns on energy demand and related emissions Crawford co-author with Dr Robert Fuller, a comparison was made between a typical seven energy star detached dwelling in the outer suburbs, the medium density K2 apartment development and a typical 20-storey Docklands apartment building with an average apartment size of 100 square metres for two bedrooms, constructed of reinforced concrete with a high proportion of glazed facade.
The analysis of the embodied energy, which included materials, direct energy used during construction, plus the EE of capital equipment, goods and services used in the construction process plus the energy use including transport of occupants during the lifecycle, showed that the Docklands building had a bigger footprint than both the medium-density and the detached dwelling.
The high rise apartment had an EE of 23.33 gigajoules a sq m of useable floor area, compared to 21.78 GJ a sq m for K2 and 15.62 GJ a sq m for the detached house. This analysis also showed the high rise generated the highest greenhouse gas emissions, of four tonnes per person per year.
Crawford says that high rise developments in central activity zones, such as in Melbourne’s Footscray and Dandenong that are evolving into small CBDs, can slow the impact of energy use, as transport is one of the largest demands for energy use in the urban context. But, he says, “You’ve got to have the jobs there.”
You can’t design occupant behaviour
However, there is one factor he says design can’t manage, and that is the behaviour of people in a space.
“In terms of operational energy consumption, behavioural factors are one of the greatest influences in the operational energy footprint. People are the elephant in the room – and the most difficult thing to deal with,” Crawford says.
“With a low rise project you can shade the windows for thermal efficiency and so on, but the person in the home might still use heaps of energy. Behaviour is difficult to control. You can recommend how people use a space, but there are so many things design can’t control. A high rise tends to have more centralised systems, so they might be easier to control.”
Coal is at the root of the energy issue
“Really, energy is only an issue because it comes from fossil fuels. If we had high rises with renewable energy, energy efficiency would not be as big an environmental issue,” Crawford says.
He said high rise allowed the capture of wind, and was not shaded in regards to capturing solar energy, and in the UK and Indonesia there were high rise residential buildings with big turbines integrated into the structure of the building.
An example of this is the Strata Tower in London, which is the tallest residential building in the city. The tower features three giant turbines in the roof, which theoretically were going to provide up to eight per cent of the building’s total energy needs – enough to power the lifts, base building lighting and base building mechanical systems. However, issues around noise from the buyers of the penthouses just below the turbines mean they are inoperative for substantial parts of every day, and have not met their energy generation target.
In the Australian context, smaller wind turbines have been installed on buildings including the Australian Catholic University’s 6 Star Green Star Daniel Mannix Building in Melbourne, where the turbines in combination with solar PV are providing part of the building’s energy requirements. The combined renewable energy system was assessed by ACU as having reduced energy costs by $35,000 in the first few months of operation.
Sustainability still not on the home buyers’ shopping list
Crawford says that having spoken with many developers, it is clear that one of the big obstacles to these and other innovations is developers are essentially building what the market demands, and at this point, energy efficiency is not on the average buyer’s shopping list. Podium level and rooftop landscaping with trees and grass, yes, that the market can be sold on, but right now energy is a harder proposition.
When solar feed in tariffs were high, solar photovoltaics and solar hot water had a more obvious business case, he says, and at that point demand did drive the sector. However, now it is a case of selling it to buyers on the basis of lower ongoing costs.
Early design collaboration essential
The built-in base building sustainability aspects such as cross ventilation and passive solar orientation are all elements Crawford says need to be part of the early design.
“It’s got to be integrated; it’s got to be thought about at the beginning,” Crawford says. “In an ideal world we would make all decisions earlier, not just bolt them on. They shouldn’t be bolt on, because when the budget gets cut, they get cut out.”
He gives the new architecture building at the University of Melbourne as an example of the benefits of early design stage integration of green initiatives.
“It was all designed around pedagogical design, because we want it to be teaching the students, and around passive design.”
- See our article University of Melbourne scores its first 6 Star building, with full innovation points
The short and brutish lifecycle of interior elements
Another aspect of high rise residential where the environmental impact looms large is the interior fitout.
“Fitout is quite significant in embodied energy terms, especially the things that get replaced every 10-15 years such as carpet, paint and kitchens,” Crawford says.
“The initial impact of a building is in the concrete and steel, and the longer the building lasts, the more the recurrent embodied energy of the fitout becomes important. Ten yearly replacements of paints and carpets add up and become quite significant in terms of embodied materials energy, especially if you are using resource intensive and polluting materials like vinyls and laminates. That’s why the lifecycle of materials is important.”
In terms of fitout materials that are low in embodied energy, Crawford says timber and cellulose based products, being also renewable and recyclable, are the only ones that rate well. Even rock and stone, though natural, are finite materials, whereas given the right choice of species, and a rate of use that is lower than the rate of growth of the resource, timber is sustainable indefinitely.
“The materials we have to use are in a way fairly limited. There is concrete and steel, and some work is being done around mass timbers… such as Forte,” Crawford says.
“We have the ability to build high rise with mass timber. The main thing is making sure the buildings are adaptable and reasonably easy to refurbish, as people will want upgrades every 10 to 15 years. For example, you can use clip on and clip off wall panels.
- See our article Timber: the next evolution in construction
“Generally, you need to choose materials which are easy to recycle or are recycled and last as long as possible. Steel is preferable to concrete, as it is easier to recycle. Glazing systems, generally the glass is long lasting, although the seals around the glass do usually need replacing, as they can fail within 10 years, and they are not easy to replace when they are up high.
“And if you are using fly ash in concrete, it reduces the carbon footprint of the concrete, but fly ash comes from coal fired power stations.” This means the footprint of the coal burning waste product has simply been displaced into the concrete, which overall is not necessarily an embodied energy win.
Are we making them worse?
The current focus on improving the building envelope through the use of expansive glazing for natural light and increased insulation for thermal efficiency, he says, may actually be making buildings worse in terms of embodied energy, as these are also materials which are resource-intensive and high in embodied energy.
“Most materials are finite – so more insulation or glazing is not necessarily good,” Crawford says.
One of his current research projects is the lifecycle implications of reducing operational energy use in buildings.
“I don’t think any of the buildings we’re designing go far enough [in terms of sustainability],” he says. “I really don’t like to use the word ‘sustainable’, because even in Green Star buildings we are still using concrete, steel and plastics which are not in the real meaning of the word sustainable – the resources are finite.
“You can keep putting PVs in and saying that’s sustainable, but it’s all the other things people are not talking about that are the problem. With steel and concrete, what happens when we run out of iron ore?
“Sustainability is a word that gets misused. We need to consider the planet and the raw materials we’ve got – timber is the only thing that can grow. The other materials which are currently being used are mostly all from fossil fuels and finite raw materials.
“We need other materials.
“Sustainability is a word that gets misused. We need to consider the planet and the raw materials we’ve got – timber is the only thing that can grow”
“Buildings have become so advanced, they need systems which involve things like precious metals and those systems – including solar panels – are energy-intensive to produce.”
There are other architectures and building styles that are both energy efficient and use low embodied energy materials, such as adobe, mud brick and straw bale, but Crawford says these and other typologies are at variance with current urban and marketplace expectations.
“We’ve known how to design buildings to operate efficiently for centuries, but it’s only that our expectations got so high, and we can do things now like control the temperature to 21 degrees year round and so we do have those expectations that we will control it.
“We’ve managed to separate buildings from people.
“We need to look at how our needs might be better met from buildings. With the more high-tech buildings it is difficult to interact with our buildings, and it is difficult to control our buildings.
“Our problem as human beings is we like to quantify things. We like to prove things, so we can say ‘but it feels better’ and then the question is asked, ‘But how much better?’
“How do we measure that ‘better’? And when money’s at stake, as it is with developments, how do we value that?”