"It's terribly simple," said Paul King. "A zero carbon building is one that is designed to be highly energy efficient in terms of its fabric, services and appliances. We should then meet the residual energy demand from renewables."
As chief executive of the UK Green Buildings Council, King is uniquely placed to explain the trajectory to acheive zero-carbon buildings. All new homes and schools will need to be zero-carbon by 2016, and all new public sector buildings by 2018.
"The zero carbon targets represent a fundamental change in mindset, an absolute goal that [requires] no net increase in emissions from new buildings," said King. "Ambitious targets like zero carbon provide certainty, and clarity of the direction of travel for investors and innovators"
However King warned that the construction industry has been stuck in a cycle of incremental improvements: "the art of what we do and doing it just a little bit better rather than any fundamental break from the past," he argued. "There's a disconnect between what we aim to do and the scale of the real challenge that we need to respond to.
As Michael Kelly, professor of technology at Cambridge University and a chief scientific advisor to the department for Communities and Local Government, pointed out, is that new build will only tackle 10 per cent of the problem.
"More than 60 per cent of buildings will still be standing in 2050, so we need to focus on tackling the existing stock," said Kelly.
"We need to radically transform the efficiency of existing housing, but we can't carry on doing up a 100 houses here and there. Instead we need a programme to tackle a million houses, because we'll only have a chance to do one or two makeovers of our existing stock on a significant scale between now and 2050," he added.
Kelly called for the creation of a retrofit consortium, a body charged with ensuring the renovation market adopts low and zero-carbon materials and processes.
"If the MoD, the education sector, local government and social housing bodies can come together to create a credible pull-through agency, we could scale up the volume of triple glazing for example, and get the price down to that of double glazing today," he said.
Patrick Bellew, head of engineering consulant firm atelier ten, agreed that a cultural change is necessary, as well as changes to the way low energy and renewables technology is funded and applied.
"Is it appropriate" he asked, "for every building to be an autonomous biome, because this question gets to the root of how we are going to define the zero-carbon building."
Bellew argued that whatever passive design or active low energy technologies are used, there is still a residual 20 per cent carbon load that you cannot design out.
"No matter how hard we try, we get to a point in building design where we spend more money than we need to per tonne of carbon saved," he said. "We could do a lot better by spending it elsewhere.
"My proposal is to use the Section 106 planning process to offset the residual carbon emissions. [Developers] could invest, say, £500 000 into a community fund that pays for a programme of solar panels right around the borough," suggested Bellew.
Architect Bill Gething of Feilden Clegg Bradley Studios argued for the industry to "get real" about the current levels of energy efficiency. "Gas for catering and electricity for ICT is normally excluded from our energy benchmarks, but can add up to more energy used elsewhere in the building," he said.
"Architects and engineers sweat blood trying to get buildings to use less energy by specifying clever lighting systems and other services, while others in the world are creating equipment that uses vast amounts of energy.
"It's no longer a case of playing the system and just getting buildings to comply with the Building Regulations, added Gething: "We need a big plan about how we will allocate the scarce resources of the future; at the moment we don't have that plan."
Gething argued for the energy performance data for buildings to be exempt from the Data Protection Act. "This is a public interest issue and should be freely available so we can all learn from it," he proposed.
Simon McWhirter of of WWF reminded delegates that we are living beyond our means, and that we are taking more away than the planet has the ability to restock and replenish.
"We are behaving as if we have limitless resources to draw upon," he said. "If we continue to push our demands at the current rate we will need two planets to survive within 30 years."
McWhirter agreed that while there are bigger emitters of carbon dioxide around the world."The UK is a small but canny player on the world stage," he said.
"As a nation we have a track record of success against the odds. We are incredible innovators, so it's time to stop preaching about what needs to be done and deliver the vision for a one planet future."
There was nothing magical about truly sustainable buildings, added McWhirter. They are simply better ones.
"We don't need to sell people into deep green lifestyles or set them on the pathway to eco-enlightement," he said. "Sustainable buildings should be designed to be appealing, gentler on our pockets in terms of running costs, gentler on our health in terms of improved internal environment, and much more gentle on the planet."