Watch our webinar in partnership with Medite Smartply, which explores how successful approaches to design, specification and procurement can benefit clients, building users, and the environment.

The problem of getting to net zero carbon has to be attacked from two directions. We need commitment from governments, legislation and enforcement. And to complement this top-down approach we need a bottom-up one that looks at the detail of specification on individual buildings and at ways to ensure that they are built to a high enough standard to make them behave in the way that they were designed to.

So, it was appropriate that this webinar on intelligent specification for zero carbon talked about the scale of the problem and also got into the nitty-gritty of registering the presence of every potential air penetration in the construction of a new-build house in County Wexford.

Speakers from left to right: Daria Blanc-Mathieu, Isabel Barros, David Murray, and Pat Barry

Pat Barry, chief executive officer of the Irish Green Building Council, outlined the scale of the problem. The construction sector is responsible for about 39% of CO2 emissions, he said, 28% occupational and 11% embodied carbon. And the global building floor area is expected to double by 2060, so that emissions per square metre will have to be cut even more severely to compensate for the growth in floorspace.

Initial findings from a study by University College Dublin showed that Ireland reflects the global pattern, with construction accounting for 35% of total CO2 emissions, of which 24% is occupational and 11% embodied. With the move towards better-performing buildings, and to greener energy, it is vital, Barry said, that we tackle the question of embodied carbon in our buildings – in the materials used, their transport to site, and the way that they are assembled.

Carbon Designer – early design tool

‘Over the next couple of years,’ he said, ‘we will need a revolution in materials and construction methodology. We will have to have incredible levels of innovation. One of the barriers that we see is that every architect has to be up-skilled to understand how they reduce embodied carbon. That will require simple tools that allow them to evaluate at an early design stage how one type compares to another.’

Even if the architects are not going to be carrying out detailed analysis, Barry said, they must understand the implications of decisions at the concept stage. To help with this, the Irish Green Building Council is introducing a free tool called ‘Carbon Designer: early design tool’.

60 years embodied and operational carbon output for a typical office

Barry’s revolution in materials is something that Daria Blanc-Mathieu is trying to bring about. She is a senior sustainability consultant with Meehan Green, an independent consultant company that specialises in green building certification and life-cycle assessment.

It is important, she said, that specifiers know which building materials to target. The most obviously appealing choices are, she said, bio-based or natural materials. In addition to advantages of lower carbon emissions for manufacturing and the fact that the materials are renewable, there is the bonus of biogenic/ sequestered carbon. This is the CO2 that is absorbed by the growing material. However, Blanc-Mathieu warned, this has to be reported separately in a life-cycle analysis, because of uncertainty about how it will be used at the end of the building’s life.

Embodied carbon for different floor slab options

She reminded the audience that, while timber is what we think of first when considering bio-based materials, there are others, including hempcrete, straw bales, rammed earth and even structures made with tubes of recycled paper.n In each case it is important to assess materials in terms of their life-cycle analysis, and make the best choice. And when one starts looking at embodied carbon in a building, there may be some surprises. Blanc-Mathieu gave the example of a typical office building in Dublin with a steel structure. The most important material in terms of emissions was steel, followed, unsurprisingly, by ready-mix concrete. And in third place? The raised floor. This becomes more comprehensible when you consider the replacement cycle. In a 60-year design life, this floor will be replaced at least twice.

 Infographic showing the process of carbon sequestration in wood panels

David Murray, head of technical affairs and Ireland sales at Medite Smartply, said, ‘Wood is the carbon-smart building material. But it is only the right choice if it has been sustainably sourced, used in a resource-efficient way and if all of the required quality and sustainability standards have been met.’

Graph showing the embodied carbon footprint of SMARTPLY PROPASSIV with breakdown of transport, materials and processes

He outlined the processes that his company goes through to make MDF and OSB from timber thinnings, and went into more detail about another of the company’s products, Smartply Propassiv. This is being used on an exemplar case study: a high-performance Passivhaus in County Wexford, designed by Isabel Barros Architects.

Passive House at Crossabeg, County Wexford, designed by Isabel Barros Architects

Barros was also a speaker. She described the process of design and construction on this, the practice’s first Passivhaus. ‘We were worried abut being restricted by boxy volumes,’ she said. ‘But as soon as we did the concept design, and consulted our Passivhaus consultant, we were very pleased to discover that our creativity didn’t have to be restricted.’

Passive House, erection of timber frame 

She described the technical approach to ensuring that there were no thermal bridges and that the building was airtight, both of which were vital. The contractor, she said, had a special notebook pinned on the wall on which every member of the team listed every penetration, so that it could be sealed.

It is this attention to detail that we need if we are get to net zero CO2 – along, of course, with some national and international commitments.