Zero Carbon Buildings

Achieving Net Zero Carbon Buildings in just Four Steps…

The pathway to net zero carbon buildings has been extended to include embodied carbon (materials carbon). This is because the embodied carbon content can be more than 40 times the size of operating carbon emissions. Chasing operating carbon mitigation frequently has the effect of bringing carbon forward and may never in reality be “paid back”. The net result, more carbon, not less.

This demonstrates the significant improvement in access to and quality of materials carbon data. Whilst still somewhat a “black box”, there are four simple lessons to adopt and strategies to avoid to deliver substantial whole of life carbon reductions without cost.

By 2030, over 135 billion m2 of new building is needed just to accommodate growth in global population. This could account for over 350 gigatonnes of embodied carbon emissions. Consistently halving the embodied carbon content of new buildings and adaptively re-using a sizeable proportion of existing stock, is possible when design is supported by strategic LCA and adopting most of the four main pathways to low carbon design. Achieving this reduction could contribute about half of the overall emission reduction needed to achieve the Paris Agreement targets.

 

Figure 1 – Embodied Carbon content of building types (kg CO2 / m2 NFA)

 

Figure 1 shows the average embodied (materials) and operating carbon content of various Australian building types. These figures show the absolute amount of embodied carbon for the base building and fit out creation against one year of operating carbon. It can been seen that the ratio of operating to embodied carbon varies between 55 for office to 40 for retail and residential. That is, the building needs to exist and be operated for 55 years for the annual emissions to equal the material impact of development. Interestingly, the reality in Australia is that over 55% of all residential stock is less than 30 years old and commercial stock 27 years, and retail tenancies less than 5.

To halve the embodied carbon content of new building, there are four key steps:

Step 1 – Realistic Life Cycle

Most structures and facade are specified with a lifespan of more than 50 years. This can add more than 20% to the embodied carbon footprint. As shown, the average life span of buildings in Australia is less than this. The key here is to consider a) the realistic service life and design to this and b) to adopt a design strategy which allows for the majority of the structure and facade to otherwise be adaptively re-purposed or amended “insitu”. Adopting this approach for the structure and facade has the potential to avoid 15-35% of future carbon impact.

Step 2 – Alternative Solutions

It is possible to reduce the carbon intensity of buildings by over 30% by adopting key design strategies. The structure, facade and services of most buildings account for 30-45% of the total building carbon impact and each of these has alternative solutions which may vary more than 50% depending on the approach. A simple cross laminate timber structure can reduce total impact by 40% as compared to a traditional concrete structure.

Step 3 – Recycled Content

Adopting high recycled content in many materials can reduce carbon footprint by more than 60%. Care is needed as even some 100% recycled content materials may still have more carbon than a virgin material for the same use (e.g. polyester insulation over recycled glass or recycled nylon carpet versus timber planks).

Step 4 – Low Carbon Supply Chain

Five years ago the concept of supply chain of custody for timber products was unknown. Today it a requirement. Procuring key building materials from low carbon sources can avoid 50% or more of the carbon impact. Knowing which materials to focus on and what to specify is essential to get a result. For example, the difference between aluminium fully produced in Australia, versus Western Europe or Canada is three to one in terms of embodied carbon content per tonne.

Conclusion

Almost half of the embodied carbon footprint of buildings gets “locked away” within the very first few days of schematic design so adopting all of these strategies is essential in order to at least halve the carbon footprint of new buildings. Achieving this could provide a no cost / low cost solution to achieving a fair measure of the Paris Agreement targets.

Ideally, designers and owners need ready access to simply data and visual guides much like those you could expect in Cordell’s Price Guide or Rider’s Digest. The GreenBook and The Footprint Calculator by The Footprint Company are two possible sources of this sort of information.