Net Zero Carbon Buildings, Not Zero Energy Buildings

Originally posted on Irish Green Building Council blog.

The proposed amendment to the Climate Action and Low Carbon Development, will set a demanding trajectory for Ireland in order to achieve net zero carbon emissions by 2050. When considering this, it’s important to remember that zero carbon does not mean zero energy, so it is inevitable that a net zero carbon building will consume energy, unless you live in a cave.

The replacement of fossil fuel with renewable energy to power the grid is a difficult but essential component of the Zero Carbon strategy, however, it is only part of it. Those of us in the built environment must recognise that we cannot truly achieve net zero as an industry unless the buildings we design, operate at the minimum energy intensity as well. But what does this mean and how do we achieve it?

In my opinion, a net zero carbon building should consume no more energy than is required to keep the occupants healthy and comfortable, without compromising the operation of the building. Since we have been ‘optimising’ buildings’ energy efficiency for years, you would expect that they already perform at their optimum energy intensity. However, the problem is that as an industry, we don’t typically know how they perform and indeed, we rarely even bother to even check.

The first step is to set a clear target that focuses designers on the issues. The current Part L calculations are woefully inadequate in terms of predicting energy consumption because this was never their purpose. For the same reason, BREEAM Certification has underperformed in this area. In my opinion, we would be better as an industry to adopt the successful Australia NABERS energy rating system. A NABERS 6-star rating targets very low levels of energy intensity and equates to over 70% less energy consumption compared to a current equivalent best practice building.

It is important to remember that there is no silver bullet when it comes to achieving net zero, just incremental improvements. To achieve these low energy intensity levels, we need to consider a wide range of issues including, low levels of glazing, PassivHaus envelope, natural ventilation, flexible internal temperatures, heat scavenging, and heat pumps, among other considerations. Using the NABERS methodology allows the benefits of each of these measures to be realistically assessed, so that the available budget can be focused where the greatest carbon reduction might be achieved.

Embodied carbon is a challenge, and a range of targets are being proposed for different timelines, some of which are not achievable. There is a current a growing trend towards the use of timber as a low-carbon alternative building material. Timber is a fantastic material for construction, not least for its biophilic benefits, and while it comes with many challenges (cost, fire retardancy, acoustics etc), these can all be overcome.

There is a long way to go to achieve our ambitions and reach a zero carbon future for Ireland’s built environment. The challenges in achieving this goal are vast and should not be underestimated, but this doesn’t mean net zero carbon buildings are an impossible challenge. It is comforting to know that engineers/designers, all over the globe, are working to find solutions for this problem, and that through innovation and evidence-based design, as well as industry collaboration, significant progress toward our net zero carbon future is just around the corner.