Towards Nearly Zero Energy (non domestic) Buildings


Non Domestic building standards are generally considered to be difficult to develop and address. The diversity and breadth of possible building types can be vast and as a result of this complexity, new standards get less attention and consideration compared to the easier to handle domestic sector. This post looks at some of the complexities and discusses what could be improved and what needs to be in place before the end of 2020…

The United Kingdom is subject to the European Performance of Buildings Directive (EPBD recast), which sets requirements for new buildings to be ‘Nearly Zero-Energy Buildings’ (NZEB) by 2019 for new public buildings, or by 2021 for all new buildings.

We have four years to develop a clear definition of what a ‘Nearly Zero-Energy (non-domestic) Building’ is and how it can be achieved in a cost-optimal way; We need to develop minimum energy performance requirements and presumably, as with domestic proposals, there will be a part-way carbon compliance level developed based on what is cost optimal to do on-site, set somewhere between where we are now and actual full-on on-site Zero Energy, with the rest of the energy consumption offset through allowable solutions. Improved efficiencies, improved services and a contribution from renewables will all be necessary.

A quick overview of the current state of the regional non-domestic standards:

  • The Welsh Standards introduced in 2014 added a Target Primary Energy Consumption requirement for non-domestic buildings, which represents a targeted 10% improvement in primary energy consumption.
  • The Scottish 2015 Standards improved the target roof, walls and floor levels in the NCM building model. They also introduced more stringent targets for shell and fit buildings.
  • The last England non-domestic new build uplift was 9% on aggregate over 2010 levels, with notional building amended accordingly. The Welsh pushed further and adopted a 20% step change. The Scottish have taken a 43% step forward for their new 2015 standards over their 2011 standards, which were already pretty good.
  • There was no uplift to extensions, refurbishments or windows and no consequential improvements changes in the last English standards changes, whereas the Welsh introduced more stringent requirements for extensions to buildings that are essentially ‘domestic in character’. The Scottish non domestic extension targets go beyond those required in England.

The last 2013 English building standards  were developed against a government commitment to not increase regulatory burden and so was limited in scope, which means there will be a big step needed for 2019. Whilst the economic reasoning for the last small step is obvious, it is not realistic in the longer term to expect no additional cost for N-ZEB.

There will be a higher cost attached to achieving (nearly) zero energy, but that should in large part be offset by the operational cost savings from better performing buildings.

There is a massive variation in the types that constitute non-domestic buildings and it is this complexity that makes setting standards for them so difficult. Different non domestic building types can have very different requirements and demands; the building fabric can be cost effectively improved upon for some building types fairly easily, especially where broadly similar to domestic dwellings in nature; but for others, the heating demand is minimal and improving the fabric might be counterproductive.

Which leads one to the answer that different building types should have different targets. What is cost optimal for one type, will not be for another.

The variety of building types possible and the differing ways that they are heated, cooled, lit, glazed and insulated suggests that different categories of building types should have differing targets and expectations. Air tightness levels and to some extent services efficiency levels do differ in the current National Calculation Methodology target setting, but fabric levels could also differ, with tailoring for different building types and demands.

The Scottish 2015 Standards set differing targets for Heated and for Cooled buildings, and it would be reasonably simple to set different building fabric targets for ‘Side-lit heated and naturally ventilated’, for ‘Side lit heated & mechanically cooled’ and for ‘Top-lit’ building types for England too. Other building categories could also be considered, with differing fabric, services and renewables levels used for each in setting cost optimal targets that could be achieved.

The fabric targets for elements of the Welsh and new Scottish standards have already pushed beyond the English 2013 standards and we should carefully look at those as regards cost effectiveness and associated reductions in emissions and energy demand.

The Welsh 2014 standards development of a Target Primary Energy Consumption (TPEC) for the 2014 Notional Building is one that should be explored in more detail. This approach is a similar idea to the English Domestic standards Target Fabric Energy Efficiency in that it ensures an overall reduced level of primary energy consumption through improved building fabric and services and an associated reduction in demand before considering offsetting residual emissions from services and renewables.

For some building types, building fabric improvements have a comparatively small effect on emissions and costs within SBEM (especially compared to lighting usually), but in most cases improved levels do have an effect and for those broadly domestic in character, improved levels can be very beneficial.

I firmly believe that we shouldn’t be trying to compensate for a poor fabric through larger amounts of renewables; a huge initial heating and cooling demand means that somewhere along the way, higher carbon emissions and costs will result from that high demand, which is wasteful. Reducing demand from the outset and then adding renewables and improved systems to that firm base is a much better approach overall for cost savings and for emissions savings.

Some people have concerns that making some buildings more expensive to build might make some projects less viable and could stifle construction growth; however if buildings are going to achieve Zero Carbon, or Near Zero Energy levels, we will have to appreciate that there will be some costs attached to doing that, it is unrealistic to expect otherwise.

It is important to note that buildings with reduced energy demand, also have reduced operational costs and minimal maintenance costs alongside the environmental and sustainability considerations.

It’s time to start looking at non-domestic buildings properly and spending the time and money necessary to do it right, rather than just ignoring it until the last minute and wondering why it’s still not working very well.

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Jon Ducker is a qualified energy assessor working for Kingspan Insulation Ltd. He has an extensive knowledge of energy efficiency, renewable energy systems and sustainability in buildings with an expert knowledge of the relevant sections of buildings regulations and standards and their interactions with SAP. He provides authoritative advice regarding energy assessments for a wide range of public and private sector clients.

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