TG Escapes Blog
What is a Net Zero Carbon Building?
Net Zero in use or in construction?
The term Net Zero is becoming familiar to many but it can mean different things to different people. In the context of the built environment, it is used to describe both buildings that are Net Zero Carbon in operation and those that are Net Zero Carbon in their construction. Here we explain the difference and outline the steps that TG Escapes and others in the industry are taking to help tackle climate change.
In 2008, the UK became the first major economy in the world to pass into law international commitments to end its contribution to global warming by 2050. The Climate Change Act 2008, and its 2019 amendment to comply with the 2016 Paris Agreement for Climate Change, commits the UK to bringing all greenhouse gas emissions to net-zero. Any emissions that cannot be prevented by this time must be balanced by schemes to offset an equivalent amount of greenhouse gases, such as planting trees or using technology like carbon capture and storage. During this period, the signs of climate change have become increasingly widespread and the term net-zero carbon has entered mainstream awareness and language. However, it has yet to be categorically defined and means different things to different organisations, corporate and governmental, and civil groups and individuals.
Why is the construction industry so keen to move to Net Zero?
Globally, the built environment sector is currently responsible for almost half of greenhouse gas emissions so, clearly, if the Government’s commitment is to be achieved then the British construction industry needs to urgently address the issues of energy-efficient building design and construction process within a net-zero context. However, the concept of a net-zero building is one subject to differing interpretations and meaning. Some focus purely on the energy consumed during a building’s day to day use, some on the creation of the structure and others still on the entire life span of a building from the laying of the first foundation through to its demolition and removal. We will clarify what we think will eventually qualify as a net-zero building, once policy is set.
The UK Green Building Council (UKGBC) has been playing a vital role in developing a workable definition to assist the construction industry in its development of buildings that achieve the net-zero carbon objective. In its document “Net Zero Carbon Buildings: A Framework Definition” they have adopted a two-pronged approach to defining a net-zero building, comprising operational use and construction practice, the latter often accounting for half or more of a building’s carbon emissions.
Net Zero Definitions
The starting point for net-zero construction definition is:
“when the amount of carbon emissions associated with a building’s product and construction stages up to practical completion is zero or negative, through the use of offsets or the net export of onsite renewable energy.”
Likewise, the current definition for a building’s in use energy is:
“when the amount of carbon emissions associated with the building’s operational energy on an annual basis is zero or negative.”
Operational energy includes heating and cooling systems, cooking, lighting and plug loads. Construction energy should incorporate the potential costs of adaptability and flexibility and the impact of deconstruction. This considers the total carbon emissions created through construction, adaption and deconstruction over the building’s lifetime. Only when both elements satisfy a net-zero ideal can a building be deemed to fully comply with the aims of the Climate Change Act and fit within the Government set targets of 2030 for operational net zero and the 2050 embodied target.
The disciplines and practical methods necessary to achieve the net-zero goal in construction are in the early stages of development. However, we expect to see the rapid, iterative evolution of the principles and metrics which will become subject to sharper definition, allowing for a tighter set of guidelines. The resulting system of recommended building methods, practices and policies will be created in a spirit of collaboration and consensus amongst the construction industry community including builders, designers and policymakers. The government have initiated this with specifications PAS 2050 for assessing the lifecycle greenhouse gas emissions and PAS 2060 to demonstrate carbon neutrality for certification.
Until such time as a legally binding set of net-zero building regulations is created, the general principles that the UKGBC is encouraging the construction industry to adopt are threefold.
Firstly, the polluter pays and any emissions made should, ideally, be measured and offset as they occur.
Secondly, measurement of emissions should be accurate (not estimated) and the data collected must be made available transparently and publicly.
Finally, action should take place now, before the formulation of prescriptive requirements.
SBEM and Passivhaus
The Simplified Building Energy Model (SBEM) is the Government approved software tool used by architects and designers to calculate anticipated CO2 emissions of a building at the design stage. Studies have shown that there can be a performance gap between SBEM calculated emissions and in use monitored values. This was first identified by Weber in 1997 when the gap was calculated at 30%, and more studies have shown this can be significantly higher. There are various opinions about where the performance gap comes from such as inadequate construction and maintenance or a deviation in use from the original design criteria. However, the SBEM calculations can be enhanced by looking to tried and tested commercial modelling systems such as the Passivhaus Planning Package which, when reviewed against monitored performance, was found to range within 5-10% of the calculated result with elements of overachieving.
The way forward
At present, the UKGBC stipulate that the primary priority in achieving net-zero operational energy efficiency is to reduce both the demand for and consumption of energy: that which is used should be calculable and disclosed. With regards to construction, a whole life carbon assessment should be undertaken (and disclosed) and all embodied carbon impacts from the products and construction methods used must be measured and offset. In both the use and construction of a net-zero building, every effort must be made to utilise renewable energy supplies (both on and off-site) and any remaining carbon should be offset using a recognised framework, again to be publicly disclosed.
In August 2020, The Government Property Agency issued a paper entitled “Net Zero and Sustainability: Design Guide.” Although the document is aimed specifically at the Government’s own building estate, it has drawn heavily on the UKGBC framework to identify the steps and processes that a project team should undertake to deliver a net-zero building. Until similar papers are published for the private construction sector, it is probably a good indicator of what should be expected.
Clearly, there is a lot of detail that is probably best left to the experts, but the following points cover most of the core elements of the recommendations made:
- Natural, sustainable materials should be considered first, avoiding high embodied carbon materials wherever possible and still ensuring longevity.
- Efforts should be made to use less materials generally and to reduce the weight of dead loads, thus minimising structural weight and reducing foundation load and size.
- Transportation to the build site and onsite construction should be reduced by utilising offsite construction.
- Waste and site works should be minimised and the construction materials and methods used should allow for future demounting, replacement or reuse of the structure or its elements.
- Glazing should have high U values and, where possible, have a low surface area, whilst balancing the need for natural daylight and thermal comfort. All windows should be openable to allow cross ventilation.
- All systems for heating, cooling, pumping and fans should include demand controls.
- Fossil fuelled heating and hot water systems must be avoided and renewable energy sources should be maximised. The installation of onsite renewable energy sources, and battery storage, should be considered.
TG Escapes follow a strict construction ethic of sustainability and energy efficiency and are keen to remain at the forefront of the quest to create net-zero carbon buildings that are both affordable and able to enhance the well-being of their occupants.
We already design buildings that are Net Zero in operation with the use of appropriate renewable energy technology. You can read here a detailed case study about our net-zero building at Samuel Ryder Academy. We also construct buildings that fulfil the vast majority of the recommendations made to achieve buildings that are Net Zero in construction. We are working with The Carbon Trust to certify our designs and process, and we will have that work complete in 2021. We look forward to meeting the challenges of tighter guidelines in our bid to become a net-zero company providing affordable, inspirational net-zero buildings to PAS 2060 certification.
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