Costing net zero homes

As net zero carbon becomes a guiding principle across all new buildings, creating housing stock that meets the requirements of residents, regulators and developers is a challenge, especially with so many design and construction issues yet to be solved or approaches to be standardised, says cost management specialist Rob Mills.

The built environment is a major contributor to greenhouse gas emissions, accounting for an estimated 49 per cent of the UK’s total output.

Nevertheless, new homes must be built. The government wants 300,000 homes built each year to meet demand but construction is falling far short of this goal.

The industry is tasked with meeting the dual challenge of delivering new residential buildings while reducing carbon output to neutral levels, in order to fulfil the UK’s legal requirement of producing net zero carbon emissions by 2050. Building homes to net zero standards will therefore be critical to providing much-needed housing stock while keeping the sector’s carbon emissions to a minimum.

Current guidance

As yet, there are very few completed net zero carbon housing developments of significant commercial value and scale to use as standard bearers and templates for future projects. Existing low or zero carbon developments tend to be one-off experiments, such as small projects built to Passivhaus standards.

The London Energy Transformation Initiative (LETI) current guidance is that for a residential building to be whole-life net zero, it must have a zero carbon balance for its operational activities, and be 100 per cent circular – meaning each and every one of the building’s materials and products “are made up of reused materials, and the building is designed for disassembly such that 100 per cent of its materials and products can be reused in future buildings”.

Achieving these standards will seem to many like an impossible goal. Nevertheless, it is a goal that will need to be met in the coming years for the industry to remain viable and new-build projects to be greenlit.

The industry is at a unique point in time where we know we must provide net zero developments in order for the construction sector to meet regulatory requirements and keep up with the rest of the country’s efforts to decarbonise; yet a single or an agreed set of over-arching guidance, principles and rules for creating net zero homes has not yet been fully established. Perhaps most importantly, if net zero buildings cannot be made affordable – at least not right now, at this early, experimental stage – then we also need to consider what the premium is on delivering these projects.

For a new-build project targeting net zero status in 2021, the goal therefore is to strive to meet operational and embodied carbon targets from trusted industry networks and institutions such as LETI and the RIBA, and to offset any remaining carbon.

Building For 2050

The Building For 2050 research study which is being funded by the Department for Business, Energy and Industrial Strategy, highlights the need to construct housing that is low carbon through its design rather than through reliance on technology. Being delivered by AECOM, architect Pollard Thomas Edwards, consultant Delta-EE and energy specialist Fourwalls, the project aims to understand the attitudes towards and challenges of this type of home, the costs and cost drivers associated with its construction, and the energy performance once occupied.

The findings of the research, which has focused on five developments, will be published in 2022, providing evidence to support low carbon building policy and inform future emissions reductions plans. One of those five projects is Marmalade Lane, Cambridge, a custom-built co-housing community (pictured above). Made up of 42 custom-built homes, the scheme has been designed with a fabric-first approach and passive energy design principles, delivered with offsite manufactured closed timber panels supplied by Swedish builder Trivselhus.

More information on the Building for 2050 research project can be found at: buildingfor2050.co.uk.

The future

There is an obvious need for accurate, reliable data to enable standardisation of net zero – with the goal being that the carbon value of each element of design, construction, operation and decommissioning can be easily quantified. Our Scope X^TM process addresses these gaps and helps measure critical elements of building design.

The uncertainty around what exactly constitutes a net zero homes project will soon fade. For example, residential buildings will need to be constructed to meet future Part L regulations – updates to which are in consultation, with new guidance due next year. These updated rules will help set the standard for the energy performance and carbon output of new dwellings.

Changes to Part L of the Building Regulations will also inform the upcoming Future Homes Standard, which is due to be implemented in 2025. That policy will require all new homes to be “zero carbon ready”, which will involve a huge step change in how we design and heat our homes. In the meantime, developers, contractors, suppliers and designers are tasked with meeting the net zero challenge using their own metrics and definitions – which will be influenced by existing cost models.

It is worth noting that institution-specific targets and standards are constantly evolving, further adding to the complexity of designing and building for net zero – LETI, the RIBA and the Greater London Authority are all in the process of updating and aligning their embodied carbon targets.

Regardless of which set of principles eventually becomes standardised, building net zero homes will undoubtedly require a massive shift in our collective mindset. For example, LETI advises that we begin to regard new buildings as “material resource banks” – that is, as a source of materials that can and should be used decades after the building has been decommissioned.

It is also likely that older buildings that become available for redevelopment will be treated as “donor buildings” for the future, and that we may also see specialist salvage contractors create a market through this. These concepts require us all to start thinking more imaginatively.

Net zero concepts in some ways represent a return to traditional ideas – of sourcing locally and frugally and of considering natural materials and reducing waste – yet they also demand understanding and being ready to deploy forward-looking technology and carbon-quantifying techniques to achieve and measure a successful project.

For net zero housing to move from ideas, plans and goals to a commonplace reality in the UK, adaptability and a willingness to update design and construction techniques will be required. The pay-off for those who do apply net zero principles to their residential projects is to be working at the vanguard of design, construction and building philosophy – and to be actively contributing to meeting the pressing need for a lower carbon building industry.

Clearly, for new innovation that delivers zero carbon to become more cost-effective, it needs to be implemented as mainstream practice and regulation – and we must get beyond the age-old chicken and egg.

This is an abridged version of an article that was first published in Building magazine.