Retrofit or New Build?

Whichever is the case, it is more likely than not that your building will still be in use in 2050. In fact 80% of the buildings with us today will still be in use in 2050. The energy consumption of existing buildings accounts for around 34% of the UK’s annual carbon emissions and we all need to be considering ways of reducing the carbon footprint of our buildings.

Much attention is paid to new-build performance and, although challenging, we know how to construct new ultra-low energy “net zero carbon compatible” buildings. These buildings are designed and built to minimise carbon emissions throughout their lifecycle and meet tough embodied carbon and energy use intensity targets, as part of the UK Net Zero Carbon Building Standard (previously set by LETI and RIBA’s 2030 challenge).

While we would urge everyone thinking of commissioning a new building to include net zero carbon in their brief, the real elephant in the room is how to go about reducing carbon emissions from our existing building stock. The embodied carbon associated with a new building is on average twice that of a deep retrofit, so retrofit should always be prioritised where it can be. The question for the custodians of existing buildings should not be whether to retrofit, but how deep and how soon to retrofit!

A retrofit involves the installation of an element or technology into an existing building which wasn’t there previously. It’s commonly used to describe an upgrading of elements within a building, such as thermal insulation or replacement of the heating system technology to improve efficiency and reduce carbon emissions.

There are different drivers to retrofit, including:

• An organisation’s or individual’s desire to reduce their carbon emissions
• Improved comfort, health and wellbeing
• Reduction in energy bills
• Minimising resource consumption through a circular economy approach encouraging “retrofit first”
• Minimum Energy Efficiency Standards (MEES) for private rented properties set limits on the energy performance ratings allowed. The legal minimum Energy Performance Certificate for non-domestic properties is currently set at E moving to C by 2027 and B by 2030, affecting 85% of rented non-domestic properties
• ESG investing and Green finance has also become mainstream – mortgage rates are just one example where it will shortly be cheaper if your building is greener
• Some Local Authorities are now introducing planning policies that make replacing a building more difficult, requiring substantive justification considering resource efficiency
• Public attitudes to retention of buildings is becoming stronger and increasingly important

A significant proportion of the carbon emissions associated with buildings arise from the materials used and the construction process itself, these are the “embodied carbon emissions” of a building. Extending the lifespan of a sound existing building which is capable of adaptation to meet an occupier’s future needs is almost certainly a lower carbon pathway than demolishing and building new. The embodied carbon associated with the construction of a typical new building can be equivalent to 20 years' worth of its operational carbon emissions, in the future as our new buildings tend towards ultra low operational energy consumption, then this could conceivably stretch to 40 years. Over the timeframe of 10-30 years (depending on the particular deadline for net zero) then it is likely that retrofitting existing buildings, where possible, will have a more positive impact on climate change than building new.

It may also be possible to intensify sites through retrofit and partial new build without knocking down and replacing, or it may be the existing building may work better for an alternative use.

Getting the right help

The first step is to understand the impact of your building and the opportunities to reduce its impact on the climate. Getting advice from a professional designer skilled in retrofit, or a retrofit coordinator, would be a good place to start. Initial activities might include:

• Energy consumption analysis and benchmarking using utility data
• A thermographic survey to identify fabric performance
• A survey of existing services

How far do you go?

It may be tempting to take only the simplest in a retrofit, however a considered approach to achieving the greatest outcomes should always be taken. A “deep” retrofit should always be the aim but it may be that a 70-80% carbon emissions reduction can be achieved rapidly and more cost effectively through a targeted approach of fabric interventions and heat decarbonisation. With a large estate this is likely to be the way to achieve reductions on a large scale quickly.

Retrofit works will likely interrupt normal use of the building, but completed retrofit measures will lock-in performance well into the future, so it is important to get it right the first time. Retrofit should aim to maximise the feasible performance and aim for as close to new-build net zero carbon compatible performance as possible.

Useful resources

Retrofit performance standards such as the AECB’s Building Standard or the Passivhaus Institute’s EnerPHit certification could help provide target performance levels and act as a guide to retrofit.

Many institutions and organisations will be eligible for funding through the Salix Public Sector Decarbonisation Scheme or the Social Housing Retrofit Accelerator which has specific requirements that should be considered when planning the approach.

For domestic properties a good reference is the LETI Climate Retrofit Guide for homes published in 2021 setting out six key principles to follow, recommended performance standards for different typologies, and recommended process for implementing a whole house Retrofit Plan.

Planning the complete retrofit in advance, rather than tackling piecemeal improvements, will help ensure that successive measures work in harmony and are implemented in a sensible order. It may also identify measures that might be tackled at the next maintenance cycle more cost effectively.

The retrofit hierarchy

The retrofit hierarchy diagram shows the order in which you should approach a retrofit.

Minimising energy demands through improvements to the building’s thermal insulation, glazing, air tightness and ventilation systems should be a first step. Significant energy demand reductions can also be achieved through efficient lighting and controls, solar shading, using pumps and fans with EC direct drive motors and selecting equipment such as IT systems specifically for low energy consumption. Replacing sanitaryware to reduce hot water consumption is often overlooked but a cost effective way to reduce energy and save water.

Reducing energy demands initially will make subsequent improvements like replacing gas boilers with heat pumps cheaper with lower operational energy costs.

Finally, consider generating your own energy through technologies such as solar PV panels. Integration of a demand-side response (DSR) strategy with or without energy storage could further reduce energy costs, consume grid electricity at times of lowest carbon emissions and even generate income.

The challenge of ending carbon emissions is enormous and we need to accelerate the pace of change. Big UK banks and investors are setting out their environmental credentials and although legislation forcing improvements on buildings owners is currently limited, this will undoubtedly evolve. In the meantime, we need pioneering organisations, building owners and occupiers to take up the retrofit challenge and influence positive change.