Retrofit in construction explained: What it is, why it's needed, and how to ensure you do what's right for your house

What is retrofit in construction?

Retrofit refers to the process of improving an existing building to reduce its energy use and associated carbon emissions. This is typically achieved through measures that enhance the building’s energy efficiency, such as insulation and draughtproofing, or by replacing fossil fuel-based systems with low- or zero-carbon alternatives. The overall aim of retrofit is to reduce the environmental impact of buildings while improving their performance.

Why is retrofit important?

For the UK to reach Net Zero – a term that has built in ambiguity; net, not gross to allow for offsetting and UK based to avoid the inclusion of ‘imported carbon’ – there will still need to be radical interventions across all sectors. For the construction sector, to reach net zero by 2050 we will need to do more than just build our new homes differently; we will have to decarbonise our existing housing stock, because 80% of the buildings we will be using in 2050 have already been built, and they all use too much energy.

Knocking them all down and starting again is not an option – for many reasons – but from a carbon perspective, it’s because there are two ways of measuring the carbon footprint of a building; the carbon used over its lifetime, heating / cooling it, lighting it and running all the appliances within it; and the embodied carbon in its manufacture (the carbon used in building it). The only alternative is therefore to improve their performance in some way.

How can energy demand be reduced?

Energy demand can be reduced in three main ways: improving the building fabric, upgrading building services, and changing occupant behaviour. Retrofit relates specifically to the first two of these. Measures such as insulating walls, roofs and floors, or improving airtightness, reduce heat loss and therefore the amount of energy required to maintain comfortable conditions.

In parallel, existing heating systems—such as gas boilers—can be replaced with lower-carbon technologies, predominantly now air source heat pumps, and buildings can generate their own renewable energy through systems such as solar photovoltaic panels. These are just two of many options, and there are new solutions and improvements to existing ones being made all the time, making the best course of action sometimes difficult to calculate.

How is it paid for?

Unlike behaviour change, which can reduce energy use without financial cost, retrofit generally requires an upfront investment. This cost is often offset over time through lower energy bills, commonly referred to as the “payback period”. For this reason, a staged approach is often recommended, prioritising cost-effective measures – but with the emphasis on those that reduce heat loss and improve ventilation being carried out before investing in new energy generation or heating systems. Grants available to help finance new heat pump installations should only be available to those whose homes are ‘heat pump ready’.

What retrofit options are there?

Retrofit options also vary widely depending on the building type, condition and occupancy, so to find the most appropriate solution, independent, up-to-date advice is an important first step. While people’s motivations for retrofitting differ - cost savings, improved comfort, energy security - all retrofit activity contributes to reducing emissions from the built environment and tackling climate change. But it is important to understand how different buildings function before making any changes, because it is easy to do more damage than good, or at the very least, spend a considerable amount of money for very little reduction in energy bills.

Victorian properties are particularly difficult to retrofit because they are built with solid walls with no cavity to fill or to stop moisture travelling across from outside to inside. Normally, these walls dry out naturally before damp and then mould becomes a problem, but retrofitting can cause problems. Making a house more airtight by reducing draughts also means more moisture can build up inside than can work its way out through the walls. Insulating those walls with the wrong materials, ones that stop that moisture escaping altogether, can then makes this problem even worse.

Using the right materials, ones that are ‘breathable’ and let the moisture pass through, and using mechanical ventilation to extract the moist air from kitchens and bathrooms, means these problems can be avoided, but seeking advice is an essential first step.

Where can the best advice be found?

All solutions will be promoted as the best solution, all contractors will favour those they have most knowledge of, and access to funding will always trump appropriateness for your building or your lifestyle. Objective research is difficult to carry out with so much conflicting information readily available, but websites promoting sustainability for the good of the planet, rather than specific products for the good of their manufacturers, will always be the safest bet. Always check for objectivity, credibility and currency – the internet can be a graveyard of historical data sources.

What new technologies look promising but aren’t yet on the market?

Plus there’s always something ‘on the horizon’ promising to rescue us, but the danger here is ‘doing nothing’ whilst waiting for something that may never arrive. The best antidote for this is to fully research future solutions now, and not to blindly live in hope of salvation. Infrared Fabric is a solution on the near horizon, although still not fully accredited - but when it is, it may well be the solution Victorian homeowners have been waiting for.

Dr Mike Siebert is a Lecturer in Architecture at the School of Architecture, Design and Built Environment