Low Energy Retrofit of UK Housing

By Carrie Behar

View of Sustainable Architecture Festival Venue

RIBA London Sustainable Architecture Festival

Above photo by: Carrie Behar. Used by permission.

Design professionals have enormous potential to make a positive impact when working on low energy refurbishment projects, but are also faced with a multitude of challenges, including limited budgets and conflicting priorities.

In September 2019, Carrie Behar spoke on the subject in the first RIBA  Architecture Festival, hosted by Stirling Prize nominees, Feilden Fowles at Oasis Farm Waterloo.  Some of the key points of her presentation, which considered the role of architects in the large scale retrofit of UK housing, are discussed below.

Why do we need to retrofit our housing to use less energy?

In 2019 the Committee on Climate Change published a report about the state of the UK’s housing. One of its five key recommendations is that all of our existing homes need to be made low-carbon, low-energy and resilient to a changing climate. The UK has the least energy efficient housing stock in Europe. There are around 29 million homes in the UK and together they make up for of our carbon emissions; to achieve our Climate Change Act commitments to reduce UK carbon emissions by 80% before 2050, we’re going to have to tackle housing. Almost 90% of the housing in the UK today will still be here in 2050; Therefore, most of our current housing stock needs to be radically transformed – it’s not enough to just ensure our new housing is zero carbon!

Refurbish or demolish and rebuild?

One question that comes up often is whether it wouldn’t just be easier to demolish all our existing, inefficient housing stock and start again with modern homes which are designed to be energy efficient and sustainable.

There are several reasons why there is a strong case for refurbishing, instead of demolishing, historic buildings.  Existing housing contains strong communities which have formed over generations, and there’s enormous heritage value in our housing stock; currently 4.6% of homes in the UK are in Conservation Areas and 1.5% are Listed.

But there are some strong environmental benefits to retrofitting too. New and existing houses both contain embodied carbon in the building fabric –that’s the carbon that goes into making all the construction materials, shipping them to, and assembling them all on, site. The embodied carbon in existing buildings is already ‘spent’ and cannot be returned (except through recycling or reuse, something we are not good at – see below). That means any new materials (either for retrofitting, or a new building) carry additional embodied carbon. Therefore, minimising additional material is one of the most effective ways to limit an increase in embodied carbon. In addition, materials like concrete and steel, which are currently some of the cheapest materials with which to build new UK housing stock with, have a particularly high embodied carbon content compared to timber frames and locally sourced bricks, which is what many historic buildings are made of.

Finally, we are currently not very good at recycling or reusing the waste that arises from demolishing buildings – it often ends up either in landfill or in a lower value use than originally, such as aggregate for cement or cut and fill.

Approaches to retrofit

First and foremost, low energy retrofit is about reducing the need for space heating, which accounts for about 60% of domestic energy demand (the rest is lighting and appliances). In 2015 the Green Building Council warned that we need to retrofit 2000 homes per day between then and 2050 (that’s over 2.7 homes per minute…). Here are some examples of what a retrofit project could entail.

‘Deep’ retrofit

A ‘deep’ retrofit typically achieves a CO2 reduction of at least 80%. To do this, the dwelling needs to be made as airtight as possible, with the addition of numerous fabric interventions such as internal and/or external insulation for walls and roofs, new glazing, mechanical ventilation with heat recovery, and extensive draft proofing of junctions and joints. This often entails bespoke detailing and relies on there being a committed client with a large budget. It is time consuming, messy and disruptive, and is not a good model for mass retrofit.

‘Light touch’ retrofit

In contrast, something as simple as properly insulating the loft, can save as much as 20% of energy bills, can cost as little as a couple of hundred pounds and may take just a few hours or days. However, we’ve already insulated more than half of our lofts in the UK, so there’s only so much more that can be saved in this way.  We are going to have to start finding ways to tackle the ‘hard to treat’ homes – which are those with solid (i.e. uninsulated) walls.

Putting a price on carbon savings

So how do you persuade people and landlords to retrofit their solid-walled properties? While loft insulation is cheap enough to offer an immediate cost saving on energy bills, both internal and external wall insulation is much higher, and is unlikely to be recovered through energy savings alone.

As the financial case for deep retrofit without subsidies is weak, trying to persuade homeowners to carry out a retrofit to save money on bills isn’t going to work. Luckily, energy and carbon savings aren’t the only benefits and drivers of retrofit projects. As well as the carbon impacts, a good quality retrofit can have additional benefits – including upgrading substandard housing to improve the comfort, health and wellbeing of the residents. We know that a huge number of people in the UK are currently living in substandard accommodation, which has poor consequences for their health; cold damp homes exacerbate conditions like asthma and can lead to respiratory infections and additional winter deaths. In rental properties, lower bills are critical in reducing fuel poverty, particularly as cold homes are estimated to cost the NHS £1Bn per year (£3.6M/ day).  Based on this there is a strong economic case for government to subsidise the retrofit of fuel poor households.

Scaling up – meeting the 2050 targets

Where does this leave us? As built environment professionals we are always juggling a whole range of factors to come up with the best possible solutions – it’s not straightforward at all. Here are a few suggestions for planning your own retrofit project:

  • Engage clients about wider benefits of retrofit; it’s not just about climate change
  • Look out for incentives and subsidies to make retrofit pay
  • Work with experienced contractors who understand airtight detailing
  • Focus on the fabric as it’ll last longer than M&E technologies

Share This:

Facebook Twitter Google+ LinkedIn