How to retrofit your home (and make it more efficient)

In this blog we investigate:

  • What is retrofitting?
  • What are the benefits of retrofitting?
  • What does a whole house retrofit involve?
  • Net zero targets
  • Making an efficiency roadmap for your house
  • Grants available for retrofitting measures

If you are keen to live in a warmer, more energy efficient home, dive in!

What is retrofitting?

It means making energy efficiency measures to improve the thermal performance of a house. Key considerations for a whole house retrofit include:

  • Improving the building fabric
  • Insulating floors, walls and roofs
  • Providing adequate ventilation
  • Improving airtightness
  • Installing more efficient heating and hot water systems
  • Replacement windows or improving double glazing
  • Installing renewable heating technology, such as solar panels, an air source or ground source heat pump
A solar heating system.

What are the benefits of retrofitting a house?

  • Improved energy efficiency and reduced carbon footprint
  • A warmer, draught-free house
  • Reduced energy bills by using alternative energy sources, not fossil fuels
  • Regulated air quality means a healthy home
  • No condensation problems or mould

What does retrofitting involve?

Options include a shallow retrofit or a deep retrofit. A shallow retrofit involves simple steps such as installing low energy LED lightbulbs, smart plugs and draught-proofing windows and doors, while a deep retrofit will involve a whole house retrofit. As every house has different problems it can mean radical changes to create an entirely new system, which may include:

  • Internal wall insulation, external wall insulation, cavity wall insulation, insulating roofs and floors, being careful to avoid cold bridging at gaps and where walls meet floors.
  • Improving airtightness to minimise gaps.
  • Adding a low carbon heating and hot water system and/or renewable energy measures such as solar thermal, heat pumps or a biomass boiler.
LED lightbulb.

The cost of retrofitting

This, of course, depends on the size of house and its current energy provision: the aim is to recoup the outlay in long term savings. The cost could be between £800-£1200/m2 for a deep retrofit, according to Home Building & Renovating. For advice on procedures and costs, TrustMark, the government endorsed quality scheme covering work a consumer may have done in their home, has a downloadable guide:  A guide to retrofitting your home

How energy efficient should my home be?

An inefficient UK home may have a space heating need of over 150kWh/m2/year. To retrofit such a house to the very high EnerPHit (Passivhaus retrofit) standard, there will be a space heating need of 25kWh/m2/year. Passivhaus is a rigorous energy efficient design standard and EnerPHit is the Passivhaus certificate for achieving an energy efficient retrofit in an existing building. It takes older properties’ limitations into account and while having less onerous criteria than Passivhaus, (The Passivhaus standard is 15kWh/m2/year), it is still an exacting standard and will result in a house that can outperform a new-build home in terms of comfort and energy. With a whole house refit, it is important to plan the sequence of work correctly to avoid creating `carbon lock-in:’ EnerPHit includes a procedure to ensure that each step of the retrofit work is fully planned.

A passivhaus fitted with solar panels.

How to work out if your home is energy efficient

  • An Energy Performance Certificate (EPC) indicates energy costs and potential improvements that can be made.
  • Carry out an airtightness test.
  • Carry out a thermographic survey to identify leaks and assess insulation.

The net zero target

The Government has a target for the UK to reduce green house gas emissions and reach net zero carbon emissions by 2050: however, achieving this will mean dealing with the 28 million homes which are responsible for around 15% of the UK’s carbon emissions, according to the Climate Change Committee, the independent body which advises government on emissions targets. The Climate Change Committee’s lead analyst on residential buildings, Marcus Shepheard said:

High energy bills are the direct result of high wholesale prices for natural gas on global markets. The best remedy for this is to reduce, then ultimately end our dependence on gas to heat our homes and provide hot water. In the medium to long term, the best solution is to replace boilers with low-carbon alternatives, such as a heat pump, heat networks, and potentially hydrogen. In the near term, households can take steps to reduce their energy use. These include draught-proofing doors and windows, adjusting the flow temperature for condensing boilers to ensure that they actually condense, saving fuel, or lowering the temperature of a typical thermostat by 1C.

Loft insulation is a key factor in any house retrofit.

Make a roadmap for your house

Reaching the net zero target involves many challenges and will require retrofitting at a major scale. According to the Federation of Master Builders’, there are eight million lofts that need insulating, five million uninsulated cavity walls and 20 million uninsulated floors to deal with, along with requirements for fitting double glazing and new heat technologies.

Brian Berry, chief executive of the Federation of Master Builders (FMB) said:

Our homes contribute 20% of the UK total carbon emissions so unless we make them greener and more energy efficient, we won’t deliver the UK’s net zero targets. The environmental benefits of retrofitting are clear but making your home more energy efficient can also improve your health, as well as saving you money on your energy bills. At a time of rising energy process, insulating our homes makes even more sense.

It can be hard to know where to start, which is why the FMB has been leading calls for the government to back a long term `National Retrofit Strategy’. We need a comprehensive approach to making our 29 million homes greener, with a clear communications campaign that helps householders navigate their way to creating warmer homes. Getting good advice is very important, which is why seeking out a retrofit co-ordinator is a good first step as they can help give you a roadmap to all the measures you could take to make your home greener.

Energy efficient triple glazing.

 It’s important not to just think about how you heat your home, but also the home’s fabric. So that means working with a reputable builder to look at insulating walls, floors, and your roof, and finding out if your home would benefit from energy efficient windows or doors. Nearly a third of all the heat lost in an uninsulated home escapes through the walls, and 25% through the roof. A common mistake is to ignore insulation and jump straight to installing a heat pump which alone, will likely increase bills and give you a cooler home.

The whole retrofit package can be expensive, which is why the Government’s support through schemes like the Social Housing Decarbonisation Fund is important. But owner occupier householders need some support too. While the short-lived Green Homes Grant Scheme was poorly executed, the concept was correct, and the Government needs to reconsider a new version in order to help kick start the retrofit market.

Houses most likely to need retrofitting measures are older properties with solid walls, for example Victorian terraces which can be difficult to retrofit.

Whole house retrofit plan

The Royal Institute of British Architects (RIBA) senior policy and public affairs advisor, sustainability, Phoebe MacDonald, said:

Energy efficiency means using less energy to perform the same tasks. For our homes, this means using less gas, electricity or other fuels to keep them warm and comfortable. Typical interventions to improve energy efficiency include insulation in lofts and walls; draught-proofing doors, windows and floors to minimise heat loss; using superior glazing systems and changing heating methods, such as installing a heat pump.

To ensure retrofit measures work together, clients must employ a whole house retrofit plan, which includes considered individual measures that are installed at the right time. The first step should involve looking at key building information, constraints, risks and opportunities related to the building and its local context. For example, installing a heat pump (to improve the energy efficiency of a home) on the ground in a high flood risk area may result in a loss of hot water or heating should a flood occur. This understanding is integral to improving energy efficiency and making homes more resilient to climate change impacts.

Electric combi boilers are becoming a popular choice.

Fabric first approach

Improving the fabric efficiency of a home, known as taking a fabric-first approach, should also form part of a considered whole house retrofit plan. This will ensure that energy efficiency works actually improve the energy efficiency of a property and won’t add additional costs to the household. For example, this means making sure that a heat pump is only installed in a well-insulated home – the lower the flow temperature of the heat pump, the higher its efficiency. In a home without adequate insulation, the heat pump will require a higher flow temperature, which will cost more to run and have higher carbon emissions.

A RIBA architect or chartered practice can help clients set out a plan that will work for their own specific situation, not all homes are the same. Visit Find an Architect on to get started.

An air source heat pump.

Plan your retrofit project carefully

Charlie Baker, director of specialist retrofit firm Red Co-Operative said the first step when retrofitting your home is to identify what level of performance you want to achieve. He commented:

You can do the PV and battery whenever you feel like it, but a heat pump is a different ballgame; do that before you’ve done the work to reduce how much energy you need, and you could end up paying three times more than you need. Not only can the heat pump be half the price on a very energy efficient property, that efficiency enables the old radiators and pipework to work on the lower flow temperatures without having to be replaced – that’s why people stress `fabric first.’

Aim to do all the surfaces from which heat leaves and make sure they join up well to avoid the cold bridging that you otherwise get at junctions. The more efficient the surfaces get, the more influential those junctions become – they can add up to 30% of heat losses quite easily. Look for air gaps – you want your house to ventilate when you want it, not when the weather dictates it. Make it airtight, then put in a managed ventilation set-up.

Thermal insulation using mineral wool.

With top lofts, it’s cheap and easy, and allows a chance to make sure the eaves are done properly for both moisture build up and cold bridges. The biggest heat loss surface on a lot of houses is usually the walls. Solid wall insulation and external wall insulation is important, as building physics enable you to go further and you keep the thermal mass where it’s useful. If this is not possible, or you or the planners are worried about losing original architectural features, then go inside. You can make internal wall insulation look like you were hardly there.  

Cavity walls will often benefit from a top up of external wall insulation (EWI) too. If you can stretch to the windows, it’s easier to do those while you’re doing the walls; timber triple glazed windows are the optimal, most come with a 10-year paint warranty, if looked after they’ll outlast plastic, they are mostly more thermally efficient, less polluting to make and can allow larger panes of glass, so improving thermal performance and letting more light in.

Floors are usually an area worth tackling, suspended floors can often be sources of draughts and moisture. Many can be done from below to avoid disruption of lifting floorboards. However, for concrete floors in houses you’re insulating from the outside, you can get a long way by changing the insulation type and carrying the EWI all way down to the footings, stopping the heat leaving from the perimeter.”

The LETI (London Energy Transformation Initiative) Climate Emergency Retrofit Guide.

Complied by over 100 architects and engineers, this free, downloadable LETI guide is endorsed by RIBA and provides easy to understand guidance for whole house retrofits, explaining how and where to insulate: it looks at flats, terraced, semi-detached and detached houses. The guide notes that shallow refits only achieve limited results and explains how to achieve a 60-80% reduction in total energy use compared to average UK homes today. It points out the risk of poor retrofit work, explains the connection between insulation, moisture and ventilation and includes case studies. The guide recommends a whole house retrofit approach, starting with the building fabric and moving from the finite resource of fossil fuels to electricity for heating and water: it targets a 60-70% reduction in total energy consumption for the average UK home. LETI suggests that a `best practice’ level of retrofit could reduce space heating demand from around 130kWh/m2/year to 50kWh/m2/year.

Is there any financial help or grants available?

The government has committed to increasing grants for deep retrofitting from one third of the cost to half. In February the Cabinet signed off the National Home Energy Upgrade Scheme which means that it will increase grant aid to retrofit 500,000 homes and install 400,000 heat pumps by the end of the decade. The Boiler Upgrade Scheme (BUS) aims to help with the upfront costs of low carbon heating technology, and it runs from April 2022-2025. Property owners can get £5,000 off the cost and installation of an air source heat pump, biomass boiler and £6,000 off the cost and installation of a ground source heat pump. The property must have an installation capacity of up to 45kWth (which covers most homes) and a valid EPC with no outstanding requirements for loft or cavity wall insulation (unless the house has an insulation exception). While newbuild homes are not eligible, you may be if you are building your own home: grants are applied for by the installer. It may be useful to bear in mind that some lenders offer green mortgages for self-builders and renovators who carry out an energy retrofit.

Long-term approach

Clearly, there is no `one size fits all’ solution to retrofitting, and the costs of improvements can vary dramatically according to the individual house. However, as the aim is to recoup these costs in long-term savings, the homeowner must calculate timeframes for achieving that payback, balanced against having a more comfortable house to live in in the meantime.

Have I missed any important points about retrofitting?

Which of the advice here will you try first?

Let us know by leaving a comment via our contact page.

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