meeting reports

Report of public meeting 15 May 2025

CA-WN Exchange

21 May 2025 • 14 min read

May’s speaker was Natasha Ginks. Natasha is a qualified Retrofit Co-ordinator with considerable practical experience as well as qualifications in the field of home retrofit. Natasha’s presentation was titled "Where to start with retrofit" - the slides are available to download¹ and a recording of the meeting is on our YouTube channel².

Apologies: Alexina Cassidy, Clare Slater, Jonathan Harris, Maria Lee, Peter Nalder
Present: Sumiya Afrin, Alison Barlow, Leonie Beale, David Garlick, James Hadfield, Hilary Haynes, Patsy Hollingum, Richard Hollingum, Rupert Knowles, Mike Longman, Mick Lorkins, Harry Mellor, Clare Robertson-Marriott, Jane Wood

My retrofit journey

Natasha’s career in retrofit started when she studied for an MSc in Climate Change and Sustainability and became very interested in buildings and how to reduce their emissions, making them cheaper to run and healthier to live in. She then moved to Oxfordshire, bought a very old house that needed a lot of work, and decided to focus on sustainability and get the house off fossil fuels. The project took about 6 years, and they now have a lovely old house which is warm, heated by a heat pump, has lots of solar and is a very comfortable living environment.
She started the Renovate Green blog in 2013/14 to share her journey and what she was learning. The blog is still on her website³ – she doesn’t write blogs any more but still gets a lot of feedback.

Having completed her own project Natasha trained as a retrofit co-ordinator in 2017/18. This was a new role then, introduced off the back of PAS 2035⁴, a retrofit standard written by architects and surveyors. A retrofit co-ordinator is trained in retrofit, is not necessarily an architect (though some are) but has good knowledge of retrofit and how buildings work. Natasha has gone on to do additional training in traditional buildings and how to retrofit them, which is very different to modern buildings. She set up a consultancy and worked on her own for a few years. When Cosy Homes Oxfordshire (CHO)⁵ started up with the help of government funding she joined forces with them to roll out retrofit across Oxfordshire.

Cosy Homes Oxfordshire (CHO)

CHO is a collaboration between Low Carbon Hub⁶ (LCH) and RetrofitWorks⁷(RW). LCH is a community owned renewable energy co-operative; RW is a not for profit national organisation which focuses on improving energy efficiency in buildings. The objective of CHO is to accelerate the speed and quality of domestic retrofit in Oxfordshire. It primarily works with people who can afford to pay for their own improvements rather than on big social funded projects, though they do work with local authorities.

There are several active community and advocacy groups in Oxfordshire, which are very important in helping CHO to reach people. LCH has people with strong links to community groups and they have worked together to develop programmes designed to encourage people to do retrofit.

CHO primarily has an advisory role throughout the whole retrofit process, sitting between the householder and the contractor. CHO is completely independent and doesn’t have contractors on its books, but the contractors they recommend have all been vetted by RW. CHO also offers training to contractors on various aspects of retrofit and all are trained to meet PAS 2035 standards.

What is retrofit?

Adding ‘something’ to your home that wasn’t there when it was built. This can be to the outside, the interior, also new building services such as heating, ventilation and cooling, insulation, new windows etc.

CHO follow a Fabric First approach. The principle behind this is that getting homes off fossil fuels means moving to electricity, for which the only currently viable option is heat pumps. The price of electricity is 3-4 times higher than gas, so to switch to electric heating affordably it’s essential to make sure the heat pump can convert electricity very efficiently into heat and that the heat demand of the house is lower than it is when heated by gas. Otherwise the fuel bills will be crippling.

CHO always look to see how the building fabric will be addressed to bring down heat demand first, and installation of renewables/more efficient heating comes afterwards. Plenty of homes are already efficient enough to run a heat pump effectively, but it is important to properly assess this.

Where CHO is different to some other organisations is that they are very focused on using sustainable materials (i.e. natural). They do use rockwool (mineral wool) insulation which has quite high embodied carbon but is made from sand and rock, not plastic-based. Most of their work uses materials such as wood fibre, cork insulation, lime plasters. This is partly because there are a lot of traditional buildings in Oxfordshire.

Why are people interested in doing retrofit?

In the market CHO work in people are mostly spending their own money with possibly some small grants. The primary reasons for wanting to do retrofit are:

Reduce carbon emissions
Improve EPC rating e.g. ready for selling, as a better EPC can improve the selling price. This wasn’t the case 5 years ago but now the whole concept of retrofit is more widely understood.
Big rental market in Oxfordshire and with increased restrictions on landlords they are keen to make sure properties are up to the required standards. Many are also good landlords who don’t want tenants to be living in cold hard-to-heat properties.
Reduce energy consumption and bills
Want a more comfortable home
Prevent overheating in the summer – many people have loft rooms which might be office space or bedrooms which if not properly insulated overheat badly in summer
Improve indoor air quality. This is top of a lot of lists now especially post Covid and with media coverage which made people aware of the importance of ventilation in preventing damp and mould.

Trigger points - when do people decide to do the work?

Retrofit can be really disruptive and expensive, so there is usually a specific reason for doing it:

Moving home or extending. The extension will be built to latest building regulations so will be nice and warm - people want the rest of the house to be the same
New baby
Elderly relative moves in
Old boiler fails, and don’t want to put in a new gas boiler
Neighbours doing it – all the research and much of what CHO do demonstrates that people don’t like doing retrofit as an early adopter. They want to see it tried and tested and if a couple of people on a street have done it, it is much more likely that others will follow as they don’t want to be left behind either.
Government and local authority grants when on offer.

The retrofit journey

The process that CHO uses consists of three stages:

Consultancy

Plan Builder app gives you an idea about what you could do
Call from retrofit co-ordinator to discuss requirements
Send out surveyor to get information about the house, measurements, insulation levels etc.
Information is sent to the retrofit co-ordinator who puts this on a software system from a company called Cotality – this calculates the heat demand of the house, estimates the fuel bills and the emissions and then works out what retrofit measures could be done and what the effect would be. CHO use the software output as the starting point to produce a Whole House Plan, but every house plan is bespoke and they go through it in lots of detail to make sure proposals fit with the house and the aspirations of the householder.

Technical

Some people don’t want to go any further after receiving the plan, but if they do choose to proceed CHO provides a technical specification and cost estimates. The estimates are based on previous work with known contractors so are more accurate than those in the software.

Installs

The householder asks CHO to get quotes from contractors.
The contract is signed between the householder and the contractor; CHO is just an adviser.
The retrofit co-ordinator or another representative of CHO goes to the property and checks everything has been done correctly.
The work is signed off by the retrofit co-ordinator.

Case studies

1970s 3 storey terrace house in Headington
This home had 3 occupants – they wanted to reduce emissions and improve the ventilation. They already had solar panels and a battery. Their budget was c£20,000.
Prior to work starting the house had:

Low pitched roof with 100mm insulation
Cavity walls which had not been filled, plus a lot of windows.
Bathroom extractor which didn’t work well and vented into the loft causing mould and condensation in the loft
Most windows were pre-2002. This is an important date as lots of developments in window design after that. There were no trickle vents and the vent fans didn’t work, so mould was forming
Not very well insulated hot water tank

The software report showed:

High bills
Fairly good energy efficiency rating even though the house performed quite badly in terms of comfort. This was because of the solar panels which tend to push up the EPC rating. Hence solar is popular with landlords as it isn’t disruptive to tenants.
The software produces a graph showing which elements of the property are using the most energy. Highest consumption was hot water and then heating. Boiler inefficiency and heat losses through walls also quite high.

Heat demand = The energy required by the property to heat it divided by the floor area (kWh/m²)

Heat demand can be used to compare houses of different sizes. Note all software figures are estimates not based on actual fuel bills, it uses assumptions about the number of people and the temperature they want to live at.
If heat demand is calculated to be 90 or below the home will generally work with a heat pump quite efficiently without being too expensive to run.

Retrofit proposal to client
The analysis shows the potential effect on bills and heat demand of each of the measures.

Phase 1

Cavity wall insulation
Increase loft insulation to 300mm
Replace older windows
Add ventilation

Phase 2

External wall insulation

Phase 3

Heat pump with new hot water tank and some upgraded radiators

The householder went ahead with all Phase 1 measures but did not go for the external wall insulation as it was expensive, with limited impact on top of the cavity wall insulation. Also as the property is a terraced house it would have looked different to its neighbours.
They did go with Phase 3 and put in a heat pump and new hot water tank.

Traditional house case study
Three common retrofit measures that CHO use for older, traditionally-built homes.

Suspended timber floor insulation
This is illustrated on the slides with a diagram from Ecological Building Systems⁸, a company that supplies sustainable retrofit materials but also provides training and free step by step guides.

Installation process:

Lift up floor covering to expose floor joists, ensure minimum 150mm between the bottom of the joist and the ground, plus good cross ventilation.
Membrane is placed between and over the joists, secured with battens.
Add insulation, either mineral wool or wood fibre. Natasha doesn’t recommend sheep’s wool – despite being impregnated with Borax, after about 10 years the material is vulnerable to moths. She has personal experience of dealing with this as she has wool insulation in her own loft. There is now a new type of wool insulation which is treated differently but Borax flakes off over time.
A second moisture and airtightness membrane is added
Lay down the floor covering.

This is quite an invasive and disruptive process. Usually under floors there is a lot of rubble that has to be dug out, plus sometimes crooked floor joists as well as a lot of pipework and so on that has to be worked around.

Generally it requires much more work than you think!

The case study house did this and put in underfloor heating too, which is worthwhile if you are pulling the floors up as it works well with a heat pump.

Triple glazed timber windows
There are regulations relating to work on buildings that are listed or in conservation areas – Oxford is very strict about applying these so windows have to look the same as the originals. CHO knows a couple of good manufacturers who make new triple glazed windows very similar to the original ones.

In order to achieve a really high performing window it must be installed properly. This is the tricky part as there would often have been a traditional sash window with gaps and shafts behind it. A lot of work has to be done to make sure heat does not leak from around the window. There are good expanding tapes on the market, which are airtight, waterproof and windproof. CHO also use air tightness tapes on the inside. It’s extremely important to avoid creating a thermal bridge which will cause a cold spot and therefore mould.

Room in roof insulation
Lots of Victorian properties (and also modern ones) have rooms in the roof which can be really cold. People want to make sure these rooms are fully usable so want them properly insulated against cold in winter and overheating in summer.
The system illustrated on the slides uses Steico wood fibre insulation. Again this is a fairly invasive process:

Start by stripping off plaster to expose the rafters
Install 50mm of flexible wood fibre between the joists, then a less flexible product in 50mm increments
Then a vapour control membrane. With roof rooms, all the moisture from the house ends up under the roof so it needs to be able to move through the fabric of the building. If you use plastic PIR insulation such as Celotex it is not permeable, so moisture can collect behind the rafters resulting in mould. It’s crucial to have a ventilation gap between the rafters and roofing membranes and a ventilation pathway allowing moisture to be wicked away through natural air movement.

Retrofit going forward

Tricky market currently due to economic uncertainty and governments backing down a little on their net zero commitments. However there is still a lot of interest in retrofit for other reasons.

Grants are all around heat pumps rather than insulation which is quite short sighted. Some grants are available in social housing and for people in receipt of benefits, but none currently for people in the ‘able to pay’ market.
There are finance options such as green mortgages and loans based on energy efficiency measures but generally research shows that people remain sceptical about taking out finance to pay for retrofit.

There is lots of good information available online and several organisations in different areas offering a similar service to CHO.

Contractors are skilling up now, this used to be a very weak point 3 years ago but that is changing. The Net Zero Skills Hub in Abingdon⁹ trains school leavers to do retrofit building works properly.

There is driving force coming from local authorities and some town councils too. Oxford City Council have been great at getting funding for retrofit.

CHO has launched the House Like Mine project¹⁰ with Oxford City Council. It took 12 of the most common house types in Oxford, analysed each one and produced a lot of material about the house demonstrating how to add solar, insulation etc. and what this would mean in terms of energy efficiency. These are free to all householders with a similar property, and are great for those who can’t afford the £300-£500 for a bespoke whole house plan.

Q&A

My family members have a mid-terrace Victorian house. They are interested in doing retrofit but worried it will be really expensive.
Look at House Like Mine for the case studies which include a Victorian terrace. When planning work always try to work in stages and build stages around particular budgets.

The Whole House Plan ensures things are done in an order which avoids undoing previous work. Most clients do not have lots of money to spend at once - people might ask ‘what can I do for £6k?’ and CHO can devise a plan. It doesn’t always need to be expensive and it doesn’t all need to be done at the same time. Cavity and loft insulation don’t cost the earth for example; internal insulation can be done room by room and there are some cheaper options for suspended timber floors.

What’s the cost of getting an assessment completed?
Based on the size of property - for 2-3 bedrooms it would be £300-£400, for a 5-bed it would be c£600. The software enables analysis relatively cheaply, albeit with compromises in terms of using estimates and assumptions. With other packages which are more detailed and look at actual data a plan would cost c£3000, which most people aren’t able or prepared to spend.

CHO surveyors are also qualified to do EPC assessments so can lodge an EPC certificate as well as doing the detailed survey. Useful if this is one of the motivations for doing the work.

Floor insulation – is that a suspended ground floor, rather than between floors?
Yes, but if doing a very deep retrofit where everything is being stripped back, it is quite common also to do intermediary floors to restrict heat losses where joists go into the wall and to provide sound insulation as well.

Do you advocate cheaper measures too?
Yes, very much in favour of these. When writing Whole House Plans Natasha always advocates things like thicker curtains and shutters. CHO often do thermal image surveys where the client isn’t sure where their money would be best spent. It’s amazing the difference even quite a thin blind pulled down over a window can make to heat loss. Old fashioned measures such as shutting doors, using draught excluders and putting strips of cork between floorboards in suspended timber floors are very effective. It’s worth going around the house to find draughts and gaps which can be sealed off. These are DIY tasks as not the sort of things contractors want to do unless they are already working on the property.

Trickle vents on windows – isn’t that making the windows leaky?
Yes, trickle vents are very hard to explain as it feels intuitively wrong! The latest update to building regulations means that unless you have a properly installed mechanical ventilation system in your house you are required to have trickle vents on all new windows. This is because there are so many problems caused by lack of ventilation. Ventilation works by extracting stale air and then replacing it with fresh air - this is the side of the equation that was not being met in some homes when insulation was improved.

Trickle vents are sized so that there is a controlled amount of ventilation coming in - they can be shut off but shouldn’t be. Some now can be programmed to measure the humidity level and will open and close accordingly. Ventilation systems have developed hugely in the last few years. Trickle vents can now talk to extractor fans etc. They are needed; it does feel a bit mad to cut a hole in a well performing window, but the point is that it is controlled.

Do you fit air to air heat pumps (as opposed to air to water where the water is heated to supply radiators)?
Sometimes. Natasha is not an expert on these but they can be pretty good in open spaces, less so if the property has lots of smaller rooms. They are being developed and becoming better. Air to air heat pumps don’t qualify for the boiler upgrade grant which may be one reason they are not so common in the UK. They are very much used in other countries including Germany and Sweden. Air to air is good for small flats and much cheaper to install than air to water heat pumps especially if the home already has electric heaters installed.

Can you tell us a bit more about the structure of CHO and how it is set up?
Natasha is an independent consultant (by choice) but CHO also has 3 inhouse retrofit co-ordinators; these are employed by RetrofitWorks rather than CHO. The CHO team also includes a project lead and two admin and marketing staff. Low Carbon Hub has a fairly big team too and much of the CHO marketing is done through them. LCH is completely separate, they are a very successful community owned renewables group. CHO sits underneath RW and is closely interlinked with it.

CHO is Oxfordshire based – there are similar organisations in other areas (see the final slide of Natasha’s presentation for some examples). Ecofurb and Furbnow are private companies and more national. Local schemes tend to work better as this enables building up relationships with local contractors who understand the local housing and how it is built.

It is worth going to your local authority as they may have an account with Cotality already. LAs have to work out emissions for their own buildings and many use Cotality for this. It’s not too hard to learn how to use the software and if you can find good energy assessors who really know how to survey a house properly, you can get some homes surveyed and upload that data to Cotality.

There will be independent retrofit co-ordinators in West Northamptonshire that know how to use this software already. Look at the archetype homes mentioned earlier, take a common house type and survey a couple, then see what interest you get.

AOB

CA-WN is running another free Carbon Literacy course starting 2 June
Another chance to hear about retrofit - on Wednesday 21 May, Harborough Climate Action have an event about Family Home Retrofit, with Sarah van der Walt, energy consultant to new house builders.
Saturday 24 May - Festival of Nature in Kettering, put on by Kettering Nature Group. Free, great for families.

Details on our What’s On page¹¹