A fabric-first retrofitImproving the building envelope to reduce heat loss in winter while helping to manage unwanted heat gains in summer, lowering the energy needed to maintain comfortable indoor conditions throughout the year.
Project 01
The House With The Flowery Carpet
A whole-house retrofit of our typical 1930s semi-detached home, designed around year-round comfort, lower carbon emissions and measurable performance.
We are two doctors with two young children and a dog. In October 2025, we moved from a modern 2013-built semi into a classic 1930s semi-detached house. During our first viewing, our then three-year-old daughter immediately fell in love with the bold flowery carpet running up the stairs, which is how the project acquired its name.
Behind that vintage charm was a cold, draughty and energy-inefficient home in need of serious modernisation. Rather than treating each problem in isolation, we decided to look at the house as a whole.
The plan
Our goal is to transform the house into a comfortable, healthy and low-carbon home designed around modern family life, while finding out what a comprehensive retrofit can realistically achieve in a house of this type. Comfort means more than keeping the house warm: we want indoor temperatures to remain comfortable throughout the year, warm in winter and cool in summer, with good air quality throughout.
A ground-floor extensionA wraparound addition to create a bright, open and sociable heart of the home.
A loft conversionAdding a rear dormer to create a fourth bedroom with an en-suite while bringing the roof into the upgraded thermal envelope.
Heating, cooling and ventilationDesigning heating, cooling and ventilation together to maintain comfortable temperatures and good indoor air quality throughout the year.
Generation, storage and flexible energy useCombining solar PV, battery storage, EV charging, vehicle-to-home capability and flexible tariffs so electricity can be generated, stored, imported and exported when it makes most sense.
Our priorities
Every decision we make is based on three key priorities, in this order:
Year-round comfort and healthMaintain comfortable indoor temperatures throughout the year, warm in winter and cool in summer, with fewer draughts and consistently good indoor air quality.
Lower our carbon footprintReduce the energy needed to maintain those conditions first, then meet as much of the remaining demand as practical through efficient electric systems and on-site generation.
Reduce running costsUse lower demand, efficient systems, flexible tariffs and energy storage to reduce the long-term cost of running the house without compromising comfort or indoor air quality.
The replicability
Why an ordinary house matters
Our house has nothing special about it. It is ordinary, has no unusual architectural features and was never intended to be a demonstration project. We think that is precisely what makes Project 01 a useful case study.
A common housing type
There are millions of similar houses across the UK, facing many of the same challenges around comfort, energy efficiency and decarbonisation. By starting with an ordinary existing family home rather than an architect-designed or purpose-built demonstration project, we hope the findings will be relevant well beyond this house.
Transferable lessons
Many of the challenges, compromises and decisions will be familiar to other homeowners. By documenting what we chose, why we chose it and the detailed reasoning behind our decisions, we hope others can use what we learn to make better-informed choices about their own homes, even though the exact solutions will not be right for every property.
A longitudinal study
We are recording baseline data before the main retrofit begins and will continue measuring through construction, completion and occupation. Rather than stopping when the building work is finished, we intend to share performance data for years while we live in the house, showing how the home and its systems perform over time.
The approach
Fabric first, then systems, then performance
The order matters because each layer works better when the layer beneath it is already doing its job.
01 / Fabric
An efficient building envelope
The building envelope plays a major role in determining how much energy is needed to maintain comfortable indoor conditions. Our design combines insulation, high-performance glazing, airtightness and careful junction detailing to reduce heat loss in winter while helping the house remain comfortable throughout the year.
External wall insulationCavity wall insulationParty wall insulationTriple glazingAirtightnessInsulated roof & floorsReduced thermal bridging
02 / Systems
Comfort, generation and intelligent energy management
A low-demand home allows the ASHP and MVHR to maintain comfortable indoor conditions more efficiently. Solar PV, battery storage and vehicle-to-home capability allow electricity to be generated, stored and used when it is most useful, while smart controls coordinate the different systems across the house.
ASHPMVHR14+ kWp solar PVBattery storageV2HV2GEVThree-phase supply
03 / Performance
Measure the outcome
Objective measurements allow us to test whether the completed house performs as designed. We are collecting baseline data before the main retrofit, taking measurements during construction and at completion, and will continue monitoring the house for years during occupation. The results will allow us to compare predicted and measured performance and assess the project against our three priorities: year-round comfort and health, carbon and running costs.
U-valuesHeat transfer coefficientAirtightness testingWhole-house energy monitoringIndoor temperature & humidityIndoor air qualitySystem performancePublished findings
Design targets
Design targets we can test against reality
Rather than filling this section with every number in the design model, we have selected a small set of headline targets that describe the house, the fabric and the energy system. They are useful reference points now, but the more interesting question is how closely the finished house matches them once we are living in it.
Building fabric
Design U-values
U-values describe how readily heat passes through part of the building fabric. Lower numbers indicate less heat transfer. The values below are those currently used in the August 2026 SAP design model, so they give us another set of predictions to test once the retrofit is complete.
The SAP rating, airtightness, U-values and regulated electricity demand are design-stage values from the August 2026 SAP model. The modelled electricity figure covers space heating, hot water, pumps and ventilation, and lighting before on-site PV is accounted for; it does not represent total real-world household electricity use because plug loads, cooking and EV charging are not included. The PV capacity is the quoted 28 × 540 W array, while the annual generation figure is the combined installer forecast for the four roof arrays. These are predictions rather than performance claims. We will replace assumptions with measured data as the project is completed and occupied.
Monitoring and research
Measuring the impact of the changes we make
Below are the measurements we are currently planning to carry out and share. As we learn more, speak to like-minded people and experts, and collaborate with a wider range of organisations and industries, we expect this list to grow over time.
Building fabric
QUBSmart HTCAirtightnessU-values
Energy and systems
Electricity useHeat pump SCOPSolar PV generationBattery charge / dischargeEV chargingVehicle-to-home flows
Comfort and indoor environment
Room temperature (°C)Humidity (%)CO₂PM2.5VOCsDaylight / illuminanceNoise and acousticsOverheatingComfortIndoor air quality
External conditions
External temperatureExternal humidityDaylight
Materials and carbon
Life-cycle assessmentWhole-life carbonEmbodied carbonRecycled / recyclable contentResponsible sourcing
Water
Water useWater efficiency
The questions we want to answer
Research questions shaped by our three priorities
We want to focus our research questions around the three priorities we set for the project: year-round comfort and wellbeing, carbon footprint and financial impact. Those priorities will be different for different people, and may come in a different order, but we hope to capture a broad range of reasons why people consider retrofit so that our findings can help with their own decision-making.
How well does our house maintain comfortable indoor temperatures through both winter cold and summer heat?
Has improving insulation and airtightness increased the risk of summer overheating, and how effectively can that risk be managed?
What happens to indoor air quality after our deep fabric retrofit?
Does the real-world energy data support the projections made at the design stage?
Where does modelled performance differ from the reality of living in the house?
What seasonal efficiency does our heat pump achieve in real life?
How much grid independence do we realistically achieve with solar, battery storage and V2H?
How has our carbon footprint changed?
Which interventions deliver the greatest benefit relative to their cost and complexity?
How do the financial costs and savings of different interventions compare with their effects on comfort, energy use and carbon emissions?