Energy efficiency often first announces itself through discomfort.
A front room that never quite warms up. Draughts around the windows. Condensation appearing in winter. A loft bedroom that becomes unbearably hot in summer. Or heating bills that seem out of proportion to the size of the house.
Faced with these problems, it is tempting to begin with a product. New windows, insulation, solar panels or an air source heat pump can all form part of the answer. But improving an existing home is rarely about choosing one piece of technology.
The more useful starting point is to understand how the house works as a whole.
This is particularly true of London’s Victorian and Edwardian homes. Many have been altered several times, with extensions, loft conversions and replacement windows added at different points. The original house might have solid brick walls and suspended timber floors, while a later extension has cavity walls, concrete floors and a completely different thermal performance.
A successful energy-efficient renovation needs to respond to that mixture rather than applying the same solution everywhere.
What does an energy-efficient home feel like?
Energy performance is usually discussed through calculations, bills and insulation values. These measurements matter, but they are not the only way people experience a better-performing home.
A well-designed low-energy home should feel more comfortable.
Temperatures remain steadier throughout the day. Internal wall surfaces feel warmer. Draughts are reduced. Bedrooms are less likely to overheat. The heating does not need to be switched on and off constantly to compensate for rapid heat loss.
Good ventilation should also improve air quality and manage moisture without making the house feel cold.
These changes can have a greater effect on everyday life than the energy figures alone suggest. A previously unused room becomes somewhere people want to spend time. A kitchen feels comfortable on a winter morning. The loft remains usable during a period of hot weather.
The objective is not simply to reduce the amount of energy a house consumes. It is to use less energy while making the home more pleasant to live in.
Where is heat commonly lost in a London home?
Heat can escape through almost every part of a building, although the balance varies considerably from one house to another.
Roofs and lofts are often an obvious source of heat loss, particularly where insulation is thin, badly installed or interrupted around joists and roof structures.
External walls can account for another significant proportion. Most Victorian terraces were built with solid brick walls rather than modern insulated cavities, although the construction may change around rear additions and later extensions.
Suspended timber floors can allow cold air to move beneath the house and enter through gaps between boards, skirtings and service penetrations.
Windows and external doors may lose heat through the glass, frames or draughts around their edges. Poor installation can undermine even a relatively high-performance window.
There is also uncontrolled air leakage. Warm air escapes through gaps around floors, ceilings, loft hatches, pipework, chimneys and junctions between old and new construction.
This is why a whole-house assessment is valuable. A house that appears to need new windows may have a much greater problem at roof level. Another may have reasonable insulation but suffer from uncontrolled draughts and poorly performing heating controls.
Understanding the existing building allows time and budget to be directed towards the improvements that will make the greatest difference.
Begin with the building fabric
A fabric-first approach means improving the parts of the building that separate inside from outside before relying heavily on mechanical systems.
The building fabric includes the roof, walls, floors, windows and doors. Improving these elements reduces the amount of heat needed to keep the house comfortable.
This has several benefits.
Heating systems can run more efficiently. Rooms remain warm for longer after the heating switches off. Cold internal surfaces are reduced. In some cases, the calculated heating demand becomes low enough to allow a smaller heat pump or lower-temperature heating system.
Fabric improvements can also last for decades. Heating technology will continue to evolve, but a carefully insulated wall or roof should continue to perform regardless of how the home is heated in future.
That does not mean every surface must be insulated to the maximum technically possible. Space, cost, heritage, moisture and disruption all need to be considered.
Good retrofit design is often about finding the most appropriate balance rather than simply adding the greatest thickness of insulation.
(read more about the fabric-first approach)
Why period homes require a more nuanced approach
Traditional London houses behave differently from modern buildings.
Many were built with solid brick walls, lime mortar and lime plaster. These materials can absorb and release a certain amount of moisture. The suspended floors and open chimneys also created a considerable level of natural air movement, even if much of it was uncontrolled.
Problems can arise when modern impermeable materials are added without understanding this original construction. Moisture may become trapped within a wall or timber floor, increasing the risk of damp, mould or decay.
This does not mean Victorian houses should be left cold and inefficient. They can often be improved significantly. The materials and details simply need to suit the building.
At The Judd, our low-energy renovation of a Victorian terrace in Tottenham, the external walls were insulated internally using cork and finished with lime render. This created an insulating layer while maintaining a vapour-permeable wall build-up capable of managing moisture.
Other houses may require a different solution. Existing damp, external exposure, decorative plasterwork, room dimensions and the condition of the brickwork can all influence the design.
Listed status or a Conservation Area location may also affect what can be changed and which permissions are needed.
For architects working with period homes in London, the challenge is to improve performance without losing the qualities that made the house valuable in the first place.
(read more about improving comfort in a London period home)
Insulation, airtightness and ventilation must work together
Insulation slows the movement of heat through the building fabric. Airtightness reduces the amount of warm air escaping through unintended gaps.
Both can make an enormous difference, but neither should be considered in isolation.
Older homes often rely heavily on accidental ventilation. Air enters through gaps in floors, windows, doors and chimneys. This can make the house cold, but it also helps remove moisture.
Once those gaps are reduced, the home needs a more deliberate ventilation strategy.
That might involve well-designed background ventilation and extract fans. In a more comprehensive refurbishment, mechanical ventilation with heat recovery, commonly known as MVHR, may be appropriate.
MVHR extracts stale, humid air from kitchens, bathrooms and utility spaces while supplying fresh air to living rooms and bedrooms. Heat from the outgoing air is transferred to the incoming air, reducing the amount of warmth lost through ventilation.
It can be very effective, but it requires space for ductwork and careful installation. It is usually easiest to incorporate during a whole-house renovation rather than adding it once the finishes are complete.
The correct approach depends on the building, the scale of the work and how the occupants live. The essential point is that reducing draughts should be accompanied by a reliable way of maintaining healthy air quality and controlling moisture.
Should windows be replaced?
New windows can reduce draughts, improve comfort and help control external noise. They are also one of the most visible changes to a period home, so performance and appearance need to be considered together.
Complete replacement is not always the only option.
Existing timber windows may be capable of repair, draught-proofing or discreet secondary glazing. In other cases, high-performance double or triple glazing may be appropriate.
The glass is only part of the equation. Frame materials, opening sections, installation details and the junction between the frame and wall all affect performance.
Glazing also influences summer comfort. Large areas of unshaded glass can introduce substantial solar heat, particularly in lofts and south- or west-facing rooms.
A good window strategy therefore considers winter heat loss, daylight, ventilation, noise, architectural character and summer overheating at the same time.
When does an air source heat pump make sense?
An air source heat pump takes low-temperature heat from the outside air and uses electricity to raise it to a useful temperature for heating and hot water.
Heat pumps can work successfully in renovated period properties, but they need to be designed around the building rather than treated as a direct replacement for a gas boiler.
The first step is an accurate room-by-room heat-loss calculation. This establishes how much heat the home needs and whether existing radiators are large enough to provide it at lower water temperatures.
In some homes, radiators need to be replaced with larger models. In others, underfloor heating may form part of the design. Improving insulation and airtightness can reduce the scale of these changes.
The external unit also needs an appropriate location. Noise, air movement, maintenance access, garden design and nearby neighbours should all be considered.
A heat pump fitted to a poorly understood building may be expensive to run or fail to provide consistent comfort. A well-designed system in a properly assessed home can deliver stable temperatures with no on-site fossil-fuel combustion.
At Olive, our completed project in Stoke Newington, the air source heat pump works alongside a replacement extension, improved building fabric and carefully considered glazing. The clients describe the result not through the technology itself, but through the evenness of the temperature and the way the house now remains comfortably warm.
That is usually the better measure of success.
(see how an air source heat pump performs in a completed family home)
Where do solar panels and batteries fit?
Solar photovoltaic panels generate electricity, which can be used in the home, stored in a battery or exported to the grid.
They can work particularly well alongside an air source heat pump, although solar generation is highest during brighter periods when heating demand may be lower.
A battery can increase the proportion of generated electricity used within the home and may also allow electricity to be purchased and stored at cheaper times, depending on the tariff.
These technologies can reduce reliance on grid electricity, but they are not substitutes for improving the building itself.
A poorly insulated and draughty home does not become comfortable simply because solar panels have been installed on the roof. In most cases, reducing energy demand and generating cleaner energy should be considered as complementary parts of the same strategy.
Energy efficiency is not only about winter
London homes increasingly need to cope with periods of hot weather as well as cold winters.
Lofts are particularly vulnerable. Lightweight construction, large rooflights and thin foil-backed insulation can result in rapid temperature increases during sunny days.
The position and size of glazing, external shading, cross-ventilation and the ability to release heat at night all affect summer comfort.
Insulation materials also behave differently. Some dense materials can absorb and delay heat more effectively than lightweight alternatives, helping to moderate internal temperatures across the day.
This requires thought at the design stage. Adding air conditioning later may address the symptom, but it does not resolve the reasons a room is overheating.
Our separate guide, Designing Homes to Stay Naturally Cool, looks in more detail at glazing, shading, ventilation, thermal mass and the design of loft spaces.
(read more on how to reduce overheating naturally)
In what order should energy improvements be considered?
Every house is different, but a sensible process often follows a broad sequence.
Start by understanding the building. Review the construction, existing insulation, heating use, ventilation, moisture and areas of discomfort.
Deal with water ingress, damp and essential repairs before concealing the fabric behind new finishes.
Identify where heat is being lost and develop a coordinated insulation and airtightness strategy.
Design the ventilation approach alongside the fabric improvements.
Review the windows, external doors and glazing in the context of both winter and summer performance.
Recalculate the reduced heating demand before selecting a replacement heating system.
Consider solar panels, batteries and other renewable technologies once the likely electrical demand is understood.
Return to the house after occupation and compare the design assumptions with the way it actually performs.
This work does not always need to happen at once. Some homeowners need to improve their property in stages.
The important thing is to have a long-term plan. A new boiler, loft conversion or replacement window should not prevent a better whole-house solution several years later.
Where possible, it is often efficient to coordinate energy improvements with an extension or major refurbishment. Floors, walls and ceilings are already being opened, making it easier to improve awkward junctions and integrate ventilation, heating and electrical systems.
The Judd: a deep retrofit in practice
The Judd is the home of Patricia and Gwen, a retired couple who had lived in their Victorian terrace in Tottenham for more than 20 years.
Their brief was not simply to reduce energy use. They wanted a home that felt distinctive, generous and personal, with an architectural language influenced by the American artist Donald Judd.
The project became an opportunity to show that strong interiors and serious building performance do not need to pull in different directions.
Rather than adding a large ground-floor extension, we retained the existing footprint and made a series of precise spatial changes. Parts of the house were opened up, daylight was drawn deeper into the plan and the loft was extended to create an additional bedroom.
All external walls, including the side wall of the previous rear addition, were retained and upgraded. This reduced the amount of demolition and new material required.
Cork insulation and lime render were introduced internally to improve the thermal performance of the solid walls while managing moisture appropriately.
The house was made more airtight, with ventilation considered as part of the wider strategy. An air source heat pump replaced the gas heating system, and photovoltaic panels were added to the roof.
Existing rooflights and sanitaryware were carefully removed and reinstalled in new locations where they could be used within the revised design.
The result is a home in which environmental performance sits quietly behind the architecture. Colour, proportion, art and material character remain central to the experience of the rooms.
(explore The Judd low-energy renovation)
What did the measured results show?
Before the renovation, the house had three bedrooms, a gross internal area of 111 square metres and two occupants.
After the work, it had four bedrooms and a gross internal area of 138 square metres, an increase of approximately 20 per cent.
Annual purchased gas and electricity before the renovation totalled 21,765 kWh, equivalent to approximately 196 kWh per square metre.
Following the renovation, purchased grid electricity was recorded at 7,190 kWh, equivalent to approximately 52 kWh per square metre.
This represents a reduction of approximately 67 per cent in purchased annual energy and approximately 74 per cent when measured against the increased floor area.
The house also no longer burns gas on site. Heating and hot water are supplied electrically through the air source heat pump, with part of the electricity demand supported by the solar panels.
These figures need to be understood in context. They describe one house, occupied by the same two people before and after the work. They should not be treated as a promise that every Victorian renovation will produce an identical saving.
Weather, occupancy, internal temperatures, energy tariffs and the condition of the original building all influence the outcome.
What The Judd does demonstrate is that a coordinated approach can substantially improve a home’s measured performance, even while increasing its size and creating a more ambitious architectural interior.
Where should you start?
For most homeowners, the first step should not be ordering windows or choosing a heat pump.
It should be developing a clear understanding of the existing house, the problems that need to be addressed and the way different improvements will affect one another.
A good energy strategy is rarely the result of one dramatic intervention. It comes from a series of carefully coordinated decisions: insulating the right places, reducing unintended air leakage, managing moisture, providing fresh air, selecting appropriate glazing and designing a heating system around the improved building.
Period homes can be challenging, but they are also remarkably adaptable. With careful design, they can retain their character while becoming warmer, healthier, more comfortable and significantly less energy-intensive.
If you are considering an energy-efficient renovation, extension or whole-house retrofit in London or the South East, we would be happy to discuss the opportunities presented by your home and help establish the most appropriate place to begin.
(read about a low-energy retrofit of a significant mid-century home we are developing)
Frequently Asked Questions
What is the first step in making a house more energy efficient?
Begin by assessing the existing building rather than selecting an individual product. Look at the roof, walls, floors, windows, airtightness, ventilation, heating system and any existing damp or maintenance issues. This helps identify which improvements are likely to make the greatest difference and how they should be sequenced.
What is a fabric-first renovation?
A fabric-first renovation prioritises improvements to the roof, walls, floors, windows, doors and airtightness of a home. By reducing heat loss through the building envelope, the amount of energy needed for heating is reduced before new heating or renewable-energy systems are designed.
Can a Victorian house be insulated without causing damp?
Yes, but the insulation strategy must respond to the construction and condition of the existing building. Traditional solid walls often need vapour-permeable materials and carefully detailed junctions to manage moisture. Existing damp, leaks or defective pointing should be addressed before insulation is installed.
Do heat pumps work in period homes?
Heat pumps can work well in period properties when they are properly designed. The building’s heat loss should be calculated, and radiators or underfloor heating need to be sized for lower water temperatures. Fabric improvements can reduce heating demand and help the system operate more efficiently.
Should windows be replaced before installing a heat pump?
Not necessarily, although window performance should be included in the heat-loss calculation. Repair, draught-proofing, secondary glazing or replacement windows may each be appropriate depending on the property. The heating system should be designed around the performance the completed home is expected to achieve.
Is MVHR suitable for an existing house?
MVHR can be suitable for a comprehensively renovated existing home, particularly where airtightness is being significantly improved. It requires space for ductwork and careful design, so it is usually easier to install during a major refurbishment. Simpler ventilation strategies may be more appropriate for smaller or phased projects.
Can adding insulation make a house overheat?
Insulation does not automatically cause overheating, but summer performance needs to be considered alongside winter heat loss. Glazing, shading, ventilation, roof construction, thermal mass and the type of insulation all affect how quickly a room heats up and how easily that heat can escape.
What is a deep retrofit?
A deep retrofit is a comprehensive improvement to an existing building that significantly reduces energy demand. It may include insulation, airtightness, ventilation, improved glazing, low-carbon heating and renewable energy, usually coordinated as part of a whole-house strategy.
Is it better to improve a home all at once or in stages?
A whole-house renovation allows systems and construction details to be coordinated more easily, but staged improvement can also work. The key is to establish a long-term strategy so that early decisions do not make later improvements more difficult or expensive.
The new air source heat pump in the garden at The Judd
Breathable cork insulation and lime render lining the inside face of all external walls
Visit the Ofgem website and read about average household energy usage.
