house extension in stone, islington, north london

Our existing housing stock poses a challenge as we nationally aim towards the ‘2050 net-zero’ carbon emissions target, which aims to limit global heating to 1.5 degrees. The buildings we refurbish now are not likely to be refurbished again before 2050, so they must achieve net zero standards now. This net zero goal can be achieved with an EnerPHit refurbishment strategy.

London’s Victorian housing stock

London’s historic housing stock retains a charm that for many provides the perfect backdrop for everyday life. Though these homes were built to fulfil the functional and practical needs of a city undergoing rapid expansion, their builders and first occupiers were keen to go beyond simple practicalities, drawing upon architectural ideas from the grander houses of wealthy industrialists and aristocrats.


The design of these properties has deeply affected the way we think of what a ‘home’ is today.

In fact, their ad-hoc sprawl, the result of small-scale speculation, has formed the basis of our city’s identity and communities – and left us with a patchwork of visual richness and variety.

While the picturesque qualities are to be celebrated, we can’t overlook the fact that these homes are somewhat fragile: their thermal design is antiquated and their component parts have either expired or are expiring. This means they perform poorly: our Victorian House Extension in North London, Georgian Westminster House Extension and Edwardian House Extension in Queens Park properties are an average of 2.5 times less thermally efficient than similarly sized homes built to current minimum building regulations.

To address this issue, we need to use modern construction techniques to improve the energy performance and comfort of these older properties.

Visit Architecture for London’s portfolio to see recent work, or contact us on 020 3637 4236 to discuss your project.

Applying EnerPHit standards to London’s existing homes

EnerPHit is the hybrid term for the energy focussed ‘Passive Houseretrofitting of existing buildings to dramatically reduce their overall energy demand. A Passive House dwelling is a bit like an insulated flask, which keeps everything inside at just the right temperature with little need for active cooling or heating.

Victorian house refurbishment enerphit

A low-energy retrofit proposal for a Victorian home in north London

To achieve this effect, there are five fundamental requirements;

  1. A well-insulated building envelope that retains warmth during colder months and keeps heat out during warmer months
  2. Strategically positioned, highly insulated windows to take advantage of light and heat from the sun while avoiding overheating.
  3. Efficient heat recovery and ventilation systems to provide fresh, filtered air to remove pollution (NOx, diesel particulates etc.)
  4. An airtight envelope that boosts energy efficiency while preventing draughts and moisture damage
  5. Avoidance of thermal bridges and weak points in the building envelope. This contributes to a stable internal climate and also works to minimise moisture related problems.

With careful planning, and a commitment to sustainable design, a high-performance new build home is quite achievable, but what if your home is a little more worn around the edges, with draughty doorways and damp in the downstairs WC? How can we best improve the energy performance of a Victorian home?

Indeed there are challenges, but it is certainly possible to introduce updates that reduce a home’s carbon footprint while either retaining existing components or faithfully replacing them so as to maintain important characteristics such as the relationship between façade and structure, composition and openings.


The EnerPHit approach examines the house’s environmental performance in the broadest sense, alongside the introduction of certified components (e.g. triple glazed windows) to offer the highest possible levels of performance.

Achieving EnerPHit certification

The process can initially seem complex to homeowners, and this is where working with an experienced consultant can help. EnerPHit certification can be based on either global observations, measuring functions such as ‘primary energy demand’, or on a component by component basis, assessing the performance of windows, doors, the external envelope and the ventilation systems.

Victorian house refurbishment in London to enerphit standards

A proposed refurbishment of a Victorian home in Islington by Architecture for London

Though rigorous, the EnerPHit framework embraces a holistic understanding of existing built fabric. It makes allowances for prioritising energy savings in areas where ‘easy wins’ are possible. The certification process for an EnerPHit refurbishment can also be phased, to allow works to be completed over time.

It may be that you don’t have the budget to replace your original single glazed sash windows immediately, so you can plan this work for a future date.

Before any design or building begins, a good EnerPHit designer will ensure that they understand the nuances of the building’s current condition. Data must always be at the foundation of this understanding; quantitative analysis of condensation levels and thermal imaging, but also qualitative assessments of construction technology, structural conditions, and any special features present.

Full evaluation of the gathered data alongside software modelling of a range of material and installation options and occupational patterns will help point towards specific and proven solutions to mitigate energy wastage and further fabric decay.

EnerPHit refurbishment: a case study in north London

It was as a result of a similar process of analysis, review and testing that Architecture for London’s design for Canonbury House Extension came into being. A handsome 1930’s property located in one of Islington’s 40 conservation areas, the owners approached Architecture for London with the desire to reconfigure the layout to make it better suited to the needs of modern family life.

Seizing on the refurbishment as a chance to build in long-lasting environmental and economic value, the extension and internal refurbishments have been designed to employ EnerPHit measures.

Each element that has been deployed has been carefully considered, not only to address performance requirements but also to coherently knit together old and new through a strong visual narrative. Beginning with the building envelope, the existing shell relied solely on a solid brick skin to address airtightness, moisture control and insulation. Here the design introduces materials with low embodied carbon, including wood fibre insulation and lime plaster finishes.

The woodfibre allows the existing brickwork to ‘breathe’, and while it has slightly lower thermal properties than modern synthetic equivalents it has less chance of upsetting the moisture balance in an existing wall.

The hygroscopicity and high thermal mass of the material will also offer ongoing benefits. Standard modern plaster finishes tend not to work well applied directly onto woodfibre and so instead, the walls will have an exposed natural, unpainted lime plaster finish which adds texture.

London passivhaus - view to garden

A low energy home in north London by Architecture for London

To the rear of the property, deep brick piers with lintels above are a subtle nod to the simplicity of the existing solid brick construction while creating opportunities for light to animate the open plan kitchen and dining spaces throughout the day. The materiality of the brick piers runs through into the living spaces helping to define a gradual transition from interior to exterior spaces.

As the weakest part of the building envelope, the windows and glazing are an important element of an EnerPHit home. Equally windows have a profound effect on the appearance of older properties giving clues about their history and often linking groups of buildings along a street. At Canonbury House the windows were particularly important to Architecture for London’s design proposal.

The high-performance triple glazing installed throughout will be made from FSC timber insulated frames alongside dual compression seals. These windows will ensure long-term airtightness, preventing draughts which can be a major cause of increased heating demand.

Canonbury house: MVHR and renewables

To control the internal environment, a mechanical ventilation heat recovery (MVHR) system is proposed to cover the entirety of the property. Systems like these transport unpleasant odours, moisture, microscopic toxins and stale air out of the home.

Non-air tight buildings lose heat through draughts, bathroom extractions, kitchen cooker hoods and window trickle vents. An airtight building with MVHR provides higher quality fresh air whilst also retaining almost all of the heat in the process. The MVHR’s heat exchanger transfers internal heat from outgoing air to incoming fresh external air.

Design and installation need to be carefully judged to minimise visual intrusion. At Canonbury House, ductwork is laid between floor joists, while ingenious use of void spaces above secondary rooms and built-in joinery allows the minimalist aesthetic to flow seamlessly throughout the home.

The EnerPHit standard also places emphasis on the use of renewables to satisfy the residual energy demands after the home has been fully renovated. In an attempt to bring the home towards a cumulative ‘net zero’ state, an air source heat pump (ASHP) is also proposed for the site. The ASHP will absorb heat from the air, even when external temperatures are as low as -15° C. It heats water to a higher temperature using a refrigerant system with a compressor and condenser, in the opposite manner of a household fridge. This heat then provides space heating via the underfloor heating pipework.

Once complete, Canonbury House will serve as a case study for how architects can resolve aesthetic, budgetary and sustainability drivers to deliver a refurbished home with exemplary levels of comfort and low energy use.

The desire to protect and conserve some of the most valued properties in London should be seen as consistent with an intelligent retrofit approach rather than at odds to it. Just as Victorian households took great care of the image their home presented to the street, we should strive for homes that deliver the best possible outcomes for current and future generations. To achieve this, architects must apply EnerPHit refurbishment principles when altering or extending existing homes.

To view Architecture for London’s recent projects please visit Architecture for London’s portfolio.

EnerPHit FAQ

How can we apply EnerPHit standards to London’s existing homes?

The key requirements are a well-insulated building envelope, high performance windows, an efficient heat recovery and ventilation system, an airtight envelope and avoidance of thermal bridges.

Can an EnerPHit refurbishment be phased?

Yes, it is possible to certify step-by-step retrofits with the EnerPHit Retrofit Plan.

Does the EnerPHit standard also consider renewables?

EnerPHit also places emphasis on the use of renewables to satisfy the residual energy demands after the home has been fully renovated.