EnerPHit refurbishment architects: Energy efficient London houses

Architecture for London is an RIBA Chartered Practice and a specialist EnerPHit refurbishment architect, with several Certified Passivhaus Designers in our team. View our portfolio to see our recent work, or contact us on 020 3637 4236 to discuss your project.

London’s period homes pose a challenge as we aim towards the 2050 net-zero carbon emissions target. This aims to limit global heating to 1.5 degrees to avert the potentially catastrophic impacts of our planet’s warming.

Architecture for London, therefore, aims for ‘EnerPHit’ standards in our period home refurbishment projects. These are standards set by the Passivhaus Institute. The homes that we refurbish now are not likely to be improved again before 2050, so each refurbishment must achieve low-energy standards now.

There are numerous challenges in achieving these standards with our previously uninsulated and draughty Georgian, Victorian and Edwardian homes in London.

London’s historic homes

London’s historic housing stock retains a charm that, for many, provides the perfect backdrop for everyday life. Though these homes were built rapidly to fulfil the functional needs of a fast-expanding city, the design of these properties has deeply affected the way we think of what a ‘home’ is today.

 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 they perform poorly; airtightness is often almost non-existent, with typical values of around 15 air changes per hour.

 

The thermal performance ‘U-values’ of single glazing or solid masonry walls are extremely poor. We know this instinctively: we are very used to cold rooms and drafty windows, floors and fireplaces in our period properties.

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

Applying EnerPHit standards to London’s existing homes

EnerPHit is the term for the energy-focused ‘Passive House’ retrofitting of existing buildings to dramatically reduce their overall energy demand. A Passive House dwelling is a little like an insulated flask: it keeps everything inside at just the right temperature with little need for active cooling or heating.

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.

Whilst challenging, it is certainly possible to reduce a period home’s carbon footprint, while maintaining important architectural characteristics such as external materials, the relationship between façade and structure, facade composition and window detailing.

Achieving EnerPHit refurbishment certification

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.

The process can initially seem complex to homeowners, and this is where working with an experienced architect 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.

 

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.

---

Contact us now on 020 3637 4236 for a free 30-minute telephone consultation to discuss your project.

---

If you don’t have the budget to replace your original single-glazed sash windows immediately, you can plan this work for a future date.

Before any design or construction begins, an 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 architectural features.

Software modelling of a range of material and installation options and occupational patterns will help to define the proposed improvements to mitigate energy wastage, whilst avoiding potential condensation-related issues.

A London EnerPHit refurbishment case study in London

It was as a result of this process of analysis, review and testing that Architecture for London’s design for Canonbury House Extension was completed. 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.

The rear extension and internal refurbishment have been designed to employ EnerPHit measures. Each element of the building was considered, not only to address performance requirements but also to coherently knit together old and new through a strong design narrative. The existing walls relied solely on solid masonry to provide airtightness, moisture control and insulation.

Our new design insulates these walls with low embodied carbon materials, 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 altering the moisture balance in an existing wall.

The hygroscopicity and high thermal mass of the new internal finishes are also important. The walls will have an exposed natural, unpainted lime plaster finish, which also adds texture.

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.

Windows

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 are sealed with airtight tapes, preventing draughts in the construction.

Canonbury House: MVHR and renewables

To control the internal air quality, a mechanical ventilation heat recovery (MVHR) system is proposed. Systems like these efficiently remove moisture, toxins and stale air from the interior spaces.

Non-airtight buildings lose heat through draughts, bathroom extractor fans, 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.

The MVHR design and installation need to be carefully considered to minimise visual intrusion. At Canonbury House, ductwork is laid between floor joists, while the use of void spaces above secondary rooms and built-in joinery allows vents to be concealed.

The EnerPHit standard also emphasises the use of renewables to satisfy the residual energy demands after the home has been fully renovated. To bring the home towards ‘net zero’, 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.

Conclusion

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 with 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 refurbishments: FAQ