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We are currently facing the dual dilemmas of a climate emergency and widespread species extinction. Our existing homes in the UK consume vast amounts of energy in the form of fossil fuels. How can homeowners begin to address these issues? This article provides sustainable house refurbishment ideas.

The UK has committed to achieving net-zero emissions by 2050, and the built environment plays a significant role in that. It is responsible for around a quarter of our total greenhouse gas emissions. The homes that we retrofit now won’t be improved again before 2050, so it’s crucial that we aim for sustainable house refurbishments to the stringent Passivhaus EnerPHit standards.

We believe that the key to achieving these standards for all our homes across London and throughout the UK is striking the correct balance between sustainability, budget, and aesthetics.

A sustainable house refurbishment in north London

Low Energy House is located in Edwardian suburbia, near Muswell Hill in north London. The home underwent a loft conversion, rear extension, and retrofit. We also removed internal walls on the ground floor to create a modern, open-plan living space and allow natural light to be spread more effectively. It’s a typical London terraced house and the project had a relatively modest budget of about £250,000.

Ground floor of Low Energy House, Muswell Hill

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A dark and damp property

The house, as bought, was a very typical uninsulated brickwork Edwardian construction. There were several issues such as the front of the house being covered with a non-breathable cement render, which resulted in damp problems. There were still original single-glazed windows, and generally, the interiors were dated and in poor condition.

There were also more severe problems with the house. Some rooms faced directly north, resulting in very low levels of natural light, something we wanted to address. A typical Edwardian ventilation detail of a simple large opening in the external wall resulted in moisture ingress and condensation problems.

For more information about working with Architecture for London, please contact us on 020 3637 4236 to discuss your project, or visit our architecture project portfolio to see a selection of our previous sustainable refurbishment projects.

The single-glazed windows caused condensation to form, leading to mold growth along the window sill. Another issue was the original rear reception room at ground level. It was almost unusable due to a 20th Century kitchen addition that blocked nearly all natural light.

Historical damp-proofing work led to significant damage. A non-breathable, cement-based damp-proofing plaster had been added internally to a metre above the finished floor level on both the ground floor and the first floor. It trapped moisture within the wall, pushing it upwards and deteriorating the lime plaster line at that level. The plaster was damp and blown, and the face of the brickwork was so damp that it came off as the plaster was removed. A variety of unhealthy mould species was thriving in the construction gaps!

“It’s impossible to exaggerate the awesome nature of the challenge we face. Global warming is already a prime factor in destroying species at a rate not seen for 65 million years” – Noam Chomsky

Structure of Low Energy House

It’s important to remember that approximately 50% of a building’s embodied energy (the energy used in the extraction, process, delivery and installation of materials in a construction project) typically resides in its structure. Therefore, in a sustainable refurbishment project we should try and minimise the amount of high embodied energy materials like steel and concrete used in any proposed new structure.

On the ground floor, we managed to decrease the usage of steel by retaining masonry nib walls. Instead of opening up the entire wall to create a completely open-plan space, we retained a portion of the wall, which provided us with lateral stability. This meant we did not have to construct a large steel box frame, but only needed a single steel support to carry the load from above.

In the rear extension, we avoided pouring a continuous concrete slab. Instead, we used strip foundations and extended the suspended timber floor into the new extension, which saved a considerable amount of concrete.

The loft conversion was built with timber beams and posts, thereby avoiding any substantial use of steel. A single flitch beam in the floor of the loft was the only steel component required.


First floor bedroom at Low Energy House, Muswell Hill

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Sustainable refurbishment materials

In terms of embodied energy within finishes, our strategy was to minimise the use of cement-based and plastic-based building products. Instead, we chose sustainable materials like lime plaster, timber and natural stone tiles instead of ceramics and concrete.

Insulation and heating

The ‘energy in use’ component, which consists of heating, cooling, ventilation, power requirements, lighting, appliances, and hot water, can also be significantly altered. One of the most substantial changes we can make pertains to the energy needed to heat a building. We applied Passive House principles, which include insulation, airtightness, and mechanical ventilation with heat recovery (MVHR). We aimed for Passive House fabric U-values of 0.15 everywhere, which we achieved except for the front facade.

The front facade was insulated internally with wood fibre to maintain the external Edwardian character, while the rest of the house was insulated externally for better performance. The internal walls were finished with lime plaster.

In the loft conversion, we had to insulate internally along the party wall because the neighbouring loft hadn’t been converted. We also positioned the MVHR unit in the loft. To facilitate the MVHR ductwork running down through the lower floors, we added a curve in the new stair’s plan, creating a small void.

“There are disastrous consequences for wildlife if human-caused emissions raise global temperatures up to 4.4 degrees Celsius, which is currently the trajectory we’re heading towards. Extreme heat could endanger 40% of terrestrial animals by 2100, with extinctions and ecosystem collapses becoming commonplace.”

Low Energy House’s construction

The rear extension of Low Energy House, features SIP panels, and does not have a continuous concrete slab. Instead, it has strip foundations, extending the suspended timber floor into the new addition. This significantly reduced the amount of concrete used.

We took down the ceilings to insulate between the joists, eliminating thermal bridges. As far as airtightness is concerned, we used a thick coat of lime plaster on the masonry, taped up at junctions like windows. This provides our airtightness layer. An Intello Plus membrane was used for timber construction such as the ground floor, the rear extension, and the entire loft conversion roof.

During construction, we doubled up timber beams and avoided using steel within the thermal layer in the loft conversion, thus avoiding the typical cold bridge associated with steel. We also circumvented ceiling-mounted downlights to prevent small cold bridges in the insulation layer. For the south-facing Velux, we used triple glazing and integrated external solar shading to reduce solar gain.


Loft Conversion at Low Energy House, Muswell Hill

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Airtightness and sustainable construction

Airtightness testing is a crucial part of the process. We sealed up the front door then pressurised the house with a blower fan. While the test is taking place, we used smoke to detect problem areas. The first airtightness test resulted in 5.2 changes per hour, while the second test, after addressing initial issues, is expected to measure at 3.5ach.

“If the current trajectory of greenhouse gas emissions continues, global warming is projected to condemn over one-third of animal and plant species to extinction by 2050. This would result in a catastrophic loss of biodiversity and drastic alterations to ecosystems globally.”

Cost of building Low Energy House

In terms of cost, the total contract sum was about £250,000. There were a few client supplied items on top of that, but overall, the total spent on low-energy items was about £34,000. This was mostly £10,000 for the MVHR system and £20,000 on insulation and air tightness. The cost uplift for triple glazing over double was fairly small, about £4,000.

As for low embodied energy items, using timber instead of steel and stone instead of concrete had no extra cost, making it a no-brainer. A point to note is that the form factor, which is hard to influence in a retrofit, is generally relatively good for London terrace houses due to their compact form and shared heated walls with neighbouring buildings.

“Over the past 50 years, global biodiversity has alarmingly declined, with wildlife populations plummeting by an average of 69%.”

We hope that these sustainable house refurbishment ideas provide inspiration for your project. The benefits are numerous, including comfort, health and energy efficiency. Even without a deep refurbishment, simple measures like draft proofing, secondary glazing, and eliminating thermal bridges can make a significant difference. Its worth noting that if you’re able to reach Passivhaus standard, you will need very little in the way of any heating sources. Energy demand can therefore be met easily with on site renewables: making net-zero a real possiblity.

For more information about working with Architecture for London, please contact us on 020 3637 4236 to discuss your requirements, or visit our architecture project portfolio to see a selection of our previous projects.