The energy bill of almost every home in Britain will rise today — typically to £1,849 a year — but not that of Henrik Brodtkorb and Inbar Linenberg. That’s because their 100-year-old terrace in north London no longer has any energy bills. In fact, their supplier had to pay them £69 for their year’s electricity use.
The house has had what sustainability geeks call a “deep retrofit”, which turned it into a high-performance, low-energy home. To Brodtkorb and Linenberg, though, the term “retrofit” is still unfamiliar when I mention it.
Their aim was to make a mid-terraced house comfortable and healthy. The couple wanted space to bring up their toddler, Asker; to host his family from Norway and hers from Israel. They wanted to build “something that will last, that doesn’t need redoing every five or ten years”, says Linenberg, 31. “Then Siri [Zanelli of Collective Works, their architect] was, like, ‘You guys could do something really powerful here.’” And so, a renovation became a retrofit.
When they bought the unassuming house for £790,000 in 2021 it looked just like countless others up and down suburban streets all over Britain. The floorplan felt small and narrow. Yet Linenberg, a nutrition researcher, fell in love with its location near Hampstead Heath and with “all these wonderful Mediterranean things in the garden. It had olive trees, it had a fig tree, it had grapevines. We saw the potential in it.”
In an eight-month project, Oasis Construction gutted the 1,075 sq ft house top to bottom and added 540 sq ft of extensions — a main bedroom suite in the bold rust metal-clad loft and a near-10ft kitchen extension with a striking saw-tooth roof. The vaulted kitchen ceiling is beautifully panelled in oak, above the terrazzo island where Linenberg can hold her Slikkepott chocolatier classes.
On a chilly morning, sun streams in through the kitchen roof lights as we gather in the cosy dining nook. Brodtkorb, 32, a data engineer, shows me their energy use on his phone: “We’ve produced more than we’ve used.”
In the first 11 months of 2024, 11 solar panels on their roof generated 3.2 megawatt-hours (MWh) of electricity, while they consumed 2.6MWh. They don’t have a battery (yet) so self-consumed 0.9MWh of the 3.2MWh they produced, while exporting 2.3MWh to the grid and importing 1.7MWh.
Yes, they have an air source heat pump. It stands in the neat front garden, turning the electricity it uses into 3.5 times as much heat — powering the underfloor heating system and hot water. That’s far more efficient than a typical gas boiler, which turns the fuel it burns into 0.9 times as much heat.
But the real magic is in the fabric all around us. Windows are triple-glazed. Those in the roof have five layers, with film interspersing the three layers of glass. “It makes a difference on the noise levels as well,” Linenberg says.
They added external wall insulation everywhere, covered in terracotta render that nods to Linenberg’s Mediterranean heritage. Thermafleece wool insulation went into the loft; the kitchen extension is built with Steico timber-frame panels filled with wood fibre insulation.
Adding insulation to an old building “obviously helps”, Zanelli says, but it is actually the improved airtightness that “makes a huge difference”. It is like “wearing a big woollen jumper”, she explains. “It keeps me warm. But if the wind blows, the wind goes straight through my jumper. So I put my windbreaker on top for the hot air to stay inside to keep me warm. If not, it just goes out.”
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Zanelli, who is Norwegian, says: “I freeze more in England than in Norway. In this country, a lot of people have not ever experienced a comfortable house. People buy this sausage cushion and squash it up against their front door and think that’s normal. It’s mad. In Norway, sausage cushions do not exist. There, it’s normal to be comfortable inside. Draughty doesn’t have to be normal.”
With meticulous attention to detail, the builders lined the house with an airtight membrane and taped every junction, corner and nail puncture with airtightness tape. “It’s not a highly skilled or complicated task, but someone needs to be very diligent and know exactly what they’re supposed to do. I think that’s why a lot of people haven’t done it,” Zanelli says.
The house leaked only 1.8 cubic metres of air per hour per square metre when pressure tested at 50 Pascals — compared to 13m³/h. m² for a typical Victorian terrace and 8m³/h. m² for a new-build.
Next they had to add controlled ventilation. Without it, you end up with damp and mould. “In Norwegian homes, no matter how old, we immediately notice the different air quality. Things dry properly. There’s no damp feeling like when you’re in lots of British houses,” Linenberg says.
The couple fitted a mechanical ventilation with heat recovery (MVHR) system. It extracts warm, stale air from the kitchen and bathrooms, then uses the heat from it to warm fresh air pumped in from outside.
It works so well that they don’t have towel radiators or a tumble dryer. “It’s funny because my parents [who live in Britain] have been, like, ‘You need towel radiators.’ We don’t. Everything dries perfectly fine.”
There is beauty too. The bathrooms (brief: Mediterranean spa) feel like jewel boxes with Moroccan-style zellige tiles from Mandarin Stone. Brodtkorb’s home office is drenched — ceiling included — in teal blue Burlington Arcade from Mylands.
Slowly, the family is furnishing their home with finds from Facebook Marketplace and Gumtree. “They’re not fancy people, but their house envelope is extremely high quality,” Zanelli says. “They wanted to do this right.”
A deep retrofit does not come cheap. Brodtkorb won’t say what they spent on their renovation, but estimates that the eco elements added 20 per cent to the cost.
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According to Collective Works, the base cost of a standard home renovation in London is £2,500 per sq m, excluding second fix items (such as kitchens, bathrooms and carpentry). Labour costs tend to be lower elsewhere in the country. Upgrading such a renovation to a deep retrofit costs an extra £450 per sq m for fabric upgrades, plus £5,000 for solar panels, £7,000 for an air source heat pump (after deducting the government’s heat pump grant) and £8,000 for an MVHR.
Perhaps unsurprisingly, only 800 to 1,000 UK homes a year undergo a deep retrofit, the National Retrofit Hub, an advisory service, reported last year.
Brodtkorb and Linenberg will save the full cost of their fuel bill — that’s £1,849 a year from today — and got £2,000 cashback off their mortgage. However, the couple do not measure the return on their investment in simple monetary terms.
“It’s the comfort thing,” Brodtkorb says. “We knew that we were going to live here for a long time. At that point you can start thinking about investing in your own future rather than just investing for your finances. If we sold it today, maybe we would break even. But the mathematics change depending on the time horizon.”
A £15,000 route to zero bills
Soon you may not need to insulate your home top to bottom to eliminate energy bills. Green technology has turned a Victorian terrace in Walthamstow, east London, into the first existing UK home to qualify for the Zero Bills tariff from Octopus Energy — so the residents will pay no energy bills for at least five years.
Crucially, the terrace did not have to be gutted for fabric upgrades. It already had double glazing and loft insulation, but was by no means a low-energy home. To transform it into a zero-bills home, it only needed solar panels, a battery and a heat pump. Total cost? About £15,000 and two weeks’ work.
“It was surprisingly easy,” says Chris Brown, a director of Future Fit Homes, which owns the terrace as a buy-to-let. The tenants received their first £0 energy bill last month — down from £134 a month (£1,608 a year) in the year to February 2024.
The house is among a series of trials by Octopus, Britain’s biggest energy supplier, with an aim to roll it out to homeowners and landlords everywhere. “We think there’s at least 500,000 homes that could be suitable for a zero bills retrofit upgrade,” says Nigel Banks, the company’s technical director. “It’s not going to be possible for every house to get to a zero energy bill, but the same technologies can enable people to massively reduce their bills.”
Banks adds: “The cost of solar panels and batteries have come down. Smart tariffs can maximise the financial benefits of those and of smart-controlled heat pumps. You can now deliver much bigger energy savings and financial savings through technology than you can with disruptive deeper insulation measures.”
To qualify for zero bills, you need a roof big enough to fit sufficient solar panels — but not so big that the house’s energy use is high. Homes also need to be “reasonably well insulated”, Banks says.
Despite being mid-terrace, the Walthamstow pilot house could fit just enough solar panels — 6.1 kilowatt-peak (kWp) — to balance out its energy use: 12 Aiko photovoltaic panels of 510W each, on both the north and south-facing sides of the pitched roof.
Conventional wisdom is that solar panels should face south for the best efficiency. Yet Brown says: “The extra cost of the panels on the north was definitely worthwhile and we wouldn’t have got the zero bills without it.” Most of the installation cost is for scaffolding and labour, while the panels themselves have become significantly cheaper and more powerful, he explains.
The solar energy is stored in an AIO GivEnergy 13.5kWh battery, so the residents can use their own electricity at night.
An air source heat pump (Vaillant aroTHERM plus 5kW) provides heating and hot water without burning fossil fuels. Five radiators had to be swapped for bigger ones, but it was “straightforward”, says Tanya Fairtlough of Future Fit Homes, who managed the project. A good engineer is key to correctly design and install the heat pump system. That will determine its efficiency, which can vary as widely as 250 per cent to 450 per cent.
“Don’t be so daunted about the heat pumps,” Fairtlough says. “A lot of articles ramp up bad news stories about heat pumps. But this house is really warm — it’s warmer than mine, which has a gas boiler — and they’ve got zero bills.”
