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With a shared passion for energy efficiency, Toni McDermott and her husband, Francis Miers, planned to retrofit their small Clerkenwell house to Passivhaus standards. However, when it proved technically impossible, they began the search for a home to fit the bill.

It wasn’t easy to find the sort of property they wanted that could be altered to meet their eco-requirements. In any conventional house it means adding extensive insulation, air- or ground-source heat pumps, specially glazed windows and an awful lot of concealed ducting to circulate air.

All that needs specialist architects who work to a very high spec.

Hidden secret: listed terrace house was taken back to its bones for an eco-fit (Alan Parker)

Because Passivhaus-type homes have to be almost airtight — though you can open windows — everything must fit to within a millimetre. It’s a particular challenge in older houses, which are often wonky to some degree.

A HOUSE WITH GOOD BONES

Toni, 41, who works in finance, asked their estate agent about one particular street in Bloomsbury lined with big Regency houses, many used as offices.

The agent found one that was rented by a pharmaceutical company, and the couple went to view. The five-storey, 4,900sq ft house was listed, and wasn’t in bad repair — but looked like a dentist’s waiting room inside.

An experiment in eco-living: Toni McDermott and Francis Miers in the chic modern kitchen-diner — with period features (David Butler)

Huge ventilators poked through the windows, the floors were covered in lino and there was no proper bathroom or kitchen.

However, many original features remained, including box shutters, cornices and fire surrounds. “We got a tingle,” says Francis, 49, who works in IT. With its tall sash windows and east-west light, they knew the house had good bones and was beautiful underneath. Since they would have to strip it back, it was now or never to go eco, too.

They put in an offer in winter 2012, but though they exchanged in spring 2013 they had to wait till summer for the company’s lease to expire. Before exchanging they checked with the council whether they could convert it back to a family home and had a survey done to make sure an energy-saving retrofit would work.

Blend it: light parquet flooring and subtle colours and furnishings let the spectacular light and grand proportions of the house speak for themselves (Alan Parker)

A WOBBLE OVER WINDOWS

Having bought, they rented a house a few streets away for them and their children Honor, now 11, Joe, eight, and Fred, four, and began the hunt for an architect. After trawling the internet and interviewing four specialists they chose Robert Prewett, who they really got on with. Since it would be an 18-month job, that good relationship was essential.

The planners liked most of their ideas, including adding insulation everywhere and putting in two air-source heat pumps — massive beasts that have their own rooms — from which ducts run through walls and between floors. Fortunately the house is so solidly built, there was ample space for that.

Super-smart space for the kids: an oak stair leads down to the basement playroom (Alan Parker)

However, there was an argument over the windows. Their architect wanted to put in bespoke secondary glazing, which meant moving the box shutters in a bit. But the conservation office wanted the single glazing kept — making it impossible to hit the couple’s energy target.

After discussion and models, and the support of the Green Party’s Sian Berry, the planners agreed and the architect sourced special Japanese glass to keep the profile super-narrow, which looks terrific and removes street noise.

DESIGNED FOR LIFE

Subtle design ideas abound in this home, from a playroom in the basement with its own oak stair, to a sleek, teak terrace that was once a grotty asphalt roof lantern, to a cocktail area on a turn of the stairs with a gorgeous black-and-white mosaic floor.

The walls throughout are in various shades of grey, from French to Charleston. Most of the joinery is bespoke and quite mid-century modern, including Thirties-inspired marquetry wardrobes in the master dressing room, done by their interior designer. In the kitchen-diner there’s parquet all the way, but next to the kitchen island it is ceramic — an ingenious and practical touch.

Nothing jars or is showy. The proportions of the house and its spectacular light speak for themselves, endorsed by good-quality fittings and subtle colours. The sense that this is a radical experiment in eco-living is completely absent.

Thirties-inspired: stunning marquetry wardrobes in the master dressing room (Alan Parker)

Francis says: “Before we started, people asked, ‘Don’t Passive Houses steam up and smell of cabbage?’” The house smells fresh. Toni says: “It was pure luck hiring Robert, who introduced us to a brilliant builder and designer. If anyone wants to take a house back to its bones, they’d be mad not to eco-fit it, too.”

GET THE LOOK

To read more about retrofitting a house to this standard, go to Passivhaus Trust and Passivhaus