Old bones, new life: retrofitting a Bathurst Mews house to EnerPHit

Behind the grand stuccoed avenues of Bayswater sits one of London's quieter corners: Bathurst Mews. A cobbled street once home to horses and hay carts, it is now a pocket of heritage houses where ivy climbs the brick and life goes on behind pastel-painted doors.

Behind the picture-postcard front, though, these old houses tell another story, one of energy loss, discomfort and environmental cost. This is how we are changing that story for one of them.

The street, and the problem

Bathurst Mews is part of London's fabric in the truest sense. Mews houses were built for stable hands and carriages, humble, utilitarian and mostly overlooked, and have since become some of the most sought-after homes in the city. But beneath the charm is a problem common to much of London's historic stock: they leak energy. No insulation, single glazing, cold bridges at every corner, and air that escapes as fast as the heat it carries. In winter you wear a jumper indoors; in summer the house stifles. For the people living in them, that is more than uncomfortable. Over a building's life it is unsustainable.

The EnerPHit answer

Our response was not to tear down and rebuild, but to keep the building and make it perform, with some respect for how it was originally built. EnerPHit is the retrofit version of the Passivhaus standard: where Passivhaus sets the benchmark for new low-energy buildings, EnerPHit sets it for existing ones, and it is not for the faint-hearted.

Meeting it here means wrapping the building envelope in super insulation, fitting triple-glazed timber windows throughout, sealing every junction to form a continuous airtight layer, and installing mechanical ventilation with heat recovery (MVHR) so the house gets fresh, filtered air with almost no heat loss. Solar panels go on the roof, the materials are chosen for low embodied carbon, and the insulation is natural and breathable where the old structure needs it, lime plasters and limewash finishes over the build-ups, limestone floors at ground and basement, and reclaimed timber used where cladding is called for, so the historic fabric can go on managing moisture the way it always has.

This is not a facelift. It is a full systems upgrade, and the modelling points to an 80 to 85% reduction in energy use, with year-round comfort and consistently good indoor air, all without losing what makes the house worth keeping.

Heritage and performance, both

The reasonable question is how you do all that without damaging the character of a heritage street. The answer is knowing what to hold onto and what to change. Preservation doesn't mean stasis.

The front of the house keeps its original brickwork, its sash-style windows (now triple-glazed) and the human scale that makes the street what it is. Behind that face, the story is different: the insulation is concealed within carefully detailed build-ups, the services are run with precision, the ventilation outlets are discreet, and the solar panels are placed out of the street's sight. From the cobbles, nothing has been lost. From inside, everything has changed.

The carbon cost of doing nothing

The saying goes that the greenest building is the one that already exists, but that is only true if the existing building is made to perform. The built environment accounts for around a quarter of the UK's carbon emissions, and a large share of that is the heating of homes exactly like these. London's stock of historic houses is uniquely rich and uniquely leaky, and left alone it will become steadily harder to live in as energy costs and summer temperatures climb. Retrofitting is not a cosmetic upgrade. It is how these buildings stay habitable, affordable and worth inheriting.

Six lessons from Bathurst Mews

Most UK homes of this age share the same construction: timber joists, solid brick walls, lath and plaster. The lessons from this project apply to nearly all of them.

Start fabric first. Before solar panels or any kit, tackle insulation, airtightness and the windows. The fabric always gives the biggest return.

Treat the house as one system. Every element interacts. Seal one part and ignore another and you can create condensation or cold bridging where there was none.

Ventilation is non-negotiable. Once a building is airtight it needs deliberate ventilation, and MVHR delivers healthy air without throwing the heat away.

Use natural, breathable materials. In older buildings especially, breathable construction regulates moisture and protects the fabric from mould and decay.

Engage the planners early. Even an unlisted building may sit in a conservation area. Early conversations and clear, well-considered proposals smooth the path.

Choose a team that knows retrofit. This is not new build. It demands a forensic understanding of existing fabric, thermal bridging and sequencing, and an architect and contractor who have done it before.

Not just for grand designs

We have applied the same principles to mews houses, terraces, schools, restaurants and cultural buildings, and the principle holds at every scale: work with what exists and help it perform. You don't need a large budget to benefit. Even partial measures, better glazing, internal wall insulation done properly, make a real difference, and as more homes take this route the cumulative effect across a street, then a city, is substantial.

There is one more reason to retrofit, and it isn't measured in kilowatt-hours. These buildings carry stories, layers of lives lived in them, and a retrofit done with care keeps all of that while making the house calm, warm and healthy to live in. That is what we are doing at Bathurst Mews: not preserving a relic, but giving a good building another century of use.

If you own an older home and are wondering what a deep retrofit could do for it, we'd be glad to talk it through.

→ Email us at architects@risedesignstudio.co.uk
→ Or call the studio on 020 3947 5886

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