How to retrofit a London home to the EnerPHit standard

London's housing is mostly old: Victorian terraces, Edwardian semis, solid brick and slate. They have a lot going for them, but most of them leak heat, cost a fortune to warm, and fall well short of the comfort we'd expect now. Older London homes are typically two to three times less thermally efficient than a house built to current regulations.

Knocking them down isn't the answer, though, both for the embodied carbon you'd waste and the character you'd lose. Retrofitting them well is, and EnerPHit is the standard that does it properly.

Low-energy extension to a Victorian home in London, designed to EnerPHit with triple glazing, natural materials and airtight detailing.

Why Now Matters

The homes we refurbish now will still be in use in 2050 and well beyond, which is the deadline the UK has set itself for net zero. Most of London's older housing was built when coal was cheap and the climate wasn't a consideration, and that inefficiency feeds straight into bills, comfort and carbon.

Retrofitting a Victorian house to a high standard doesn't just make it warmer, it takes a large, long-lived source of emissions and brings it close to a modern one. There's a great deal of that housing, so it adds up.

A whole-house approach

EnerPHit isn't a set of separate upgrades, it treats the house as one system. The useful comparison is a well-made flask: stable, comfortable and low-energy because every part works together and there's no weak link letting the heat out. Five things make that work.

• A super-insulated envelope. Insulation to the walls, roof and floors cuts heat loss sharply. On older buildings we often use natural materials like wood fibre, which perform well and stay breathable, which matters on solid walls.

• Airtight construction. Draughts are one of the biggest sources of heat loss, so an EnerPHit house is sealed against uncontrolled air and moisture movement while keeping the warmth in.

• High-performance glazing. Triple-glazed windows, carefully detailed and often in FSC-certified timber frames, give modern comfort while keeping the character of the building.

• Mechanical ventilation with heat recovery. MVHR removes stale air and brings in fresh, filtered air, recovering up to 90% of the heat that would otherwise be lost.

• Eliminating thermal bridges. Even a small gap in the insulation causes heat loss, cold spots and, over time, condensation and mould, so the detailing at every junction has to be right.

Done together, this gets an existing house to a space heating demand of around 25 kWh/m² a year, a fraction of what it started at.

Refurbishment without losing character

There's a fear that performance upgrades mean stripping out everything that makes an old house worth keeping. They don't. The sash windows, the brick arches, the lime plaster, these are things we work with, not against.

On a recent North London retrofit, we kept the solid brick structure and added a breathable insulation layer finished in natural lime plaster, so the wall still regulates moisture rather than trapping it, which protects the original fabric. The MVHR was concealed in floor voids and joinery to keep the interiors clean, and the windows were replaced with purpose-made triple-glazed units detailed to match the originals. The improvement is felt in how the house performs, not in what it lost.

It starts with measurement

Every EnerPHit retrofit begins with investigation rather than assumption. Before we draw anything, we thermally image the walls, assess where condensation could form, check air quality and survey the existing materials. Then we model how heat, moisture and air will behave once the upgrades are in, alongside the practical things: how the sun moves through the rooms, where heat is actually needed, where summer overheating is the risk.

The result is a retrofit designed for that specific house rather than pulled off a checklist, which on solid-walled buildings is the difference between a wall that performs and one that quietly grows damp.

A phased plan, if required

Budget and disruption don't always allow a full retrofit in one go, and that's fine. The EnerPHit Retrofit Plan lets you phase the work while still aiming at certification. If you can't replace the windows this year, you can start with airtightness and insulation and come back to glazing later.

The key is sequencing it so each stage supports the next rather than undoing earlier work, which is the trap an unplanned, piecemeal approach falls into.

Renewables, once the fabric is right

When the envelope is performing, the remaining energy demand is small, and that's the point at which renewables make sense. An air source heat pump draws heat from the outside air, even in winter, to run heating and hot water, and paired with solar panels and battery storage it can get a house close to net-zero in operation.

The order matters, though: heating systems work best when the building barely needs heating in the first place, so the fabric comes first and the kit second.

A late-Edwardian house in West London

On a current project, a late-Edwardian house in West London is being reworked with EnerPHit at the centre of it. The owners loved the proportions and detailing but were tired of cold winters, rising bills and a house that overheated in summer. The brief was to retrofit without losing the character.

We used breathable wall build-ups with wood fibre insulation, lined the roof with vapour-open membranes, upgraded every window to triple glazing, and ran a concealed MVHR system through the floor voids and eaves. The house now runs quietly and efficiently, and holds a steady, comfortable temperature through the year, while still reading as the building it always was.

Retrofitting London's older housing to EnerPHit is one of the most effective things we can do: it cuts emissions from buildings that would otherwise keep leaking energy for decades, keeps the character of the street, and produces homes that are genuinely comfortable and cheap to run.

It takes patience and precise detailing, but it's some of the most worthwhile work we do. If you're thinking about retrofitting your home, we'd be glad to talk it through.

→ Email us at architects@risedesignstudio.co.uk
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