In one coastal city, a retrofit shows a different path to comfort.
Residents there now sit in shirtsleeves, with indoor thermometers reading 23 °C even as radiators stay silent. The route to that outcome says a lot about design, finance and everyday life.
Brest shows a new normal for winter comfort
In Brest, western Brittany, one apartment block has become a talking point. The building runs warm through the darkest months, yet residents barely touch the heating. This is not a trick. It is the result of a full-scale renovation that focuses on the building envelope and the way sunlight interacts with it.
Engineers tightened the shell, reduced leaks and harnessed solar gains. The restoration sealed gaps, upgraded façades and rethought balconies. The outcome feels dramatic indoors: temperatures stay steady and drafts fade. Rooms warm up when the winter sun breaks through, and the new skin keeps that heat inside.
Heat losses were cut by more than 70%, the energy rating moved from D to B, and indoor readings reached 23 °C with the radiators off.
What changed in the building envelope
The project hinged on the fabric. The teams worked outside-in, turning a leaky block into a tight, solar-aware shell. Here are the key moves that shaped the result:
- Insulated façades to create continuous thermal protection and reduce cold bridges.
- A renewed roof to limit upward heat escape and improve weatherproofing.
- Conversion of open balconies into glazed buffers using high‑performance curtain walls.
- Reconfigured openings to manage sunlight while cutting infiltration.
- Careful detailing around junctions to maintain the uninterrupted thermal line.
These steps form a coherent strategy. They trap paid-for heat, catch free heat from the sun and smooth out daily swings. The result is less reliance on combustion and more comfort for the same winter light.
The balcony effect that changes the daily feel
Closed balconies made the difference. Once exposed to the wind, they now act as sunlit airlocks. On a bright day, the glass warms the space through a modest greenhouse effect. That warmth sits between outside and inside, raising the temperature of the rooms that open onto it. With decent glazing and an insulated slab, the buffer loses its heat far more slowly after dusk.
Enclosed balconies behave like low‑tech conservatories: they harvest daylight, calm the wind and feed gentle gains into living spaces.
This is not just about hotter rooms. It also stabilises the microclimate within the flat. Fewer chills at ankle height. Fewer cold panes. Less moisture condensing on corners. The experience improves because the envelope and the sun now cooperate rather than fight.
Before and after at a glance
| Indicator | Before works | After works |
|---|---|---|
| Energy rating | D | B |
| Thermal losses | Baseline | More than 70% lower |
| Typical winter indoor temperature (sunny midday) | Variable, often below comfort | Up to about 23 °C reported |
| Heating run‑time on sunny winter days | Frequent | Often not needed |
Money, grants and the quiet machinery behind success
The price tag reached €1.58 million for the block. Public support covered around 45% of that, with money coming from the Brittany Region, Brest Métropole and the national housing agency Anah. A local public service, Tinergie, coordinated technical studies and funding routes so the co‑owners could move together.
The region has set a strong pace for the years ahead, with an ambition to upgrade about 45,000 homes annually. The logic is clear: improve the stock at scale, curb energy demand and blunt price shocks for households. This Brest case shows the pattern: bundle measures, line up grants, and secure a result that residents can feel every time they step inside.
Could you copy it in your own block?
Yes, if the conditions fit. The core lesson is to stop heat from leaking and to value winter sun. That means fabric first, then controlled solar gains. Blocks with existing balconies or recessed loggias have a head start, because those spaces can become thermal buffers with the right glazing and seals.
- Check orientation. South and west façades capture the most winter sun.
- Assess the structure. Balconies, fixings and rails need proper engineering before glazing.
- Plan for shading. Summer sun can bite; add blinds or external shading to avoid overheating.
- Improve airtightness in tandem with safe ventilation to manage moisture and indoor air quality.
- Coordinate as a co‑ownership so works align, warranties hold and grants land.
Fabric first, then solar gains: seal the leaks, insulate the shell, and use quiet daylight as the cheapest heater you own.
A simple savings sketch
Consider a typical flat that used 12,000 kWh a year for space heating. A 70% cut would save 8,400 kWh. At €0.23 per kWh, that equals about €1,932 a year. At €0.30, savings reach €2,520. These are ballpark figures, not promises, and real outcomes vary with orientation, weather and occupant behaviour.
What to watch out for
- Moisture control: better sealing must go with planned ventilation to avoid condensation and mould.
- Summer comfort: add shading and consider solar control glass where exposure is strong.
- Fire safety: curtain walls and insulation systems need compliant details and tested products.
- Glare and acoustics: large panes alter light and sound; specify coatings and seals to suit.
- Permissions and heritage: glazed balconies may need approvals, especially on street façades.
Why this matters beyond one French postcode
Gas price spikes have left many households wary of the next bill. Buildings that keep warmth inside cut that anxiety. A warmer, steadier home also supports health. Fewer cold spots mean fewer damp corners, which helps lungs and reduces repairs. Blocks that decarbonise heat demand then face easier choices on the next step, whether that is lower‑temperature systems or shared heat pumps.
The Brest model is not exotic. It uses known tools—insulation, airtightness, decent glazing, careful detailing—and applies them as a package. The twist lies in turning balconies into useful thermal space, rather than treating them as a permanent heat sink. That shift unlocks a quiet supply of free warmth on short winter days.
Terms to know
- Building envelope: the insulated shell—walls, roof, floor, windows—that separates inside from out.
- Curtain wall: a non‑load‑bearing glazed façade that hangs from the structure and seals the weather.
- Thermal bridge: a junction where heat sneaks through, often at slab edges or window surrounds.
Try a quick home simulation
Keep a small data logger on your balcony and another in the living room for two winter weeks. On sunny days, track the balcony temperature rise and the lag before the living room warms. If the balcony already delivers a clear boost, glazing it may pay off. Share the graphs with neighbours to build a case for a joint project.
A pathway that stacks benefits
Groups that organise at block level can buy in bulk, hire one project manager and secure better grant terms. Add to that lower noise from the street, a cleaner façade and improved resale value. Households then gain comfort now and protection against future price swings, while the grid gains capacity as peak loads ease on cold evenings.
