Reiken II (tweezicht)

Retrofit: Improving the energy performance of existing buildings and structures by upgrading them with contemporary systems and technologies

A historic townhouse on Papegaaistraat in Ghent. The challenge of radically improving sustainability here is twofold.

First, this is a heritage building in which many decorative elements have been preserved. The house lies in the heart of Ghent, within the buffer zone of a listed urban view (Coupure), under the strict eye of heritage authorities. The front façade is largely intact and highly valuable, and many of the reception rooms still feature mouldings, historic fireplaces, and original floors.

Second, the plot is exceptionally small, only 78m². About 43m² is occupied by the original townhouse. Including the historic rear wing brings it to 48m², but over time, more was added until the site was completely built over. Such a limited footprint adds further complexity, especially for sustainability measures that come with requirements for placement, acoustics, or scale.

Sustainability is the sum of many interwoven elements. It goes far beyond insulation, heat generation and ventilation, encompassing also overheating prevention, rainwater management, the cooling effects of gardens, and in a broader sense, circularity and biodiversity.

Insulation, at its core, begins with minimising the surface area of thermal loss, building as compactly as possible. The plot may be small, but the house is quite large. That allows us to reorganise all functions within the main volume and eliminate the rear extensions to create an urban garden. One immediate benefit is that the building becomes highly compact. It tucks itself neatly between the party walls from front to back, greatly reducing exposed surfaces.

The rear façade is insulated using a colourful, 22cm-thick STO system. But this insulation does more than just insulate: smaller windows are pushed deep into the façade, so they automatically shade themselves in summer. Larger windows are brought forward and fitted with blinds. The façade is topped with a curved plaster cornice. Aesthetically refined, but also designed to ease the transition to roof insulation.

The roof insulation is a special case. The original timber structure is beautifully intact on the inside. And the headroom near the top landing is limited. These two factors led to the choice for a sarking roof. Insulating over the rafters instead of between them. This way, the entire timber structure, including the boarding, remains visible from within, and the interior height stays unchanged. But not just any sarking roof: most use rigid materials like PUR, which perform poorly against heat and are acoustically inferior. In this noisy street, PUR would amplify tram noise. Instead, we opted for rigid wood wool boards, dowelled into place, with an extra-wide batten at the solar panels to prevent wind uplift.

The high-performance insulation and the newly compacted volume made it possible to install a heat pump without needing to oversize it. This led to the next question: where do you place the external unit? A tiny city garden in a dense block is not ideal. So an internal terrace was carved out of the roof volume. It offers a stunning view over the Coupure and Ghent’s old city centre and also discreetly houses the outdoor unit, free of disturbance. The heat pump feeds fan coil units in all rooms. Underfloor, wall, or ceiling heating wasn’t an option due to the historical finishes. In some cases, creativity was needed to integrate the fan coils as compactly as possible, hidden inside kitchen cabinets, for example.

Managing cold is one thing; heat, another. The heat pump (and thus the fan coils) provides both heating and cooling. Active cooling is a comfort, but it does use energy. The design prioritises keeping heat out in the first place, and makes smart use of night cooling. The staircase acts as a chimney for fresh night air, by opening a window below and the rooflight above. Simple, but it works. City heat lingers longer than in rural areas, but even compact gardens have now proven cooling effects. In this project, the garden, made possible by the building’s new compact form, plays a key role in regulating the home’s climate. Only when passive measures no longer suffice is the active cooling brought into play.

A heat pump is sustainable, but it still uses electricity. Even though roof area was scarce, and rooflights were required on the south side for views, we still managed to install 10 solar panels. The south-facing roof became a compact puzzle of rooflights, solar panels, and service penetrations. A home battery was also installed, decoupling production from consumption.

Water is another crucial theme. Climate change pushes towards extremes: too much or too little. On a plot this tight, water management poses challenges. The story begins with unpaving. At the start, the site was 100% hard surface; no rainwater was absorbed or reused. By moving all living functions into the main volume, demolishing the rear extensions, and creating a garden, we have now unpaved 35% of the site. Rainwater from the main roof is directed either to a restored underground cistern in the garden, or to a surface tank on the roof terrace. Unexpectedly, a five-metre-deep groundwater well was discovered in the garden. In the spirit of frugality, this is connected only to an outdoor tap: used for irrigation, any excess water simply returns to the aquifer. To prepare for the future, the plumbing of the entire house has been laid out to allow for future greywater reuse. A system can later be plugged in to filter lightly contaminated water for local reuse.

Circularity was also (to a limited extent) a part of the project. Wherever possible, dry joints were used instead of wet ones, allowing for future disassembly. Many elements were reused. Sometimes elsewhere in the house, sometimes after restoration.

Finally, the garden brings a real boost in biodiversity. It has been planted with a wide range of native species. A small pond in dappled shade (without fish, and thus no need for filter or pump) attracts dragonflies and, potentially, frogs. There are feeding stations and nesting boxes. A bee hotel and a shelter for butterflies.