Bioclimatic architecture in practice

Many people associate bioclimatic architecture with experimental houses. At STARC, it is above all a working method: we make use of the site, the sun, the mass of the materials and rainwater before adding any equipment. Here is how we apply this to three types of projects we regularly carry out in Wallonia and Brussels, with technical studies by Optibim.

A regulatory framework pointing in this direction

Bioclimatic design is no longer just a matter of comfort. In Wallonia, since 1 January 2021, new buildings must meet the NZEB or Q-ZEN standard (Q-ZEN being the Walloon equivalent of nearly zero energy). The SPW Énergie (Walloon energy administration) has added a further step: from 1 January 2026, all new and equivalent buildings will need to source at least 35% renewable energy in their annual primary energy consumption. For renovation, the requirements applicable since 1 January 2017 remain unchanged.

The practical Q-ZEN guide published by the Walloon Region actually describes purely bioclimatic principles. It states that buffer spaces (hallway, utility room, toilet, bathroom...) should be placed to the north, that openings to the north should be limited, and that, where necessary, the building should feature external solar shading: shutters, blinds, architectural overhangs, and so on.

The less energy you consume, the easier it is to reach the required renewable share. Good passive design therefore directly reduces the size of the technical equipment needed.

Case 1, a new build Q-ZEN house in Namur province

The starting point is a classic one: a gently sloping plot, a street to the north and the garden to the south. We organised the layout as follows.

• Living room and kitchen to the south and west, entrance, utility room and bathroom on the street side.
• Large openings to the south, smaller ones to the east for morning light, very little glazing to the north.
• Heavy floors and internal walls. The Walloon guide is clear on this: heavy internal partitions (concrete, brick...) store heat, which is then released during the cooler hours.

The roof overhang is sized using simple solar geometry calculations. At our latitude, the midday sun rises to around 63° at the summer solstice, and just 16° in winter. A one metre overhang therefore shades a south facing window around two metres high at midday in high summer, while still letting in the low winter sun. To the west, an overhang is not enough, as the late afternoon sun is very low. We provide external blinds there instead.

Optibim then checks in the EPB software (energy performance software) what these choices mean for overheating risk. We do not present this calculation to the client as a mere formality. It is used to fine tune the glazed area, the type of shading and intensive night time ventilation. A blower door test at the end of the works confirms that the building envelope is as airtight as planned.

Case 2, a courtyard farmhouse converted into housing

With older buildings, you do not choose the orientation, you inherit it. Fortunately, Brabant and Condroz farmhouses are often excellent, if unintentional, examples of bioclimatic design: thick stone or brick walls, few openings facing the prevailing wind, a sheltered courtyard.

Our approach to this type of project:

• A full survey by BimBot (3D scanner, drone, 360° photos) to model precisely the wall thicknesses, floor levels and the shading cast by the farmhouse wings.
• Insulation tailored to each wall, with careful attention to vapour migration within the old masonry.
• Living spaces placed in the wings facing the sunny courtyard, with the unheated barns used as buffer spaces.
• New openings cut only where sunlight and views justify them, respecting the rhythm of the existing facades, something closely examined by planning authorities under the CoDT (Walloon planning code).

The mass of the old walls, positioned inside the insulated volume, dampens heatwaves very effectively. It is an asset that poorly considered insulation can easily destroy.

Case 3, a Brussels building converted into flats

In Brussels, the constraints are different: narrow plots, party walls, shading from neighbouring buildings. The energy framework also pushes towards restraint. Bruxelles Environnement (Brussels Environment) states that from 1 January 2025, the date on which the planning permission application is lodged, it will be prohibited to install natural gas or oil boilers in new or equivalent projects, and that for collective housing this only applies where all the dwellings in the project are classed as new or equivalent to new.

For existing housing, the trajectory is already set: by 2033, every dwelling will need to reach at least EPB target 275 (EPB being the Brussels and Walloon equivalent of EPC), which corresponds to energy class E.

In an office conversion, the bioclimatic levers are concrete:

• Dual aspect flats wherever the structural grid allows, so they can be cooled at night by opening the windows.
• Replacing fully glazed facades with a more reasonable proportion of glazing, with external shading on the south and west sides.
• Keeping the exposed concrete slabs at ceiling level, which provide thermal mass.
• A green roof, which helps manage water and limits overheating on the top floor.

With lower heating and cooling needs, it becomes realistic to heat the building with a heat pump.

Rainwater is part of the project

A bioclimatic project also manages water where it falls. In Wallonia, the General Sanitation Regulation (Règlement général d'assainissement) sets out an order of priority. According to AIDE, the intermunicipal water treatment association, since 1 January 2017 article R.277 provides for discharge into surface water where infiltration is technically impossible or the plot lacks sufficient space, and only then into the sewer. In practice, the planning application file must demonstrate whether infiltration on site is possible, notably through infiltration tests and a rainwater management study.

As for rainwater tanks, the Walloon government has confirmed to the Walloon Parliament that there is currently no general, systematic requirement to install one in new buildings, unlike in Flanders and the Brussels Capital Region. Even so, we almost always recommend one, connected to the toilets and garden watering.

Optibim carries out the hydrological studies, sizes the swales and infiltration zones, and handles CertIBEau certification for new connections. A well placed swale also helps cool the garden in summer.

What we take away from these projects

• Bioclimatic decisions are made at sketch stage. Moving a window or a living room after permission has been granted is costly.
• Overheating has become the real issue, more so than heating. It needs to be addressed at design stage, not fixed later with air conditioning.
• Thermal mass needs to sit inside the insulation layer, and remain exposed.
• In renovation, an accurate survey avoids unpleasant surprises and allows shading to be modelled correctly.
• Water, energy and summer comfort are all part of the same thinking. It is far simpler when the architect and the engineering firm work together from the outset.

Do you have a construction, renovation or conversion project in Wallonia or Brussels? The architects at STARC and the engineers at Optibim can look at orientation, summer comfort, EPB requirements and rainwater management with you, right from the first sketches. Get in touch with us in Gembloux for an initial meeting.