A simple, compact volume costs less to build and to heat than a house full of recesses and projections. We explain how to think this through from the sketch stage onward without sacrificing light or comfort, with 2026 price benchmarks and current EPB (energy performance of buildings) requirements.
A house with multiple recesses and projections often costs far more than expected, even though its habitable floor area stays the same. The most effective lever for keeping a new build within budget is not found in the catalogue of finishes. It lies in the shape of the building, and it is decided right from the first sketch.
What the 2026 figures tell us
Price benchmarks published this year vary depending on the source, but they all point the same way. For 2026, construction costs per square metre in Belgium generally range between 1,800 € and 2,500 €, excluding VAT and land.
What is more telling is the difference according to typology. A price guide published in 2026 gives the following ranges:
- Terraced house, 2 façades (compact): 1,450 to 1,700 €/m².
- Semi-detached house, 3 façades: 1,600 to 1,900 €/m².
- Detached house, 4 façades (all four sides exposed): 1,750 to 2,150 €/m².
- Single storey house: 1,850 to 2,250 €/m².
The same source notes that, for an equal habitable floor area, the foundation and roof represent a larger share of square metres than in a house with an upper floor. It also puts forward an indicative figure: each corner, each façade set back adds roughly 1,200 € to the shell and structure. This figure remains indicative, but it illustrates the mechanism well. On a 150 m² house, moving from one typology to another can mean tens of thousands of euros, before even discussing the kitchen or the tiling.
Why a simple volume costs less
Compactness has a precise definition. According to the Union des Villes et Communes de Wallonie (Union of Towns and Municipalities of Wallonia), the compactness of a building is the ratio between its protected volume and its total surface area of heat loss. In other words, how many square metres of wall, roof and floor need to be built to enclose the same heated volume.
Take a simple example. Two 150 m² houses over two storeys, each with a 75 m² footprint:
- a rectangle measuring 7.5 m by 10 m has a perimeter of 35 m;
- an L shaped layout with two recesses can easily exceed 45 m of perimeter for the same footprint.
Those extra 10 linear metres, over two storeys, add around sixty square metres of façade. Every square metre of façade means masonry, insulation, a brick finish or cladding, flashings, sills and junctions. On top of that come the corners, the valleys and hips of the roof, additional downpipes and waterproofing details. These singular points take time on site, and that is where most defects occur.
An advantage that continues after the build
Compactness does not only reduce the construction bill. It also makes it easier to meet energy requirements. According to the Service public de Wallonie (Walloon public service), since 1 January 2021 all new buildings must be nearly zero energy buildings. The practical Q-ZEN guide published by the Region (2026 edition) sets out the thresholds for a dwelling: K level: ≤ K35, E w level: ≤ 45, E spec level: ≤ 85 kWh/m².year.
The K level is determined by the thermal insulation properties of the construction elements and the compactness of the building. A compact house therefore reaches K35 with reasonable insulation thicknesses. A heavily articulated house sometimes has to compensate with more insulation, better frames or more costly techniques.
The 2026 context makes this even more important. The same regional guide states that at least 35 % of the energy consumed must come from renewable sources in new builds. The less heat a house loses, the easier that renewable share is to achieve, with a smaller heat pump or a smaller photovoltaic installation.
Compact does not mean dark or dull
This is the most common fear among our clients: that a simple box would feel bleak. In practice, the quality of a compact house lies in the interior and in how the openings are designed. These are the levers we use most often:
- Limit the depth of the plan. A volume that is too deep forces you to light the centre of the house artificially. By keeping a moderate depth, natural light reaches every living space.
- Place large windows in the right spot. A generously glazed south or west façade, with more closed north façades, gains light and solar gain without multiplying surface areas.
- Work with the section rather than just the plan. A double height void, a mezzanine or a sloped roof visible from inside give a sense of scale without adding a single extra corner to the façade.
- Keep outbuildings outside the heated volume. A carport, a garden shed or a timber canopy can enliven the composition. Built lightly and outside the protected volume, they stay cheap and do not weigh on the EPB (energy performance of buildings) rating.
- Take care with materials. A well chosen local brick, bluestone surrounds, a slate roof or timber cladding are enough to give character to a simple volume.
Local rules also matter. In Wallonia, a municipal planning guide or the character of neighbouring buildings can steer the volumetry, the ridge orientation or the roof pitch. We check these constraints before we start drawing, so that the compact shape is also the one that makes obtaining planning permission easier.
For investors and developers
On a residential building, compactness matters even more. Aligned volumes and floor plans that stack from one storey to the next make structural stability easier and allow technical ducts to be grouped together. They also limit costly load transfers. Each dwelling additionally benefits from the heated party walls of its neighbours. Corner flats or those under the roof, more exposed, need particular attention. A simple volume helps reduce their number or make better use of them.
For a developer, it is also a matter of schedule: fewer singular details mean a clearer site, more reliable quantity surveys and fewer extras.
How we build this in from the sketch stage at STARC
Compactness cannot be fixed at the end of the design process. Once planning permission is obtained, the shape is set. Our approach therefore follows a few simple steps:
- compare two or three volumetries from the sketch stage onward, with their façade and roof surface areas;
- test these variants against an initial budget estimate;
- have the K level and Q-ZEN feasibility checked very early by the engineering office Optibim, which works from our premises;
- keep the recesses that genuinely add something (a sheltered entrance, a protected terrace) and remove those that are there purely for effect.
Every corner should have a reason to exist. It is often this sorting, more than the choice of finishes, that separates a project that stays within budget from one that runs away from it.
Are you planning a new house or a small residential building and want to know which volumetry suits your site and your budget? Contact STARC in Gembloux. We will review your project with you and show you, sketches in hand, how much a well thought out shape can save you.
Frédéric Odent