The European Commission launched Horizon Europe in 2021 as its most ambitious research and innovation program to date, committing over 95 billion euros to accelerate scientific discovery and address the defining challenges in European cities. Among the initiatives that Horizon Europe funds is ReGreeneration, a transnational consortium uniting nine cities, their governing bodies, leading research institutions, and technology partners in the region.
Elevation is often framed as progress, lifting movement above the friction of the city and smoothing circulation into uninterrupted flow. Every act of lifting produces a secondary condition in its wake. Beneath flyovers, metro lines, and railway viaducts, a second ground emerges as shaded, ambiguous, and rarely planned with the same intent as what moves above. These spaces are not incidental leftovers. They are the spatial consequence of a design decision that privileges speed, clearance, and efficiency, redistributing value and visibility across the city in the process.
What lies below is not empty. It is structured, constrained, and defined by infrastructure, left without a clear role. Studies on elevated highways consistently describe these undercroft zones as residual spaces, formed when transport systems are conceived independently of the ground they pass through. An Arup report on spaces beneath viaducts notes how they often disrupt pedestrian continuity while remaining outside formal planning frameworks. Similarly, recent academic reviews of under-flyover environments highlight that these areas are rarely integrated into urban design strategies at all. The result is a peculiar condition: space that is physically present and structurally determined, but programmatically undefined.
Residential architecture continues to offer a productive ground for unbuilt exploration, revealing how architects respond to site, climate, and constraint at the scale of the domestic. In this Unbuilt edition, submitted by the ArchDaily community, the selected projects bring together a range of proposals that reconsider the house not as an isolated object, but as a spatial system shaped by its environment. These works position architecture as a framework that negotiates between ground, material, and inhabitation, often emerging directly from the conditions of the site.
Across varied geographies, from Kerala and Cartagena to Amman, Tromsø, and Zwolle, the projects demonstrate diverse responses to domestic architecture. They include compact urban dwellings organized through vertical layering, courtyard houses partially embedded within the ground, residences adapted to sloping terrains, and typological transformations shaped by regulatory constraints. Some projects explore linear spatial sequences rooted in traditional proportions, while others organize domestic life around atria or excavated voids that mediate light, ventilation, and privacy. Together, these proposals examine how the house can be structured through section, material, and environmental performance rather than formal expression.