Housing for millions without new buildings? An analysis of the theoretical housing potential of under-occupied dwellings in the European building stock

Overview of Study and Authors

The article “Housing for millions without new buildings?” is an open‑access letter published in Environmental Research Letters by Jonas Lage, Luisa Cordroch, Johannes Thema, Florin Vondung, and David Schöpf. The authors are affiliated with Europa‑Universität Flensburg, TU‑Dortmund, and the Wuppertal Institute, reflecting expertise in housing policy, environmental research, and sustainability. Their work is funded by the German Federal Ministry of Education and Research (BMBF) under the FONA programme.

Core Research Question

The paper investigates the theoretical housing potential that could be unlocked by better using under‑occupied dwellings across the European Union. It asks how many additional three‑room flats could be created without new construction, using occupancy regulations from Swiss cooperatives as a benchmark (minimum occupants = rooms – 1).

Key Quantitative Findings

• Approximately 152 million rooms in the EU housing stock meet the “rooms – 1” under‑occupancy criterion; of these, 65 million meet the stricter “rooms – 2” criterion.
• This translates to a theoretical capacity for 50 million three‑room flats, enough to house 100 million people – about 23 % of the EU population.
• Under‑occupied rooms are concentrated in larger dwellings: 59 % of four‑room flats, 72 % of five‑room flats, and 86 % of six‑plus‑room flats are under‑occupied.
• Owner‑occupied homes contain 79 % of under‑occupied rooms and 76 % of under‑occupying households, indicating a strong link to private housing stock.
• Geographically, 41 % of under‑occupied dwellings are in cities, with the remainder split between towns (≈30 %) and rural areas (≈30 %).

Demographic and Income Patterns

• One‑person households account for 49 % of under‑occupied rooms, two‑person households for 38 %.
• Households without children, especially older adults, show the highest under‑occupancy rates.
• In most EU countries, higher equivalised income correlates with greater under‑occupancy, though several Central and Eastern European states (e.g., Bulgaria, Croatia, Estonia) display the opposite trend.

Methodology Overview

The authors used micro‑data from the EU‑SILC survey, applying the Swiss “rooms – 1” and “rooms – 2” thresholds to identify under‑occupied dwellings. Weights from the survey allowed scaling to the full EU population. Room counts exclude bathrooms, kitchens, and corridors; a six‑room category aggregates all dwellings with six or more rooms.

Comparative Context with Switzerland

Swiss cooperative and municipal housing applies the same occupancy rule to about 70 % of its dwellings, achieving higher occupancy efficiency. The paper argues that adopting similar institutional frameworks could unlock a comparable share of the EU’s theoretical potential.

Barriers to Realising Potential

The study outlines four main constraints:

1. Demographic – shrinking populations in some regions limit demand for new occupants.
2. Technical – existing layouts may not suit shared living or subdivision.
3. Economic – tax, legal, and market conditions can make co‑housing financially unattractive.
4. Cultural – social norms often view large flats as status symbols, reducing willingness to downsize or share.

Policy Implications

• Promoting affordable, attractive housing options for older adults and small households could free larger flats for families.
• Institutional reforms that embed occupancy requirements in non‑profit and public housing can increase the share of usable space.
• Coordinated policies addressing technical retrofitting, fiscal incentives, and cultural acceptance are needed to convert theoretical capacity into actual housing units.

Scale Relative to New Construction

The estimated 100 million‑person capacity equals 31 times the annual new‑construction output of the 23 EU countries with available data for 2022, highlighting the magnitude of untapped existing stock.

Outlook and Future Research

The authors call for country‑specific studies to refine potential estimates, assess feasibility, and design tailored policy instruments. Further work should also examine the environmental benefits of reallocating existing space versus building new units, to support the EU’s climate and resource‑efficiency goals.