Do You Need a Permit to Build an ADU (Accessory Dwelling Unit)? in Spanje
Usually yes. Building an ADU — whether a detached backyard cottage, a garage conversion, or an internal addition — nearly always requires a building permit because it creates habitable living space with its own plumbing, electrical, and egress requirements. Most jurisdictions require full plan review, structural engineering, and multiple inspections covering foundation, framing, plumbing, electrical, insulation, and final occupancy.
Do you need a permit?
Usually yes
- Permitting authority
- Ayuntamiento (Urbanismo) / Comunidad Autónoma
- Typical fee
- €500–€5,000
What triggers a permit
- Any new habitable living space (bedroom, kitchen, bathroom) regardless of square footage
- New plumbing connections or separate utility meters for the ADU
- Structural work: new foundation, framing walls, roof structure
- Electrical service panel addition or sub-panel for the separate unit
- Creating separate ingress/egress (entrance, exit windows, parking)
Country-specific detail
In Spain, building an additional dwelling unit — whether as an ampliación (addition) to an existing vivienda, a conversión of a local (commercial space) or garaje into housing, or new construcción of a vivienda auxiliar — requires a licencia de obra mayor from the Ayuntamiento. The project must comply with the CTE (Código Técnico de la Edificación) requirements for habitabilidad (habitability), including minimum superficie útil (usable area, typically 25–40 m² depending on the CCAA), ventilación (ventilation), iluminación natural (natural light), and aislamiento térmico y acústico (thermal and acoustic insulation). A cédula de habitabilidad (habitability certificate) must be obtained upon completion. The proyecto básico and proyecto de ejecución must be signed by an arquitecto colegiado, and the obra must be supervised by an arquitecto técnico (aparejador) as director de ejecución. In comunidades autónomas like Cataluña, specific regulations on viviendas de uso turístico may further restrict ADU usage.