🏚️ Can I build a garden shed without authorisation?

With conditions

Quick answer

It depends on the size. For a garden shed, the rule follows Planning Code thresholds: under 5 m² of footprint or floor area = no formality; from 5 to 20 m² = a prior declaration of works at the town hall; over 20 m² = a building permit. In an urban zone covered by a PLU, the permit threshold rises to 40 m². Note: surfaces add up, the PLU can impose siting rules, and the development tax applies from 5 m².

📋 The rules

Under 5 m²: no authorisation
5 to 20 m²: prior declaration at the town hall
Over 20 m²: building permit (40 m² in a PLU urban zone)
Building surfaces add up
Development tax due above 5 m²

🔓 Exceptions

The local PLU can impose distance, height or appearance rules
In a protected area (monument, classified site), formalities even under 5 m²
PLU urban zone: permit threshold raised to 40 m² (total floor area ≤ 150 m²)

⚠️ Penalties & fines

Building without the required prior declaration or permit is a Planning Code offence: the town hall can demand regularisation, even demolition, and fines of hundreds to thousands of euros per m² can apply. Unpaid development tax (around €930/m² outside Île-de-France, €1,054/m² in IDF in 2026, times the local rates) is also recovered. Better to file the dossier before building.

📎 Official sources

Last verified: 2026-06-20

❓ Frequently asked

Do I need authorisation for a garden shed?

It depends on the size. Under 5 m²: nothing. From 5 to 20 m²: a prior declaration at the town hall. Over 20 m² (or 40 m² in a PLU urban zone): a building permit.

Do surfaces add up?

Yes. Two 4 m² sheds make 8 m² and fall into the prior-declaration regime. Over 20 m² combined, a building permit becomes mandatory. The Planning Code adds the surfaces together.

Is there a tax?

Yes, the development tax applies to sheds over 5 m². In 2026 the flat value is about €930/m² outside Île-de-France and €1,054/m² in IDF, times the municipal and departmental rates.

What's the risk without a declaration?

A Planning Code offence: the town hall can impose regularisation, even demolition, plus fines. Better to file a prior declaration (reply within a month, tacit approval if no answer).

Can the PLU add rules?

Yes. The local plan can impose distances from boundaries, a maximum height or appearance constraints. In a protected area (monument, classified site), authorisation is required even under 5 m².

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