What Is an Unauthorised Construction?
An unauthorised construction is any structure or change of use that was built without the required building permit, or in violation of the permit's specifications. This includes additions, extensions, internal reorganisations, and even change of use (for instance, converting a residence into an office) without proper approval.
In everyday use these are often called illegal building works, and English-language property searches usually use that phrase. The Greek legal term is αυθαίρετο, which this guide renders throughout as unauthorised construction. The two mean the same thing.
At the time of writing, Greek law categorises unauthorised work to guide municipalities and engineers in managing it. It is not uncommon in the Greek construction landscape, particularly in areas with a history of informal building.
Categories of Unauthorised Buildings Under Law 4495/2017
Law 4495/2017 establishes five categories of unauthorised constructions, each with distinct criteria and consequences:
Category 1: Minor Deviations
Small departures from approved drawings or minor constructions affecting a small area. These are considered the least serious and may be eligible for straightforward regularisation.
Category 2: Medium-Severity Unauthorised Work
Unauthorised constructions that exceed small deviations but do not pose serious structural risks. They require detailed investigation and verification of code compliance.
Category 3: Large-Scale Unauthorised Constructions
Substantial additions, extensions, or complete structures built without a permit. These demand thorough structural review and assessment of compliance with building regulations.
Category 4: Unauthorised Work with Special Characteristics
Constructions that may require special studies, such as work in sensitive zones or buildings with historic significance. Regularisation may be more complex.
Category 5: Dangerous Unauthorised Work
Constructions that pose serious risks to public safety, structural integrity, or the environment. These cannot be legalised and typically must be removed.
Regularisation vs Legalisation: What's the Difference?
Two terms often confused, with distinct legal outcomes:
Regularisation
Regularisation is the formal declaration and registration of unauthorised work with the municipal authority. It suspends or reduces enforcement action (fines and removal orders). It does not make the structure fully compliant with current law, but it creates a legal record and protects you from further municipal prosecution.
Legalisation
Legalisation is the issuance of a retroactive building permit that brings the structure into full code compliance. It can only be granted if the unauthorised work meets current zoning and structural standards. Category 5 works cannot be legalised under any circumstances.
In many cases, a structure can be regularised but not legalised, especially if it conflicts with zoning requirements or building codes.
How to Declare an Unauthorised Building: Step by Step
Step 1: Engage a Licensed Engineer
Start by hiring a licensed engineer who is qualified to prepare unauthorised-work declarations. The engineer will inspect the structure, classify it, and prepare the necessary documentation.
Step 2: Technical Documentation and Photography
Your engineer will compile a detailed report with photographs, drawings, and a description of the unauthorised work. They will also gather property deeds and any available information about when the work was done.
Step 3: Classification and Assessment
Based on the evidence, the engineer and municipal authority will classify the work into one of the five categories. This determines the next steps and any associated penalties.
Step 4: Submit the Declaration
The engineer submits the declaration electronically to the competent municipal department. Most submissions today happen via digital platforms managed by local building authorities.
Step 5: Payment of Any Fine (If Required)
If a fine applies, the municipality will notify you of the amount and payment terms. Payment does not erase the fine but may allow for instalments and prevents further enforcement.
Step 6: Official Registration
Once the declaration is accepted and any fine is paid, the unauthorised work is officially registered. This protects you from further municipal action regarding that specific structure.
What Determines the Fine?
Fines for unauthorised work are not fixed. Multiple factors influence the amount:
- Category: Category 1 work incurs lower fines; Category 4 and 5 work incurs higher fines.
- Size: The area of the unauthorised construction directly affects the fine. Larger constructions result in higher penalties.
- Location: Work in central urban zones typically carries higher fines than work in suburban or rural areas.
- Age: Newer unauthorised work generally incurs higher fines. Older work may have lower fines due to partial statute limitations.
- Additional Factors: Local property values, infrastructure availability, and market conditions may influence the calculation.
Regularisation does not eliminate the fine but may allow for graduated payment. An exact figure requires evaluation by your engineer and the local authority.
Current Deadlines and Extensions
Deadlines for declaring unauthorised buildings are not static in Greece. As of this writing, extensions have been granted, and some deadlines are reported to extend to 2028.
However, you should confirm these deadlines with your engineer and local authority, as Greek law can introduce new deadlines or extensions with short notice. Legislative changes may alter the window available to you.
Unauthorised Constructions and Property Transfer
The presence of unauthorised work affects your ability to sell or transfer a property. If you plan to sell, the buyer must be informed, and this may reduce the property's value or affect the transaction timeline.
Many banks require regularisation or legalisation before granting a mortgage on a property with unauthorised constructions. Before any property transfer, issuing a Building Identity Certificate is advisable. This document reveals unauthorised work and protects both parties by providing a transparent record.
Category 5 Unauthorised Buildings
Category 5 unauthorised constructions are exceptional and deserve special attention. These are structures that pose immediate risks to public safety, structural stability, or the environment. Examples include buildings without proper foundations, constructions on landslide-prone slopes, or structures that breach environmental regulations.
Category 5 work cannot be legalised. Instead, the municipality typically issues a removal order. Regularisation in this case documents the structure but leads to mandatory demolition or extensive remedial work.
Working with Premier Construction
Managing unauthorised buildings is technically complex and requires deep knowledge of Greek regulations and local procedures. Premier Construction brings over a decade of experience in regularising and legalising unauthorised work across Greece, with particular expertise in Attica and sensitive zones.
We offer end-to-end services: structural assessment, study preparation, liaison with municipal authorities, and coordination with legal counsel if needed. Our goal is to simplify the process and minimise your legal and financial exposure.
To learn more about our study services or to discuss your property, contact us today.
Frequently Asked Questions
What is the legalisation of unauthorised buildings?
Legalisation is the process of declaring and registering unauthorised constructions or space-use changes that were carried out without the required permit. The declaration is submitted to the relevant municipal authority through a licensed engineer and may be subject to a fine depending on the category of the unauthorised work.
What is the difference between regularisation and legalisation?
Regularisation is the formal declaration and registration of an unauthorised structure, primarily aimed at suspending further enforcement action. Legalisation is the issuance of a retroactive building permit that brings the structure into full compliance with building codes. Regularisation can occur without legalisation in cases where the structure does not meet current requirements.
How long do I have to declare an unauthorised construction?
Greek law sets specific deadlines for declaring unauthorised buildings. As of now, extensions have been granted, with some deadlines reported to reach 2028. We strongly recommend confirming the current deadline with your engineer and the local authority, as deadlines change with legislative updates.
Can I sell a property with unauthorised constructions?
Yes, you can sell a property with unauthorised work, but the buyer must be informed of its existence. Banks often require regularisation before advancing a mortgage on the property. Issuing a Building Identity Certificate before transfer is advisable to prevent future disputes and to provide transparency to the buyer.
How is the fine for unauthorised construction calculated?
The fine depends on several factors: the category of the unauthorised work (1 to 5), its size, the zone (central, suburban, or rural), the age of the construction, and other local criteria. Regularisation does not eliminate the fine but can result in graduated payment terms. Consult your engineer and local authority for exact figures.
What documents do I need to submit for a declaration?
You will need an engineering report, photographs of the unauthorised work, property ownership documents, and information about the construction date if available. Your engineer will prepare the necessary declaration and submit it electronically to the relevant municipal department.
Can all unauthorised constructions be legalised?
No. Category 5 unauthorised buildings, which pose risks to public safety or structural integrity, cannot be legalised. Some unauthorised works may be incompatible with zoning regulations or building standards and may require demolition. A structural and administrative assessment is essential.
What happens if I do not declare an unauthorised building?
Undeclared unauthorised work may result in enforcement action, fines, demolition orders, or legal proceedings initiated by the municipality or third parties. Declaring it protects you by suspending such action and creating a legal record of the situation.
Sources: gov.gr · Law 4495/2017 (kodiko.gr)
Written and reviewed by the engineering team at Premier Construction. Last updated: 24 July 2026. This article is for general information only and does not substitute for professional engineering or legal advice on a specific property. Meet our team.