The Co-ownership Deed in Belgium: Structure, Content and How to Amend It

Every Belgian co-ownership is governed by a set of foundational documents that define the building's division, the rights and obligations of co-owners, and the rules of daily life. Understanding the structure and hierarchy of these documents is essential — particularly for international owners unfamiliar with Belgian property law.

Base Deed vs Co-ownership Regulations

Belgian law creates a two-tier documentary structure:

The base deed (acte de base / basisakte), governed by Art. 577-3 Belgian Civil Code, is the notarial deed that physically divides the building. It defines:

The description of the building and land.
The division into private lots (apartments, garages, cellars) and common parts (hallways, roof, facade, garden, lift shaft).
The tantièmes (co-ownership shares) assigned to each lot, expressed in thousandths or ten-thousandths.

The co-ownership regulations (règlement de copropriété / reglement van mede-eigendom), governed by Art. 577-4 Belgian Civil Code, is the companion notarial deed that sets out the legal framework for living together. It must contain:

The rights and obligations of each co-owner regarding private and common parts.
The rules governing the general assembly (convocation, quorum, majorities).
The method for distributing common charges (general and special keys).
The criteria and calculation of the tantièmes.
Rules on the syndic's appointment and duties.

Both documents are registered at the mortgage office (bureau de conservation des hypothèques) and bind all current and future owners.

Mandatory Content Under Art. 577-4

Art. 577-4 §1 Belgian Civil Code lists the minimum mandatory content of the co-ownership regulations. Since the 2018 reform, the regulations must also include:

Explicit rules on the use of common parts (parking, garden, laundry room).
Procedures for modifications to the distribution of charges.
A description of the decision-making procedure for works on common parts.
Rules on the maintenance and management of the building archives.

Any co-ownership regulation that omits mandatory content is not void, but the missing provisions are automatically supplemented by the default rules of the Belgian Civil Code.

Internal Rules (ROI)

Alongside the notarial deeds, Belgian co-ownerships may adopt internal rules (règlement d'ordre intérieur / reglement van interne orde), commonly abbreviated as ROI. The ROI covers practical, day-to-day matters:

Quiet hours and noise restrictions.
Pet policies.
Use of common facilities (barbecue area, bicycle storage, swimming pool).
Moving-in/moving-out procedures.
Short-term rental restrictions (e.g., Airbnb limitations).

The ROI can be adopted or amended by simple majority at the general assembly — no notarial deed or mortgage office registration is required. However, the ROI cannot contradict the co-ownership regulations or the Belgian Civil Code. If a conflict arises, the higher-ranking document prevails.

Amendment Procedure

Amending the base deed or co-ownership regulations is a formal and costly process:

GA vote: a four-fifths majority (4/5 of all co-ownership shares) is required for most amendments (Art. 577-6 §11 Belgian Civil Code). Changes to the charge distribution keys require unanimity unless they correct an error or reflect a physical modification of the building.
Notarial deed: the amendment must be formalised by a notary, who verifies that the GA resolution is legally valid and that the required majority was achieved.
Registration: the notarial deed is registered at the mortgage office, making it opposable to third parties and future purchasers.
Cost: notarial fees, registration duties, and mortgage office fees typically total €500 to €2,000, borne by the ACP.

Outdated Regulations

Many Belgian buildings still operate under co-ownership regulations drafted before the major reforms of 1994 and 2010. These outdated documents often contain clauses that are incompatible with current law — for example, unlimited syndic mandates, no reserve fund provisions, or charge distribution methods that ignore the mandatory criteria of Art. 577-4.

In all cases, the Belgian Civil Code prevails over conflicting regulatory clauses. Co-ownerships with pre-2010 regulations should prioritise updating their documents to avoid legal uncertainty and potential disputes before the justice of the peace.

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