A lease can be amended by addendum after signing
Yes, a lease can be amended after signing through a written addendum signed by all parties. The addendum modifies, adds, or removes clauses from the original lease. It must be registered with the FPS Finance. Amendments cannot contravene public order provisions such as minimum lease duration, indexation rights, or rental deposit caps.
The principle of contractual freedom (Article 1134 of the Civil Code) allows parties to modify a contract by mutual agreement at any time. An addendum to the lease is a legal document that becomes an integral part of the original contract.
The addendum must be signed by all parties to the lease: if there are two landlords, both must sign. Similarly, if the lease is a colocation with three co-tenants, all must consent to the modification.
No party can unilaterally impose an amendment. If the landlord wishes to change a clause and the tenant refuses, the lease remains unchanged. Recourse to the justice of the peace is only possible in specific cases provided by law (e.g. rent revision).
How to draft an addendum
The addendum must contain:
- Reference to the original lease — date, address, identity of parties
- Subject of the modification — precise description of the clause being changed
- Former wording — the exact text of the clause being modified
- New wording — the replacement text
- Effective date — when the modification takes effect
- Signatures — all parties to the lease
Common amendments:
| Amendment | Addendum required? |
|---|---|
| Rent change (beyond indexation) | Yes |
| Adding a co-tenant | Yes |
| Duration change | Yes |
| Bank account change | Yes (recommended) |
| Allowing a pet | Yes |
| Annual indexation | No (provided by law) |
Generate your addendum via BailBelgique: the system retrieves the original lease information and offers a legally compliant addendum template. Electronic signature is available for all parties.
Legal limits on lease amendments
Certain amendments are prohibited as they contravene public order provisions:
- Reducing duration below the legal minimum — you cannot convert a 9-year lease into a shorter one mid-term
- Exceeding rental deposit caps — the addendum cannot increase the deposit beyond the legal maximum (2 or 3 months depending on the region)
- Waiving the tenant’s right to terminate — the tenant cannot give up their right to early termination
- Removing the inventory obligation — this obligation is a matter of public order
- Retroactive waiver of indexation — future waiver is possible, but not retroactive
The addendum must be registered with the FPS Finance within 2 months of signing, like the original lease. Registration is free for primary residence leases. An unregistered addendum remains valid between the parties but cannot be enforced against third parties.
A simple exchange of emails or verbal agreement does not constitute a valid addendum. The amendment must be formalised in a written document signed by all parties to be enforceable before the justice of the peace.
Regional specifics
Brussels-Capital Region
The ordinance of 27 July 2017 does not contain specific provisions on addenda. General contractual freedom principles apply. In Brussels, addenda are frequently used to add or remove co-tenants in colocation arrangements.
Walloon Region
The decree of 15 March 2018 requires that any lease modification respect the decree’s mandatory provisions. The addendum must be registered via MyRent.
Flemish Region
The Vlaams Woninghuurdecreet of 9 November 2018 allows addenda subject to compliance with mandatory provisions. In Flanders, the addendum can be drafted in Dutch or French if both parties understand the language, but Dutch is recommended for registration.
Civil Code, art. 1134 (contractual freedom, modification by mutual agreement). Regional housing legislation on mandatory lease provisions. Addenda must respect public order provisions.