In Belgium

A private agreement (acte sous seing prive / onderhandse akte) is any legal document drafted and signed by the parties without a notary’s involvement. In Belgian property law, it is the standard form for:

  • Leases: a lease does not require a notary — a signed agreement between landlord and tenant is sufficient
  • Sale compromises: the initial sale agreement is a private agreement, later confirmed by an authentic deed
  • Addenda to leases: modifications to an existing lease

How it works

Legal force. A private agreement is binding between the parties who signed it. It has probative value (it proves its content) but not enforceable force (unlike a notarial deed, it cannot be directly enforced without a court judgement).

Registration. For leases, registration with the FPS Finance is mandatory and free for primary residence leases. Registration makes the lease enforceable against future buyers of the property.

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Good to know
A sale compromise (private agreement) is already legally binding — both parties are committed to the sale. Withdrawing after signing the compromise can trigger a penalty of 10% of the sale price. The subsequent authentic deed confirms and formalises the agreement.

Practical example

Pierre and his landlord sign a private lease agreement for a 2-bedroom apartment at 750 EUR/month. No notary is involved. The lease is registered at the FPS Finance (free for primary residence). When the building is sold 3 years later, the new owner must respect Pierre’s lease because it was registered.