Signing the Flatshare Agreement: When and How to Do It

Drafting a flatshare agreement is one thing; signing it at the right time is another. You still need to know when it should be signed, by whom, and what happens to the document once the flatshare's make-up changes along the way.

Signing Before or With the Lease

In Brussels, under the legal flatshare regime, the agreement must be signed at the latest by the time the lease is signed. This is not a best-practice recommendation: it is a condition for benefiting from that specific regime (Brussels Housing Code, art. 2 §1 35°).

In other words, the agreement is prepared upfront, alongside the lease — not "whenever there is time" once everyone has moved in.

Who Needs to Sign

All flatmates covered by the agreement must sign it. The landlord, for their part, is not a signatory to the agreement: they may be aware of it as part of the flatshare lease, but they are not a party to it.

Signing an Agreement Even Without the Legal Flatshare Regime

You do not need to wait for a new lease to formalise things. If you are already a tenant and you are taking in a flatmate, you can draft an agreement at any time to organise the split of rent, charges and house rules.

This document does not have exactly the same status as the "official" agreement provided for under the legal flatshare regime — which assumes the landlord's consent and a joint lease. But it remains legally valid between you, and just as useful for avoiding conflict.

What Happens When a Flatmate Moves Out or In

A change of flatmate alters the make-up of the signatory group: someone who never signed moves in, or someone who did sign moves out.

The best approach is then to sign an amendment — a new version of the agreement — approved by all flatmates concerned, including the new arrival. That way the document stays true to reality, and everyone knows exactly what they have committed to.

Why an Agreement That Is Not Kept Up to Date Loses Its Value

An agreement that no longer reflects who actually lives in the property, or that still lists old shares, becomes hard to rely on the day a disagreement arises. People will argue it no longer matches reality — and they will be right.

Keeping the agreement up to date with every change is therefore not an administrative formality: it is what keeps it useful. A living document is worth infinitely more than a perfect but outdated one.

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