Tenancy Agreement Addendum: How to Vary Terms During a Tenancy

What changed under the Renters' Rights Act 2025

Section 21 abolished. Fixed-term assured tenancies abolished. Ground 8 threshold raised to 3 months. Information Sheet required for every tenancy by 31 May 2026. Read the full guide.

An addendum is still the standard way to add or change a term of an existing tenancy without tearing up the original agreement — but the mechanics shifted on 1 May 2026. This guide sets out what an addendum is, when landlords use one, what has to happen for it to be legally binding, and how it now fits around the periodic-tenancy system introduced by the Renters' Rights Act 2025.

What is a tenancy agreement addendum?

An addendum is a short, separate written document that adds a new term to an existing tenancy agreement — for example a permitted-occupier clause, a parking condition, or an updated address for service. A variation changes a term that is already in the agreement, such as loosening a no-pets clause. Both work the same way in practice: the original tenancy agreement stays in force, and the addendum or variation is read alongside it as part of the same contract.

This is different from issuing a brand-new tenancy agreement, which ends the existing contract and starts a fresh one. Landlords sometimes reach for a new agreement out of habit, but it is rarely necessary just to add or change a term — and doing so can have knock-on effects (a new deposit protection cycle, a new "How to Rent" guide requirement, and a reset of the tenancy's history) that an addendum avoids.

There is one technical wrinkle worth knowing: under long-standing land law principle, a variation that is significant enough — for example one that changes the property let, or effectively ends one tenancy and starts another — can be treated in law as an implied surrender and regrant of the tenancy, even where both parties only meant to tweak a clause. The Renters' Rights Act 2025 recognises this. Section 12 of the Act (inserting section 16D(1) of the Housing Act 1988) specifically excludes a tenancy that arises this way — an implied surrender and regrant resulting from an agreement to vary the previous tenancy's terms — from the fresh written-statement-of-terms duty that otherwise applies to new tenancies. In practice, most routine addendums (adding a person, a pet, a parking space, a contact detail) do not go anywhere near this territory, but it is the reason significant restructuring of a tenancy's terms is best done carefully, and with proper records.

When landlords use an addendum

Common mid-tenancy scenarios include:

• Adding a permitted occupier — recording that someone new is entitled to live at the property alongside the named tenant.
• Parking or storage — adding a right to use a parking space, garage, or garden shed that wasn't in the original agreement.
• Updated contact or service details — recording a new landlord address for service of notices, or a new emergency contact.
• Smoking or lifestyle clauses — tightening or relaxing a no-smoking condition by agreement.
• Guarantor arrangements — adding a guarantor's obligations partway through a tenancy (this is one of the situations where formal execution matters — see below).

Pets are the one common exception. Since 1 May 2026, every assured tenancy carries an implied statutory term under section 16A of the Housing Act 1988 (inserted by section 11 of the Renters' Rights Act 2025) giving tenants the right to ask, in writing, to keep a pet. The landlord must give or refuse consent in writing within 28 days (longer in limited circumstances) and cannot refuse unreasonably. This is a statutory consent process, not a discretionary addendum — a landlord cannot simply decline to add a "pets allowed" clause. Recording the landlord's consent in writing is still good practice and can sit alongside the tenancy as a short side letter, but it documents a statutory right rather than negotiating a new term from scratch.

Rent increases are not done by addendum. Since the same date, section 13 of the Housing Act 1988 (as amended by section 6 of the Renters' Rights Act 2025) makes the statutory Section 13 notice procedure — or a rent tribunal determination — the only route to increase rent on a private tenancy. Any addendum, side letter, or rent-review clause purporting to raise the rent by private agreement has no legal effect. The one exception is agreeing a lower rent than a Section 13 notice proposed.

Legal requirements for a valid addendum

For an addendum or variation to be enforceable:

• Both parties must agree. Section 13(4B) of the Housing Act 1988, inserted by the Renters' Rights Act 2025, expressly preserves the landlord and tenant's right to vary a tenancy term "by agreement" — meaning mutual consent, not unilateral imposition. A landlord cannot vary the tenancy by simply notifying the tenant, and neither can a tenant.
• Put it in writing and get it signed and dated by both parties. This isn't always a strict legal requirement for every type of change, but it is the only practical way to prove what was agreed if a dispute arises later.
• Reference the original tenancy. State the date of the original tenancy agreement, the property address, and the names of the parties, so the addendum is clearly tied to the tenancy it amends.
• Deeds are the exception, not the rule. Under section 52 of the Law of Property Act 1925, conveyances of an interest in land generally need a deed — but section 54(2) carves out leases (and, by extension, most residential tenancies) taking effect for a term not exceeding three years at the best rent reasonably obtainable. Most ASTs and the periodic tenancies that replaced them fall into this exception, so an ordinary written and signed addendum is normally sufficient. A deed becomes relevant mainly where a change extends the term beyond three years, formally adds a guarantor's covenant, or creates a fresh interest in the land.
• Keep a copy with the tenancy file. Both parties should retain a signed copy alongside the original tenancy agreement, so the full, current set of terms is always available if the tenancy is ever queried or challenged.

Addendums after the Renters' Rights Act 2025

From 1 May 2026, new tenancies (and existing ASTs that rolled over) became periodic assured tenancies with no fixed term to renew or "vary" in the old sense. That does not stop landlords and tenants adding or changing terms — section 13(4B) of the Housing Act 1988, inserted by the Renters' Rights Act 2025, expressly preserves "any right of the landlord and the tenant … to vary any term of the tenancy by agreement," and restricts only how rent itself can be increased. In other words: the mechanism landlords have always used — a short written addendum, signed by both sides — still works exactly as before for adding a permitted occupier, updating contact details, or agreeing a parking arrangement. What has changed is the rent-increase route (now Section 13 only) and the pets process (now a statutory 28-day consent procedure rather than something added at the landlord's discretion).

If a landlord issued a written statement of tenancy terms when the tenancy began (a duty introduced by section 12 of the Renters' Rights Act 2025), it is sensible to keep that statement and any addendums together, so the tenant always has one clear picture of what has been agreed and when.

What to include in a good addendum

A well-drafted addendum should cover:

1. The date of the original tenancy agreement and the property address.
2. The full names of the landlord and tenant(s).
3. The specific clause being added or varied, written out in full — not just referenced.
4. The date the change takes effect.
5. Signature and date lines for both landlord and tenant.
6. A short confirmation that all other terms of the original tenancy remain unchanged.

Keeping the addendum short, specific, and tied clearly to the original agreement avoids ambiguity about which version of the tenancy terms applies if a dispute or possession claim arises later.

Using a template

A properly structured addendum template gives you the reference fields, signature blocks, and confirming wording above in a format both parties can complete and sign in minutes, without drafting from scratch each time a term needs to change. Whichever template you use, check it reflects the post-1 May 2026 position on rent increases and pet requests described above — older templates written for the fixed-term AST era may still include rent-review or pet-refusal wording that is no longer effective.

This guide provides general information for landlords in England and Wales and does not constitute legal advice. If a proposed change is unusual — for example it affects a guarantor, extends beyond routine terms, or you are unsure whether it risks an implied surrender and regrant — it is worth getting the specific wording checked before both parties sign.

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For the full library of tenancy paperwork, visit the Legal Documents hub, or start with our Tenancy Agreement guide if you're setting up a new tenancy rather than amending an existing one.