How Do I Write a Lease Addendum?

A lease addendum is a written amendment to a lease that becomes part of the original agreement once both parties sign it. Use one any time the terms change after move-in or when you want to lock in a specific agreement without rewriting the whole lease. Common examples include a new pet being approved, a temporary change to the rent or move-out date, an agreement about lawn care or parking, or a written reminder of a house rule both sides confirm in writing.

Do not change a lease by text message, email, or handshake. Pennsylvania courts enforce the written lease, and a verbal promise about a pet or a rent change is hard to prove and easy to dispute. An addendum gives the change the same weight as the lease itself.

An addendum also protects you by documenting what the tenant agreed to. If you have always allowed the service person access but never in writing, or the tenant says you waived the pet policy, the signed addendum is the record that settles the argument.

Every addendum needs six basic parts: the parties, the property, the original lease, the change, the effective date, and signatures. Reference the original lease by date and property address, and say that everything else in the lease stays the same. The addendum should state one clear change, not a list of unrelated items, so neither side can later say they misunderstood what was agreed.

Write in plain language. Say exactly what changes and when it takes effect, and whether it ends on a specific date or continues for the rest of the tenancy. If the addendum changes money terms, such as a rent credit or a fee, state the amount and how it will be applied. If it adds a rule, state the rule and the consequence for breaking it, consistent with the lease's violation language.

Careful wording matters. A clause that says the tenant agrees to install a window AC unit should also say who pays for it and who is responsible for maintaining it. Ambiguity is where arguments start, so spell out the details even when they feel obvious.

An addendum is only as strong as its signatures and its consistency with the law. Both the landlord and every tenant on the original lease must sign and date the addendum, and each side should receive a copy. An addendum signed by only one roommate binds only that roommate, which creates problems when you try to enforce it against the other.

Keep the addendum consistent with Pennsylvania law and with the lease. An addendum cannot waive a tenant's warranty of habitability rights or require a security deposit above the legal limits. It also cannot override fair housing protections: a rule that targets a protected class, such as banning children or families with a certain national origin, is unlawful no matter how it is written.

If the addendum changes the lease's financial structure, such as converting a fixed term to month-to-month, double-check the deposit and notice rules that apply to the new arrangement. Attach the signed addendum to the original lease and keep both together in your records for the life of the tenancy.

Having a few standard addenda prepared in advance saves time and keeps enforcement consistent. A pet addendum can document an approved pet, its type and size, and the agreed pet deposit or rent. A parking addendum can assign specific spaces and rules for guests. A utility addendum can record who pays each bill when the arrangement changes mid-tenancy.

A move-in condition addendum, often combined with photos or a checklist, records the state of the unit when the tenant takes possession. That document is your evidence if a security deposit dispute comes later. An early termination addendum can formalize an agreed move-out date and the fee or condition attached to it, turning a potential breach into a signed agreement.

For anything that changes the core lease terms, such as rent, consider using a separate amendment that explicitly says it modifies the original clause. Kept clean and consistent, addenda extend the life of your lease without the work of rewriting it, and they give you a complete paper trail for every agreement you make.