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Lease glossary

Lease addendum

A lease addendum is a separate, signed document that adds terms to a lease or changes existing ones, and becomes part of the lease once both sides sign it. Common addendums cover pets, parking, smoking, a new roommate, or a change to the rent or the end date.

Also called addendum · lease rider

Example

Six months into a 12-month lease at $1,500 a month, a tenant adopts a dog. On April 1, 2026 the landlord and tenant sign a pet addendum that names the dog, adds a $300 refundable pet deposit and adds $35 a month in pet rent. From April the tenant pays $1,535 a month. The rest of the lease is unchanged, and on anything to do with the dog, the addendum governs.

In a lease it looks like…

This Pet Addendum is part of the Lease dated October 1, 2025. Tenant may keep one dog, Juno, at the premises, and shall pay a refundable pet deposit of $300 and pet rent of $35 per month beginning April 1, 2026. Where this Addendum conflicts with the Lease, this Addendum controls.

Good to know

An addendum binds only the people who sign it, so every tenant on the lease should sign. Some addendums are required rather than optional: federal law requires a lead-based paint disclosure for most housing built before 1978, and many leases attach it as an addendum.

Plain English, not legal advice. Last reviewed September 29, 2026.