In Iowa, the maximum duration of a standard residential lease agreement is one (1) year. Longer leases can exist, but they must be in writing (not verbal).
It is recommended that all rental agreements be in writing. Verbal agreements are enforceable, but it is difficult to prove what the landlord and tenant agreed upon.
If the rental agreement does not specify a tenancy duration, the lease is considered month-to-month if rent is paid monthly, or week-to-week if paid weekly (IA Code § 532A.9 (2019)).
The information for this answer was found on our Iowa Residential Lease Agreement answers.