An appurtenance refers to something that, while technically detachable, is so fundamental to something else that it should be regarded as a part of the whole. In the event that property transfers hands, all appurtenances usually transfer as well. Determining whether something qualifies as an appurtenance is especially important when liens on property are at play.
For example, while a ship can still technically sail without radar systems, an installed radar system would qualify as an appurtenance to the ship it's installed in. In the event the ship is seized per a lien, the radar system would transfer along with the ship. Other examples include swimming pools, water heaters, kitchen cabinets, or other things a party would expect to transfer when the property exchanges hands.
Something can be appurtenant even if it is not attached to the primary property at the time of transfer. In Stewart & Stewart v. Stevenson for example, two propellers and two tail shafts which were not yet attached to the ship in question were still considered appurtenant because they were bought with the intention of installing them in the ship.
The term appurtenant also appears in the context of appurtenant easements, or easements that attach to land. Much like appurtenant property, these easements transfer if the attached property does.
[Last updated in June of 2022 by the Wex Definitions Team]