When transferring fee simple ownership in real property, Idaho law requires that the property description precisely describe the property. If not, the transfer is not valid. A much more lenient standard, however, applies to the conveyance of easements. If a document granting an easement does clearly and precisely define the easement location, the easement is often referred to as a “floating easement” or a “blanket easement.” These types of easements are not invalid.
In Idaho, a floating easement—or an easement grant without a definite location—it valid and becomes definite and fully defined by its initial use. For instance, in Manning v. Campbell, a written easement allowed the use of an unbuilt driveway “from the end of North 21st street of the city of Boise, Idaho, in a northerly and southerly direction, far enough to allow the [parties] to enter upon their premises.” This 1952 grant neither specified the exact location of the driveway nor its dimensions. About fifty years later, the driveway had been built, but the location and width of the easement became an issue of controversy. The Manning Court explained that the actual construction of the driveway fixed the location and width of the easement. In so doing, it supported the general rule that the initial selection of a place for an easement fixes its physical location.
Throughout the United States, state courts have generally held that once a floating easement is established through initial use, it cannot be unreasonably enlarged or relocated without the servient estate’s consent. (The servient estate is the party who granted the easement and who is burdened by the easement.) To my knowledge, no Idaho court has stated this principle in the context of floating easements, but it is a common principle under the law of easements, so it almost certainly applies to floating easements in Idaho.