Party wall easement

Townhouses are, in fact, some of the most common example of appurtenant
easements. Townhouses typically have party walls that straddle the boundary of two separate parcels of property. This situation is governed by a party wall easement, in which each owner owns his or her half of the wall but has an easement over the other half of the wall.

For example, Achilles and Zena own neighboring townhouses that share a party wall. Achilles owns his half of that wall, but he and his property also have a party wall easement over Zena’s half of the wall. Such an easement would prevent Zena from causing any damage to her side of the wall that may affect the party wall as a whole or Achilles’ half of the wall.