Encroachment takes place when any part of buildings or other structures of a landowner extend beyond the boundaries of his/her land to the adjoining land.  When the land owner has a right of easement or by agreement, then there is no encroachment.  In common law, continuing encroachment by a land owner upon the land of another by erecting and maintaining a building thereon without right is a private nuisance[i].  The courts regard encroachment as nuisance[ii].  In Boyle v. Neisner Bros., Inc., 230 Mo. App. 90 (Mo. Ct. App. 1936), the court held that nuisance is anything that works hurt, inconvenience or damage.  The court further held that a permanent encroachment on a public street for a private use is a nuisance.

Generally, for maintaining an action for encroachment the courts do not make a difference whether it was done intentionally, or was the result of negligence[iii].  In Milton v. Puffer, 207 Mass. 416, 418 (Mass. 1911), the court held that projecting the stones into the adjoining land without a right or license from the owner to do so is a nuisance.

[i] Hanlin Group, Inc. v. International Minerals & Chemical Corp., 759 F. Supp. 925 (D. Me. 1990)

[ii] Norwalk Heating & Lighting Co. v. Vernam, 75 Conn. 662 (Conn. 1903)

[iii] Clark v. Springfield, 241 S.W.2d 100, 108 (Mo. Ct. App. 1951)