The houses in the Back Bay are built almost exclusively with shared side walls, called party walls or partition walls, between them. The walls are usually one foot thick, made of brick, and situated so that they straddle the property line with half on each side.

Because the walls are shared between two lots, when the house were being built, there was a need to clearly establish the responsibility for the cost of building and maintaining the walls.

The deeds of land on the north side of Beacon Street from the Boston and Roxbury Mill Corporation included a provision that “the center of the easterly and westerly partition walls of the houses and buildings first erected on the said land shall be placed on the division lines between the granted premises and the adjoining lots, and shall be good and sufficient walls, and the party first building such partition wall, whether the owner of the premises hereby granted or of an adjoining lot, shall be entitled to have and receive from the party using such wall, one half of the actual cost of so much of said wall, including the pile foundations, and stone or brick work, and fences as he shall actually use” (Book 780, p. 30; 8Jun1860).

By contrast, although they contained extensive provisions limiting the design of the houses to be built, the deeds of land from the Commonwealth of Massachusetts and from the Boston Water Power Company did not mention the party walls. This omission was dealt with in several different ways.

In some cases, when a large tract of lands was acquired, the buyer would include party wall stipulations in the subsequent deeds. For example, when William W. Goddard and T. Lawrence Bigelow sold portions of the land on the south side of Beacon they had acquired from the Commonwealth, they included a stipulation in the deed that “this conveyance is made upon the agreement that the grantee, his heirs and assigns, shall drive the piles and lay the stone foundations and erect thereon a brick partition wall of a character suited for and strength sufficient to sustain a dwelling house of the first class such wall to be placed on half on our adjoining land and we for ourselves and our representatives, agree to pay on demand one half of the cost of such wall or the part or parts thereof as we may use when and as we shall use the same, including in such cost one half of the pile and stone foundations” (Book 811, p. 297; 1Apr1862).

In other cases, individual land owners would enter into party wall agreements with their neighbors prior to beginning construction. These agreements are often a good indication of when a particular building was built, inasmuch as construction usually began soon after the agreements were signed. On some occasions, however, party wall agreements were entered into several years before construction. In the case of 199 Commonwealth, for example, houses had been built at both 197 Commonwealth to the east and 203 Commonwealth to the west when J. Arthur Beebe entered into party wall agreements with both owners on June 25, 1888 (Book 1832, pages 290 and 291). He did not file a permit to begin construction, however, until October of 1890, more than two years later.

The details of individual party wall agreements varied depending on whether the wall was being built for the first time or had already been built as part of an earlier house and was to be used by a later neighboring house. The agreements specified the shared responsibility for paying for the wall and, in some cases, also specified responsibilities for maintaining the wall or making additions or other changes to it.

Not every building had a party wall agreement. For example, there was no need for an agreement governing the walls between buildings built by the same builder at the same time. In such situations, however, subsequent owners occasionally entered into party wall agreements. For example, on December 1, 1923, the owners of 113 Beacon and 115 Beacon entered into a party wall agreement governing the wall between their houses, both of which had been built ca. 1863 by the same builder (Book 4532, p. 244).

Occasionally, a party wall was not built exactly on the dividing line between two properties. In those cases, a special agreement would often be entered into to resolve the situation. The usual solution was for one party to sell a fractional strip of land to the other to correct the condition. For example, when 9 Commonwealth was built, the western party wall was located entirely on the owner’s land, rather than straddling the line between 9 and 11 Commonwealth. To correct this situation, on December 4, 1867, when 11 Commonwealth was about to be built, the owners of the two properties entered into an agreement under which the owner of 11 Commonwealth bought a six inch strip of land and the party wall on it from the owner of 9 Commonwealth so that each property would own one half of the wall.

In some cases party wall agreements dealt with special situations, such as windows that had been installed in the party wall before the neighboring building was built. For example, the owners of 23 Commonwealth had installed several windows in their western party wall, which were not obstructed by 25 Commonwealth because of the design of the latter building. On October 1, 1880, in anticipation of selling 23 Commonwealth, the owner entered into an agreement (Book 1505, p. 386) with the owner of 25 Commonwealth allowing the windows to remain as long as the party to whom she sold continued to be the owner (after 23 Commonwealth changed hands again, 25 Commonwealth was expanded and the windows in the wall of 23 Commonwealth were removed). This agreement also dealt with an error in the location of the party wall between 23 and 25 Commonwealth which, “by fault of the builders,” had been placed on 4 inches of the property of 25 Commonwealth. Under the agreement, the parties accepted the location of the dividing line as being four inches to the east.

Party wall agreements also often were entered into, or earlier agreements modified, when one party wished to modify or replace the existing structure. For example, on January 27, 1928, as the owners of 172 Beacon were “erecting or about to erect” a new apartment building, they entered into party wall agreements with the owners of 170 Beacon and 176 Beacon (Book 4973, p. 392 and 394).

Although party wall agreements often are limited to specifying the location and sharing of the cost of the original wall, they may also include language governing the right to modify the walls and specifying how the costs of such modifications are to be shared. These agreements may or may not have current effect.

Party wall agreements are sometimes, but not always, referenced in land transfer deeds. Property owners should consult their deeds with the assistance of legal counsel, and should obtain copies of any party wall agreements which may affect their buildings.