Short answer. Article 660 lists seven exterior signs that rebut the party-wall presumption — among them a window in the dividing wall, the wall sitting entirely within one estate, one side alone bearing the roof or floor beams, and an enclosed lot adjoining an unenclosed one. Any one of these signs alone shifts ownership to a single neighbor.
What the law says
Whenever in the dividing wall of buildings there is a window or opening
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
What the law says
Whenever the dividing wall is, on one side, straight and plumb on all its facement, and on the other, it has similar conditions on the upper part, but the lower part slants or projects outward
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
What the law says
Whenever the entire wall is built within the boundaries of one of the estates
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
What the law says
Whenever the dividing wall bears the burden of the binding beams, floors and roof frame of one of the buildings, but not those of the others
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
What the law says
Whenever the dividing wall between courtyards, gardens, and tenements is constructed in such a way that the coping sheds the water upon only one of the estates
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
What the law says
Whenever lands inclosed by fences or live hedges adjoin others which are not inclosed.
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
What the law says
In all these cases, the ownership of the walls, fences or hedges shall be deemed to belong exclusively to the owner of the property or tenement which has in its favor the presumption based on any one of these signs.
Civil Code, Article 660 — Exterior Signs Against a Party Wall. Read the full provision →
A window or an uneven wall face
Article 660 treats two features of the wall's own construction as signs against the party-wall presumption. The first is straightforward: whenever in the dividing wall of buildings there is a window or opening, that alone counts as an exterior sign. The second looks at the wall's profile: whenever the dividing wall is, on one side, straight and plumb on all its facement, and on the other, it has similar conditions on the upper part, but the lower part slants or projects outward, that asymmetry is likewise treated as a sign against shared ownership. A third sign involves masonry stepping stones projecting from only one face of the wall at intervals, rather than both.
Where the wall sits, and what it carries
Two further signs look past the wall's surface to its footprint and structural role. Article 660 counts it as a sign whenever the entire wall is built within the boundaries of one of the estates, rather than straddling the property line. It similarly counts as a sign whenever the dividing wall bears the burden of the binding beams, floors and roof frame of one of the buildings, but not those of the others — meaning only one structure is actually resting its weight on the wall.
Drainage and enclosure as signs of sole ownership
Article 660 also looks at how water is shed and how land is fenced. It is a sign against the party-wall presumption whenever the dividing wall between courtyards, gardens, and tenements is constructed in such a way that the coping sheds the water upon only one of the estates. Separately, outside the context of walls specifically, the same rule extends to land: whenever lands inclosed by fences or live hedges adjoin others which are not inclosed, that difference in enclosure is treated the same way.
What any one of these signs actually does
Article 660 does not require all of these signs to appear together. The article closes by stating that in all these cases, the ownership of the walls, fences or hedges shall be deemed to belong exclusively to the owner of the property or tenement which has in its favor the presumption based on any one of these signs. In other words, a single qualifying sign is enough to shift the presumption away from shared ownership and toward exclusive ownership by whichever neighbor the sign favors.