Legal Question in Real Estate Law in California

Iif he built the wall on your property [there is no common ground, the abutting property line for both lots is the same line], then use can make reasonable usage of the part on your side, as long as it does not damage the wall. It is unclear to me whether screwing a bolt into the wall falls within reasonable usage as it is putting a hole in the wall. But you probably have the right to remove any part of the wall that is on your property line as long as you do not destroy his portion, so you probably have the right to use the wall by placing the metal into it. Before you do so, speak to your neighbor to work out a settlement; promise to pay if your usage causes damage to his part of the wall [which you are responsible for legally anyway], but he should pay for the damaged bolt [you do not want to appear to be a push over or you become one].

I agree with Mr. Shers' analysis. If the neighbor has built a ten-inch thick stone wall on the boundary, and five inches of the thickness sits on your land, then the wall is either (a)trespassing, or (b) a donation to your property. Either way, the neighbor is on shaky legal ground telling you that you can't affix a latch to it. Confirm as bet you can that the wall is at least in some part over the property line, and give the neighbor the choice of letting you latch to it or moving his doggone wall back on his own land! Try to be friendly about it, of course, but if you point out the absurdity of his position, given the trespassory encroachment, maybe he'll voluntarily back off.

There is also a provision in the Civil Code at section 841 regarding the shared responsibility of neighbors for boundary fences (which would include walls), but it is written so that it only applies to cases where a neighbor encloses his entire property. It is an 1872 law and was written with the needs of crop growers to separate their property from livestock growers.