This is in Pennsylvania.
In the 1909 land "atlas" no structure is shown on these 20 acres.**
By 1916 two houses appear in the old maps. They are 300 yards apart.
The one here in issue was built on a level lot--which was apparently made level by digging out what was a moderate hillside. Retaining walls were apparently built at the rear and on two sides of the property.
Later (1930s) many houses were built, and lots divided, re-divided, and sold.
There are now three houses bordering on this house and lot.
The one in back is on a fairly level lot about 20 feet higher than this lot, which runs right up to the retaining wall. Then it is 20 feet straight down.
1. If the retaining wall needs repair, who must pay for it?
And who decides when that is needed--or must we await collapse?
2. What if the owner behind (and 20 feet higher) allows a condition--a small tree growing at the edge--which he has been notified by an expert may cause the collapse of the retaining wall and fails to remedy it?
3. The tree can be removed for a few hundred dollars.
Can the owner below get a court order requiring the owner above to remove the tree?
**A few more "facts". The house in issue may have incorporated some part of a much older structure--some say a mill was here. No clear evidence yet.
The adjacent houses--on two sides--retain some hillside in back and thus have no retaining walls. A couple of others on the street do have retaining walls and were apparently also dug out.
The present owner of the subject house has owned it for over fifty years.