In article ,
Frank wrote:
I have a neighbor who decided to plant an Aristocrat Flowering Pear
Tree about 5 feet from our property line and about 17 feet from my
foundation in highly expansive clay soil that is watered almost year
round: in Califorina where we go long spells without rain. I have
water lines and sprinkler lines within feet of that tree, and a water
line about seven feet from it.

One of my concerns with this tree is potential root damage to my
home's foundation, concrete driveway, and anything I decide to put in
that area in the the future.

You're in luck, then. Pyrus calleryana 'Aristocrat' is very popular
as an urban and street tree, because it's a very attractive undemanding
tree that isn't prone to causing problems with the sidewalks/roads.

It's also very tolerant of variable soil and water conditions.

I've been researching root barriers, and the one idea I'm debating is
putting in a 4 to 6 feet deep (below ground) rebar reenforced concrete
wall along our property line to keep this tree from damaging my
property. Does anyone know how effective root barriers are at
different depths in the soil?
How well would a rebar reenforced below-ground wall work?
Any other ideas for an effective root barrier system?

What is your specific concern here? I notice that you've mentioned
that your soil is watered year 'round, which is fairly unusual in
California - and certainly not particularly mindful of the water
problems in many parts of California. Is there something unusual in
your garden that you think that this tree will bother?

Has anyone ever had any success in taking a neighbor to court for
intentionally planting a tree that they know will encroach on your
land and will likely damage your propery over time?

Actually your neighbour has planted a tree that's very commonly used
in landscaping because it -won't- damage your property over time. It
wolud be very hard for you to make any sort of case in the first place,
and given that the tree in question isn't known to be problematic,
even harder.

Other people have said this in a less friendly way, but it does sound
as though your primary concern here isn't the tree, and what the tree
might do to your property, as much as being able to carry on some sort
of disagreement with your neighbour.

Without having any idea what the issues are [nor quite frankly wishing
to], it might be worthwhile to attempt mediation to resolve whatever
the outstanding issues are.

cheers!
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"A cat spends her life conflicted between a deep, passionate and profound
desire for fish and an equally deep, passionate and profound desire to
avoid getting wet. This is the defining metaphor of my life right now."