What part of a outdoor staircase will rot first?

Question

answers to chose from:

1. hand rail

2.bottom of stringer

3. tread

4.top step

Answer 1

Sods Law says the most expensive part to repair/replace. .........

Answer 2

if your doing a scientific experiment you're doing it poorly.  I would say non of the above.  You certainly haven't given this group enough information.  If everything is as its supposed to be, water treatment, etc., then none of these will rot.  Its only when you're careless and just let stuff go.

Answer 3

Bottom of stringer if on ground.Otherwise any untreated or un paint protected part.