On some houses rain flows off the main roof and then hits a lower roof before running off to the ground. Where it hits the lower roof it can splash back slightly and get the siding wet where it meets the lower roof. If its wood siding it can stain over the years and you cant wash off that stain if its gotten in the wood.
If you replace the siding with cement siding will water be able to stain that also??? or do people use additional coats of paint on those bottom layers so water cant get in the cement siding..