Roof Water
Where should my downspouts drain to?
To a point genuinely lower than the downspout and far enough from the house that water cannot track back through the foundation backfill. On the clay-rich soil common across Chester and Delaware County that is considerably further than most homeowners expect, which is why the underground carrier line is usually the larger part of the work.
In more detail
A splash block moves water a foot or two and relies on the ground to absorb it. On clay the ground does not do that at any useful rate, so the water pools and then follows the path of least resistance — the disturbed backfill against the foundation wall.
The carrier should be solid pipe, not perforated. A perforated carrier leaks along its length and recreates the original problem underground where it cannot be seen.
It needs consistent fall. A line with a sag holds water, and a line holding water in December freezes, blocks and backs up to the downspout. Rigid smooth-wall pipe is preferable to corrugated flexible tubing, whose interior traps sediment and which is easy to lay with unintended dips.
Where the property has no fall to a usable release point, the honest options are a dry well sized for the contributing roof area or a pumped system. There is no arrangement in which water runs uphill.
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