When a French drain actually helps (and when it does not)
Pipe in clay only works with slope and an outfall. A trench with no fall is a hidden pond.
A French drain is a sloped pipe in rock, wrapped so fines do not choke it, daylighting to a place water is allowed to go. It is not a magic sock you bury along a foundation and hope the clay cooperates.
In Plano, Allen, and established Dallas lots, the failure mode is almost always the same: the drain is too flat, the outfall is the neighbor, or the yard is a bowl and nobody wanted to regrade. Trinity Land and Excavation will tell you when the honest fix is six inches of dirt moved, not forty feet of pipe.
Downspouts belong in the system. A beautiful drain that still receives roof water at the slab is a decorative trench. We tie leaders in or we tell you the quote is incomplete.