The Charleston Lowcountry, across Charleston County. Each town below has its own permit authority and its own housing stock, and both change what the work involves.
Where the water goes when the ground will not take it.
Much of this region sits close to sea level with a correspondingly high water table, which means drainage here is not about moving water away quickly — it is about finding somewhere it can actually go.
Most standing water turns out to be a downpipe discharging at the foundation or ground that has stopped falling away from the house. Both are cheaper to correct than to drain around, and both get eliminated before a system is designed.
Most drainage advice assumes fall. Close to sea level, with a high water table and very little fall to work with, collecting water is the easy half and finding somewhere it can arrive is the hard one. A gravel-filled trench discharging into ground that is already at capacity is a trench full of water. So the discharge point is settled before anything is dug, and where there is no gravity outlet the design becomes a sump, a pump, a float and a discharge route rather than a pipe.
Before any of that, three cheaper causes get eliminated, because between them they explain most standing water in the city: downpipes discharging at the foundation instead of away from it, ground that has stopped falling away from the house after years of settlement and mulch, and a hard surface that redirects run-off without anyone intending it. Correcting those costs a fraction of a system, which is why the honest answer to "do I need a french drain" is often no.
Drainage is the division where the building permit is often not the relevant approval. The City of Charleston issues building permits for addresses inside the city, but what usually governs a drainage design is local stormwater and land-disturbance regulation, floodplain rules where the property is in a mapped flood hazard area, and — on a property fronting tidal water — critical area permitting from the Bureau of Coastal Management at the South Carolina Department of Environmental Services.
So the first question on a drainage job is not what will be built but what governs the parcel. Where water is allowed to go is not a design detail; it decides whether the design is legal.
Often not a building permit, but frequently something else — stormwater, land disturbance, floodplain, or critical area permitting if the property fronts tidal water.
Which of those applies is established for the parcel before a design is committed to.
Somewhere lower that is not already wet, and not onto a neighbour, into a wetland or into a storm system without the right approval.
On flat ground with a high water table that is the whole design question, and it is answered before digging rather than after.
Only if the water is arriving from outside. A crawl space that is damp because humid air is condensing in it is a different problem entirely.
The two are constantly confused, and solving the wrong one is expensive.