Exterior drains run along the outside of the foundation footing and are installed before the soil gets backfilled. They are the standard call for new construction homes and most commercial projects.
Interior drains run just inside the foundation wall and are the go-to for retrofits, basement finishes, and renovations where the exterior is already buried. Common in older homes, schools, offices, and multi-unit buildings being brought up to current standards.
Both systems do the same thing: collect groundwater into a perforated pipe bedded in washed gravel, slope it toward a sump pit, and let the sump pump kick it out and away from the structure.
Drain pipe has to sit below slab level, at the base of the foundation footing. That is where the water gets intercepted before hydrostatic pressure builds against the wall. In commercial structures, that pressure can shift the slab enough to disrupt mechanical systems and interior build-outs. In a basement, it shows up as water on the floor.
Perimeter drainage does not work in isolation. It connects to the waterproofing on the wall, the drainage board protecting that waterproofing, the vapor barrier under the slab, and the aggregate base everything sits on. We install the full stack on the same project, on the same schedule, with one accountable contact.
For the aggregate base under your radon piping, see also: Under Slab Radon Rock & Gravel