Interior drain tile vs. exterior footing drain retrofit: decision workflow

Steps

1. Diagnose the actual water pathway first: interior drain tile manages hydrostatic water rising under/through the slab and wall-floor joint; exterior footing drains intercept water before it reaches the wall by directing it at the footing level to daylight, a dry well, or storm connection — the two solve different failure modes, so start with a leak-pattern diagnosis before choosing.
2. Weigh access and disruption: exterior excavation on an existing structure is typically far more disruptive (landscaping, hardscape, utilities, tight lot lines) than an interior perimeter-trench retrofit — this cost/disruption gap usually drives the practical decision when both are technically viable.
3. Prefer exterior where feasible: it stops water before it enters the wall assembly, keeping the wall itself dry; interior systems only capture water after it has already passed through/under the foundation.
4. Confirm the retrofit has a legal discharge path (gravity daylight, dry well, or a sump discharging per local rules) — a drain tile system without a compliant outlet just relocates the problem to a pump.
5. For severe hydrostatic conditions or high water tables, consider specifying exterior waterproofing/footing drain together with interior drain tile and a sump rather than treating this as a strict either/or choice, and ground the underlying waterproofing trigger in IRC R406 rather than treating it as purely a cost decision.