Match the Solution to the Water Source
Exterior waterproofing (excavation, footing drains, membranes) tackles bulk water before it reaches the wall—ideal for chronic seepage or hillside lots but costly where access is limited. Interior French drains with a sealed sump intercept water at the slab edge; they’re highly effective for hydrostatic pressure and can often be installed without disturbing landscaping or property lines.
When Interior Solutions Shine
For many NYC homes, limited setbacks and shared walls make exterior work impractical. An interior perimeter drain tied to a sealed, battery-backed sump paired with a dimple mat and vapor barrier under new flooring reliably controls water. Add backwater valves on sewer lines and check valves on discharge to prevent re-entry.
Hybrid Approach for Peace of Mind
Combine exterior grading/downspout extensions (move roof water 6–10 feet away) with interior drainage, foam-insulated walls (to warm surfaces), and continuous slab vapor control. Elevate critical equipment and use moisture-smart finishes (porcelain tile, SPC LVP) so occasional wetting doesn’t become a disaster.
Testing & Monitoring
Perform moisture mapping before design, photograph weep points, and plan accessible cleanouts. Add leak sensors and humidity monitors, and plumb the dehumidifier to a dedicated drain.
See step-by-step assemblies and details in our NYC basement waterproofing and moisture control.