Exterior foundation waterproofing

What the work involves

The crew excavates along the leaking walls, down to the footing. They clean the wall, repair cracks and failed mortar, then apply a waterproofing membrane or coating. A drainage board often goes over the membrane to protect it and let water drop straight down. At the bottom, a footing drain in clean stone carries water away to daylight, a dry well or a sump. Then the trench is backfilled, ideally with soil that drains well, and the surface is graded away from the house.

• Excavation to the footing
• Wall cleaning and crack repair
• Membrane or coating
• Drainage board
• Footing drain in stone
• Backfill and grading

When it is worth it

Exterior work makes sense when water is coming through the walls themselves, when the wall is deteriorating from constant moisture, when you want the basement fully finished without relying on a pump, or when a foundation is already being exposed for another reason, such as an addition. It is harder where driveways, patios, porches, mature trees or a neighbor's house sit close to the foundation.

Rock, roots and tight lots

Lots in southern Westchester can be tight, and ledge rock and large boulders turn up in many yards. Rock slows excavation and can raise the price. Mature trees near the foundation complicate digging and can be damaged if roots are cut. Ask the contractor how they will handle each of these, and who repairs walkways, plantings and lawn afterward.

Permits and utilities

Excavation next to a foundation often needs a permit, and the contractor should pull it. Before any digging, underground utilities must be marked. Ask the contractor to confirm they have called 811 to request utility markings before any digging starts.

Comparing exterior and interior bids

If you get bids for both approaches, compare what each one actually solves. Exterior work keeps the wall dry and protects finishes inside. Interior drainage accepts that water reaches the wall and manages it, usually for less money. Ask each contractor what happens in a storm like Ida, whether their system depends on a pump, and what the warranty covers.

Timing and weather

Exterior work goes best in dry weather, when trenches stay stable and membranes cure properly. Long rainy stretches can stall a job, and frozen ground in deep winter makes digging harder. If your basement is leaking now, ask whether a temporary measure, such as extending downspouts or adding a pump, makes sense until the main work can be scheduled.

Ask the contractor how they protect the open trench overnight, especially if children or pets use the yard, and how long the excavation will stay open before backfill.

Typical exterior waterproofing costs

Published national figures. Not quotes.

National figures, rounded, not quotes. Your price depends on wall depth and length, soil and rock, access, landscaping and permits.

Sources: This Old House, basement waterproofing; Fixr, French drain; Fixr, basement waterproofing