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/// Service

Foundation Waterproofing

Water is the root cause behind most foundation failures on Long Island. The island's high seasonal water table, coastal storm surge exposure, and poorly draining clay pockets drive hydrostatic pressure against basement walls and floor slabs across Nassau and Suffolk counties. Signs you need waterproofing include recurring dampness or puddles after rain, white mineral deposits on walls, musty odor, and visible mold growth. We design each system to the actual water source and volume — interior perimeter French drains tied to battery-backed twin sump pumps for hydrostatic issues, exterior dimple membrane with drain tile where surface runoff is the driver, and vapor barriers with dehumidifiers for residual moisture control. Most interior systems install in two to three days, with costs typically ranging from $4,500 to $15,000 depending on basement perimeter length.

Book Free Assessment (516) 529-6996
/// What's included

Engineered. Documented. Warrantied.

  • 01Hydrostatic pressure analysis to size the system correctly
  • 02Interior perimeter French drain tied to twin-pump sump system
  • 03Exterior dimple membrane and drain tile where conditions require
  • 04Vapor barriers and dehumidifiers to control residual moisture
  • 05Written no-seepage warranty backed by a real company that answers the phone
Foundation Waterproofing
/// Typical investment
$4,500 – $15,000 typical
Exact number after on-site assessment.
/// Process

4 Steps. No Theatre.

01

Diagnose

Water intrusion source identified — hydrostatic, surface runoff, or seasonal water table.

02

Design

System sized to the actual water volume. Not a template kit.

03

Install

Interior French drain, drainage matting, sump pits, battery-backed twin pumps, vapor barrier.

04

Warranty

Tested with a garden hose simulating storm load. Written warranty stays with the home.

/// Questions

FAQ.

01Why not just seal the outside?+
Exterior sealing works for new construction. On existing homes it requires full excavation, costs 3× more, and often doesn't outperform interior systems. We use exterior only when conditions demand it.
02What if my sump pump fails?+
We install twin pumps (primary + battery backup) so a single-pump failure never causes flooding. We also offer annual maintenance visits.
03How much does basement waterproofing cost in Nassau County?+
Interior French drain systems with sump pump installation for a typical Nassau County basement (1,000–1,500 sq ft perimeter) run $6,000–$12,000. Exterior waterproofing with dimple membrane and drain tile costs $15,000–$30,000 and is only necessary when surface runoff is the primary driver. Battery-backup sump pump additions run $800–$1,500. We provide a written fixed-price quote after the free on-site assessment — cost is determined by perimeter length, water volume, and whether dual pumps are needed given Nassau's storm surge exposure.
04Do I need a permit for foundation waterproofing on Long Island?+
Interior French drain systems and sump pump installations typically do not require a permit in Nassau or Suffolk County. Exterior waterproofing that involves excavation deeper than 4 feet may require a permit from the relevant Town building department — Town of Hempstead, Town of Oyster Bay, or the applicable Suffolk Town. We identify permit requirements at the assessment and handle any filings required.
05What causes water intrusion in Long Island basements?+
Long Island has three primary water intrusion drivers: (1) Hydrostatic pressure from the seasonal water table, which sits within 4–8 feet of grade across much of Nassau's south shore and can push directly through block and concrete foundations; (2) Clay soil pockets in Nassau's glacial till that hold water against the foundation wall after rain events; (3) Inadequate grading and downspout discharge that pools surface water against the foundation. Identifying the actual driver matters — a French drain solves hydrostatic pressure, but if your downspouts are discharging against the wall, we fix that first.
06How long does a basement waterproofing warranty last on Long Island?+
Our interior perimeter French drain systems carry a written no-seepage warranty that transfers with the property at no cost. Battery-backed sump pumps carry a manufacturer warranty (3–5 years on the pump, lifetime on the basin). We also offer annual maintenance visits that keep the pump operational and the drainage channel clear. The warranty is backed by a licensed, insured company — not a warranty card that goes to a holding LLC.
/// Related Services

The Other Six Fixes.

01
Crack Repair
02
Wall Repair
03
Pier Systems
04
Carbon Fiber
05
Crawl Space
06
Settlement
/// Book

Free Assessment.
Engineered Report.

A LI Foundation Co. tech will be on-site within a week. Assessment is free, report is included, no pitch at the end.

(516) 529-6996
/// Request

Assessment Request

No sales pitch. No “today only” nonsense. We call back within 4 business hours. Prefer to talk? (516) 529-6996