Basement waterproofing companies in Long Island

An independent, hand-verified directory of companies that install basement waterproofing systems in Long Island, New York: from Nassau County in the west, through Suffolk County, to Riverhead, the North Fork, the Hamptons and Shelter Island in the east. Every fact below comes from the company's own website, as recorded in our research. Where a company publishes no address, no rating or no license number on its own site, we say so plainly instead of filling the gap from a directory.

Long Island rules: read this first

New York has no state basement-waterproofing license as such. What companies publish are county home-improvement contractor licenses: Nassau and Suffolk. That is why this guide shows a license number only where the company publishes one on its own website: only 4 of the 20 companies in this guide publish a license number on their own site. The rest either state only that they are licensed and insured, without a number, or publish no license mention at all. A directory award, a review-site badge and a mold-remediation license are not waterproofing licenses, and none is presented as one here. A website claim of being licensed and insured, without a number, is a claim, not a verified credential: ask the company for its license number and verify it yourself with the county.

This guide describes waterproofing only as water control, dryness and structural protection: keeping water out of the basement, keeping the space dry, and protecting foundations, walls and floors from water damage. It never presents waterproofing as a benefit to personal well-being.

What the research found

• 20 companies with their own websites, approved one by one.
• Only 4 of the 20 publish a license number on their own website: Healthy Basement Systems (Nassau HI 201334, Suffolk HI 71430), Long Island Foundation Co. (Suffolk HIC 61442-H confirmed, Nassau number in internal conflict), Home Healthy Homes (Nassau H3101780000, Suffolk 40674-H), and Suffolk County Waterproofing Contractors (a published license string quoted verbatim with reservation).
• Only 4 of the 20 publish a rating with a review count on their own website: ACM Basement Waterproofing (5 with 160 reviews), Healthy Basement Systems (4.9 with 30 reviews on area pages, with a 612-total-reviews figure noted), LI Basement Pro (4.9 with 187 reviews) and Long Island Foundation Co. (4.9 with 214 reviews). Every other profile shows no rating with a count. A cross-platform aggregate is not counted as a single rating with a count.
• 0 of the 20 publish a fixed waterproofing price on their own website. The only dollar figures found are ranges and discounts, quoted in the cost guide and labeled as such.
• Service-area companies serve Long Island but publish no street address on their own site. They are marked as such: 4 of the 20 (LI Basement Pro, Diamond Masonry & Waterproofing, E&M Waterproofing and Twin Fork Waterproofing).
• Shelter Island is expressly named by only 2 of the 20 on their own sites: ACM Basement Waterproofing and A.M. Shield Waterproofing. Most companies claim a county or Long Island in general without naming every town.
• Twin Fork Waterproofing is listed with a verified limitation: its own main page does not name interior drainage, French drain or sump pump systems by name, and no internal page of its own site naming them was found, so it is not presented here as an interior-drainage or sump-pump specialist, and Shelter Island is not claimed as its coverage from its own site.
• Some companies are ancillary, not pure waterproofing specialists: Advanced Home Improvements is a general remodeler with waterproofing as one of its lines; JT Masonry & Landscaping is primarily a masonry and landscaping company; HRC Waterproofing is based in Queens and names Suffolk only through Huntington; Foundation Crack Repair is a foundation-repair firm with waterproofing as one of its services; Complete Basement Systems is the residential brand of Premium Technical Services.
• Companies that could not be verified from their own websites were left out of this guide before review, including lead-generation style sites, testing-only firms, out-of-area firms and firms with no verifiable own site; no company was excluded during the one-by-one review, and all 20 presented companies were approved.

All 20 companies

Built over a high water table

Much of Long Island sits just above the water table, so heavy rain and coastal storms push groundwater against basement walls and floors. An interior drainage channel collects that water where it enters and routes it to a sump pump, keeping the floor dry.