Frequently asked questions about basement waterproofing in Long Island
What is the difference between an interior system and an exterior system?
An interior system collects water inside the basement and channels it to a sump pump. An exterior system excavates outside the foundation and seals the wall with a membrane. Ask the company which option fits your foundation and your property, and what each one includes.
Why do some companies show no license number?
Because their own website publishes none, or states only that it is licensed and insured without a number. This guide shows a license number only where the company publishes one on its own website, and only 4 of the 20 companies here do. A directory award is not a license, and a mold-remediation license is not a waterproofing license. Ask the company for its license number and verify it yourself with the county.
Why do some companies show no rating?
Because their own website publishes no rating figure with a review count. This guide never invents a rating and never presents a review-site figure as if it came from the company's own site. No rating means no rating was found on the company's own site, not that the company is bad. Only 4 companies here publish a rating with a count.
Why do some companies show no street address?
Because their own website publishes none. This guide states that plainly instead of copying an address from a directory, which may be outdated or belong to a different business with a similar name.
Why is there no fixed price in this guide?
Because none of the 20 companies publishes a fixed waterproofing price on its own website. The only dollar figures found are ranges and discounts, quoted in the cost guide and labeled as such. A real price comes only after the basement is seen and a written quote is given.
Which companies serve Shelter Island?
Only 2 of the 20 expressly name Shelter Island on their own sites: ACM Basement Waterproofing and A.M. Shield Waterproofing. Other companies claim a county or Long Island in general without naming Shelter Island individually.
Why is Twin Fork Waterproofing listed with a limitation?
Because 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 in verification on 2026-11-03. It is therefore listed only as a general waterproofing and foundation-repair company for the East End, without interior-drainage or sump-pump systems attributed to it and without Shelter Island claimed as its coverage from its own site.
Should I choose the cheapest quote?
Compare itemized quotes, not headline figures. Scope, system type, discharge, crew, warranty and restoration can all differ between quotes that look similar at first glance.
What is a service-area company?
A service-area company serves Long Island but publishes no street address on its own site. Those companies are marked as service-area companies in this guide.