Long Island's Basement Experts Since 2011
Basement Finishing Long Island
Long Island's most experienced basement contractor. 580+ basements completed across Nassau and Suffolk Counties since 2011. We've seen every quirk this soil has.
Mon–Sat, 7am–5pm · Free Estimate · No Obligation
Free Estimate — No Obligation
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Responds within a few hours · Mon–Sat 7am–5pm
Everything Your Basement Needs
Our Basement Services
From raw concrete to fully finished living space — we handle every phase in-house with our 14-person crew.
Basement Finishing
Transform your raw concrete basement into livable space. LVP flooring, drywall, recessed lighting, drop ceilings.
Basement Waterproofing
Interior drainage systems, sump pumps, and crack injection for Long Island's high water table and clay soil.
Water Damage Response
Emergency flood response — pump-out, drying, mold prevention, and full remediation. Fast response times.
Sump Pump Installation
Single and dual sump pump systems with battery backup. BSI-certified installation and maintenance.
Egress Windows
Code-compliant egress window installation for legal basement bedrooms. Includes excavation and window well.
Basement Renovation
Update an existing finished basement — new flooring, fresh drywall, updated lighting, ceiling replacement.
About LI Basement Pro
Built by a Long Islander, for Long Islanders
Dan Farrelly grew up in Hicksville and spent a decade as a finish carpenter before launching LI Basement Pro in 2011. He saw how many contractors were cutting corners on Long Island — skipping egress requirements, ignoring moisture issues, and leaving homeowners with code violations and water problems a year later.
We've done 580 basements on Long Island. We've seen every quirk this soil has. That means we catch the drainage problems before we frame. We spec the right LVP flooring for Long Island's temperature swings. We pull every permit so your finished basement adds real value when you sell.
Our team includes Karen Farrelly (office manager and permit coordinator), Mike Costello (BSI-certified waterproofing tech), and Tony Guerrero (15-year finish carpenter). We're not a referral network — everyone on your job works for us. Recent highlights include an exterior waterproofing membrane project in Nissequogue on a 1972 estate home near the Nissequogue River estuary, an exterior waterproofing membrane installation in Smithtown on Landing Ave, and a full basement finishing job in Kings Park.
Dan Farrelly
Owner · Hicksville native · 15 years
Verified Local Work
Recent Basement Jobs Across Long Island
Real jobs completed by our crew across Nassau and Suffolk Counties.
Full perimeter exterior waterproofing membrane on 1972 colonial estate — 180 linear feet, rubberized membrane with drainage board and footing drain
650 sq ft basement with LVP flooring, recessed lighting, and egress window
Interior drainage system + dual sump pump installation on cape-style home
800 sq ft basement with home office, bathroom rough-in, and drop ceiling
Two egress windows with full excavation and waterproofed window wells
Battery backup sump pump system after basement flooding
550 sq ft playroom/guest suite conversion with full drywall and LVP
Exterior waterproofing membrane + interior french drain system
Project Gallery
Before & After Basement Work
Real projects from Nassau and Suffolk County homeowners who trusted us with their basement.
Before: Raw Concrete Basement
After: Family Room
Before: Chronic Water Problem
After: Kids Playroom
Before: Unused Storage
After: Home Office
Waterproofing: Interior Drain System
After: Guest Bedroom with Egress
What Long Islanders Say
4.9 Stars · 187 Google Reviews
“Dan and his crew transformed our Hicksville basement into a beautiful living space. Professional, on time, and the quality is outstanding.”
Michael T.
Hicksville · Basement Finishing
“We had chronic water issues in our Levittown basement for years. Mike Costello installed a full drainage system and it's been bone dry through two major storms.”
Jennifer L.
Levittown · Waterproofing
“Got three quotes for our Commack basement. LI Basement Pro was the only contractor who measured properly and explained the egress code requirements.”
Robert M.
Commack · Basement Finishing
“Karen in the office was incredibly helpful coordinating Nassau County permits. The whole process was smooth and our finished basement looks incredible.”
Sarah K.
Garden City · Basement Finishing
“Emergency flooding in our Hauppauge basement. They were there within hours. Pump-out, drying, and remediation handled professionally. No mold issues.”
David R.
Hauppauge · Water Damage
Where We Work
Serving Nassau & Suffolk Counties
Nassau County
Suffolk County
Exterior Waterproofing
Basement waterproofing in NissequogueHigh water table · FEMA AE flood zone · Exterior membrane specialists · Estate homes
Waterproofing Expertise
Basement Waterproofing Across Long Island
Long Island sits on glacial till soil with a water table that can be as shallow as 2 to 6 feet below grade in coastal and low-lying areas. This creates hydrostatic pressure that pushes water through aging foundation walls — especially the concrete block foundations common in homes built from the 1950s through the 1980s. Our BSI-certified waterproofing technician Mike Costello has diagnosed and resolved water problems in hundreds of Long Island basements.
We offer both interior drainage systems for standard water management and full exterior waterproofing membrane installation for homes with severe hydrostatic pressure — particularly along the North Shore where water tables are highest. Our recent exterior waterproofing membrane work in Nissequogue village, where FEMA AE flood zones and glacial till soils create extreme groundwater conditions, demonstrates the depth of our capabilities.
Whether your basement needs a simple crack injection, an interior drain tile system with battery backup sump pump, or a full exterior waterproofing membrane applied to the foundation wall, we assess the specific conditions at your property and recommend the right solution — not the most expensive one. Read our waterproofing cost guide for detailed Long Island pricing, our exterior foundation waterproofing guide for membrane systems, or our basement water removal guide if you have standing water right now.
Interior Drainage Systems
Perimeter drain tile + sump pump. Best for most Long Island homes. $4,000 to $12,000.
Exterior Waterproofing Membrane
Full excavation, rubberized membrane, drain board, and footing drain. $8,000 to $25,000. See our Nissequogue work
Sump Pump + Battery Backup
TripleSafe and equivalent systems with automatic battery backup for storm protection. $800 to $3,500.
Crack Injection
Polyurethane or epoxy injection for isolated foundation wall cracks. $500 to $1,500 per crack.
Bay Shore · Islip Town
Basement Waterproofing Bay Shore NY
Bay Shore sits along the Great South Bay in the Town of Islip, and its combination of high groundwater, clay-heavy soil, and Superstorm Sandy flood history makes it one of the most challenging waterproofing environments on Long Island. Many Bay Shore homes — particularly those built in the 1960s and 1970s on Great East Neck Road, Pine Avenue, and the Brightwaters area — have concrete block foundations that are particularly vulnerable to hydrostatic pressure and efflorescence. LI Basement Pro has completed waterproofing projects throughout Bay Shore and the surrounding Islip Town communities, including Babylon and Islip.
For most Bay Shore homes, an interior drain tile system with a high-capacity sump pump and battery backup is the right solution — it manages the hydrostatic pressure without full exterior excavation. Typical cost for a Bay Shore interior waterproofing installation runs $4,500–$10,000 depending on linear footage and sump pit count. Homes in the FEMA AE flood zone (south of Montauk Highway toward the bay) may require larger pump capacity or a TripleSafe-equivalent dual-pump setup. The Town of Islip Building Department (655 Main Street, Islip) oversees permits for waterproofing work that involves structural changes; standard interior drainage systems typically do not require a permit.
We serve all of Bay Shore, as well as Brentwood, Islip, East Islip, Babylon, and West Babylon. Free estimates available on weekdays and Saturdays. Call (631) 625-8649 or submit a request below.
Got Questions?
Basement Finishing FAQs — Long Island
Every basement is different — size, moisture conditions, ceiling height, finish level, and permit requirements all affect the final number. We give free on-site estimates so you get an accurate quote specific to your home. Call us or request an estimate online and we'll visit within the week.
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Ready to Transform Your Long Island Basement?
Join 580+ Long Island homeowners who chose LI Basement Pro. Free estimates, no pressure, no obligation.
Mon–Sat, 7am–5pm · Free Estimates · No Obligation · Licensed & Insured