Adding a Double Sink to Your Bathroom on Long Island

Converting from a single-sink vanity to a double sink is one of the most requested upgrades in Long Island master bathroom remodels. It's also one of the most misunderstood in terms of what it actually involves. This isn't just swapping a vanity — it often requires plumbing modifications and careful space planning to do correctly in older Long Island homes.

What's Involved in Adding a Second Sink

Adding a second sink to a bathroom that currently has one requires two things: space and plumbing. Both are straightforward in a new-construction layout. In older Long Island homes — which make up most of the housing stock in Nassau and Suffolk County — both can be more complex.

Space requirements: A proper double vanity needs a minimum of 60 inches wide to function comfortably — 30 inches per person. The existing bathroom wall needs that much clear space without obstruction from windows, doors, or protruding walls. Measure your current vanity wall carefully. Many older Long Island colonials and splits have 48–54 inch vanity walls, which is too narrow for a comfortable double sink without some reconfiguration.

Plumbing requirements: Adding a second sink means adding a second drain and a second set of supply lines (hot and cold). If the second sink is positioned near the first, this is straightforward — a plumber can tie into the existing drain and supply lines. If it's on the opposite wall or far from the existing plumbing, expect more involved work and cost.

In Long Island's older homes with cast iron drain lines, cutting into an existing drain stack to add a second connection can run $800–$2,000 just for the plumbing rough-in. Plan for this in your budget.

Double Vanity Options for Long Island Bathrooms

Freestanding 60-inch double vanity: The most common choice. A standard 60-inch vanity with two undermount sinks, quartz top, and soft-close drawers runs $1,200–$3,500 for the unit, plus $600–$1,200 for installation and plumbing connections. The plumbing for both sinks can usually run to a single shared drain stub-out if the vanity is replacing an existing single-sink unit.

72-inch double vanity: For larger master baths. More counter space per person, typically 36 inches each. Very popular in Long Island homes in the $800K+ range where master baths are larger. Cost: $1,800–$5,000 for the unit.

Custom or semi-custom: Some Long Island master baths have non-standard widths or specific design requirements that standard vanities don't address. Semi-custom vanities (standard cabinet boxes with custom finish and dimensions) provide more flexibility. Expect $3,000–$8,000+ for semi-custom work.

Vessel sinks: Vessel sinks (sinks that sit on top of the counter rather than under it) are a design statement that works well in master baths where you want a bold focal point. Cost of vessel sinks is comparable to undermount sinks, but the countertop requires different cutouts and the faucets need to be taller to reach over the vessel rim.

At Alec's Construction, we handle the full scope of double vanity installations across Long Island — design consultation, plumbing rough-in, vanity installation, countertop fabrication, and all required permits in Nassau and Suffolk County.