Dormer Additions on Long Island: What They Cost and What to Expect

If your home has a finished attic or a steep roof with unused space underneath, a dormer addition is one of the most impactful projects you can do. It adds windows, light, headroom, and in many cases a full bedroom or living area without expanding the home's footprint. On Long Island, where lot sizes are limited and moving is expensive, that kind of square footage matters.

A dormer is a structural addition that breaks through the existing roof plane to create a vertical wall with windows. At its core, it converts attic space from unusable crawl space into livable square footage. The result is more headroom, more natural light, and the ability to put a bedroom, bathroom, home office, or playroom where there was nothing before.

The existing roof is cut open, new framing is built to create the dormer structure, the roofing is tied back together, windows go in, and the interior is finished. It is a real construction project that involves roofing, framing, siding, windows, insulation, drywall, and often electrical and HVAC work.

Shed dormer

A shed dormer has a single sloping roof and runs the full width or most of the width of the house. It adds the most usable square footage of any dormer type. Most Long Island homeowners who are adding a bedroom or a full livable floor choose shed dormers because the space gain is substantial. It changes the look of the house noticeably from the outside.

Gable dormer

A gable dormer has a peaked roof and adds a single window on one section of the attic. It looks more traditional and is a better fit when the goal is to add light and a little headroom rather than full livable space. Several gable dormers across a roofline can significantly improve the look of a Cape Cod style home.

Hip dormer

A hip dormer has a three-sided sloping roof. It is less common but works well on certain architectural styles. Like the gable dormer, it is primarily used for light and modest space gain rather than full room conversion.

Dormer additions in Nassau County typically range from $35,000 to $85,000 depending on the type, size, and scope of interior work. A modest gable dormer on the lower end. A full-width shed dormer with a new bedroom and bathroom on the higher end.

• Structural engineering drawings and permit filing
• Roof opening and new framing for the dormer structure
• Roofing work to tie the dormer into the existing roof
• Exterior siding or trim to match the house
• Window installation
• Insulation and air sealing
• Drywall and interior finish
• Electrical work for lighting and outlets
• HVAC extension if the space will be conditioned

If you need more bedrooms or living space and the alternative is moving, a dormer almost always wins on cost. The average home sale in Nassau County comes with significant transaction costs on both ends. Adding a bedroom via a dormer is typically far less expensive and keeps your family in the neighborhood.

A properly done dormer addition also adds meaningful resale value. Adding a legal bedroom in Nassau County increases the home's appraised value and makes it more competitive in a market where bedroom count drives pricing.

Titan Project Solutions handles dormer additions throughout Nassau County from permit to final inspection. We manage the structural engineering, roofing, framing, and interior finish as a single project. Free estimates, no pressure. Call or text (516) 557-4933 to talk through your attic and what is possible.