Planning a dormer

Shed or gable

1. 1A shed dormerOne wide box with a shallow roof across much of the roof's length. It adds the most standing room and floor area.
2. 2A gable dormerA smaller peaked dormer, often in pairs. It adds light and headroom in one spot and keeps more of the house's original look.
3. 3A full or partial dormerRunning the length of the house or only part of it. More length means more room, and more roof to rebuild.

What an attic needs to become bedrooms

• A real stair, not a pull-down ladder, landing where it does not cut a room on the floor below in half.
• An emergency escape opening in each sleeping room; your building department confirms the size the code asks for.
• Enough ceiling height once insulation and drywall go in.
• Heat and cooling that reach up there, and insulation in the new roof.

Framing, zoning and permits

Cutting into a roof changes how it carries weight, so a licensed engineer or architect designs the new framing. Towns treat a dormer as permit work: the Town of Babylon, for example, lists dormers among the projects that need a building permit, and a dormer can count toward height or floor area rules in the zoning code. Check your town or village through our permit guides.

What drives the cost

• The dormer's length, and whether it is a shed or gables.
• Engineering and any reinforcing of the existing floor below.
• A new stair, and what it displaces downstairs.
• A bathroom upstairs, which means plumbing through the house.
• Windows, insulation and finishes.

Before you sign with anyone

• Check the contractor's county home improvement license yourself: Suffolk or Nassau, plus any town license on the East End.
• Ask for a certificate of insurance sent to you by the insurance agent, not a photo of one.
• Get the contract in writing and signed. New York's home improvement contract law, General Business Law section 771, requires the contractor's license number, a description of the work and materials, the price, the approximate start and completion dates, and a schedule if there are progress payments.
• Know your two protections under that law: you can cancel until midnight of the third business day after you sign, and payments made before the work is finished must be deposited as the state's Lien Law requires, unless the contractor gives you a bond or similar guarantee instead.
• Match each payment to finished work. A payment schedule that runs ahead of the work leaves you carrying the risk.