Dormer Addition Cost & Types Explained

Quick answer: A dormer addition typically costs $10,000 to $40,000 for most types, though a large full-width shed dormer that converts an attic into living space can run $50,000–$150,000. A small gable dormer runs about $18,000–$28,000. Dormers are one of the most cost-effective ways to add headroom, light, and usable space to a top floor.

Dormer cost by type

• Small / single gable dormer: $10,000 – $28,000

• Gable dormer (per sq ft): $110 – $150 / sq ft

• Shed dormer (per sq ft): $100 – $250 / sq ft

• Full-width shed dormer (attic conversion): $50,000 – $150,000

• Hip / specialty dormer: up to $45,000+

Types of dormers and when to use each

• Shed dormer — a single flat-sloped roof; adds the most usable space and headroom, ideal for turning an attic into a bedroom or bath.

• Gable dormer — the classic peaked dormer; the most popular for adding light and curb appeal with a modest footprint.

• Hip dormer — three sloped sides; blends well with hip-roof homes for a refined look.

• Gambrel & saltbox dormers — match specific roof styles common on New England colonials and capes.

• Cantilever dormer — extends beyond the wall below for extra space where the layout allows.

Frequently asked questions

Does a dormer add usable square footage?

Yes — a full shed dormer can turn a cramped, low attic into a full bedroom, bathroom, or office by adding standing headroom across the floor.

Do I need a permit for a dormer in Massachusetts?

Yes, dormers require a building permit because they alter the roof structure. We handle permitting and inspections.

Which dormer adds the most space?

A full-width shed dormer adds the most floor area and headroom, which is why it’s the go-to for attic-to-living-space conversions.

Get a free dormer estimate

Kneeland Construction builds shed, gable, hip, gambrel, saltbox and cantilever dormers across Greater Boston and the South Shore. Call 781-393-9899 or request a free estimate.