A dormer addition projects out from a sloped roof to add headroom, light, and usable floor space to an attic or top floor, often turning unusable space into a real room. In 2026, dormers cost $90 to $150 per square foot, or $3,000 to $25,000 for most projects, with a national average around $15,000 to $24,000. A simple shed dormer is the cheapest path to real square footage; decorative gable and eyebrow dormers cost more per foot.
This guide breaks down dormer cost by type, what drives the price, and how a dormer compares to a full second story. For a tailored number, use the second story calculator or the main home addition cost calculator.
How Much Does a Dormer Addition Cost?
The short answer is $3,000 to $25,000, averaging $15,000 to $24,000. Small window dormers start near $3,000; a full-width shed dormer that creates a real room runs $20,000 to $55,000 once interior finishing is included.
- Small window / decorative dormer: $3,000 to $6,500
- Medium dormer (60 to 100 sq ft): $8,000 to $20,000
- Full-width shed dormer / attic conversion: $20,000 to $55,000
Dormer Cost per Square Foot by Type
Dormer style is the biggest price driver. Simpler single-plane roofs cost less; complex curved or peaked rooflines cost more.
| Dormer Type | Per Sq Ft | Best For |
|---|---|---|
| Shed | $75 to $125 | Maximum usable space; attic conversions |
| Flat | $90 to $130 | Modern look, low-slope roofs |
| Prefab | $70 to $100 | Budget-conscious, standard sizes |
| Gable | $110 to $150 | Curb appeal, classic styling |
| Hip | $110 to $150 | Hipped roofs, balanced look |
| Eyebrow / pedimented | $105 to $300 | Decorative architectural accent |
A shed dormer gives you the most floor space and headroom per dollar because its single, slightly-sloped roof needs the least framing and flashing. Gable dormers cost more and add less space, but they break up a roofline beautifully.
Where the Money Goes
| Component | Typical Cost |
|---|---|
| Roof removal & opening | $5 to $10 / sq ft of roof |
| Framing | $2,000 to $5,000 |
| Roofing & flashing (the leak-critical part) | 20 to 30% of project |
| Window(s) | $2,400 to $6,600 |
| Interior finishing (drywall, electrical, flooring) | $3,000 to $12,000 |
| Foundation / structural reinforcement (if needed) | $4,000 to $12,000 |
| Permits | $300 to $1,500 |
Flashing is where dormers succeed or fail: roughly 90 percent of dormer leaks trace back to poor flashing, so this is not the line item to cut.
What Drives Dormer Cost
- Roof pitch: A 6/12 pitch or steeper allows a classic gable or hip dormer. Shallow roofs limit you to shed dormers and reduce usable headroom.
- Ceiling clearance: You want at least 7 feet of vertical clearance at the dormer back wall for a code-compliant habitable room.
- Shell vs. finished: Framing only is far cheaper than a finished room with drywall, electrical, and flooring.
- Structural needs: Some roofs need reinforcement to carry the dormer load, adding $4,000 to $12,000.
- Existing roof condition: Opening the roof can reveal water damage or the need for new insulation.
Dormer vs. Full Second Story
A dormer is the cost-effective middle ground between living with a cramped attic and committing to a full second story.
| Factor | Dormer | Full Second Story |
|---|---|---|
| Cost | $3,000 to $55,000 | $150,000 to $350,000+ |
| Space added | Headroom + 60 to 300 sq ft | 800 to 1,500+ sq ft |
| Structural work | Moderate | Extensive (foundation, framing) |
| Roof work | Cut and frame an opening | Complete roof redesign |
| Timeline | 2 to 4 months | 5 to 8 months |
| ROI | 65 to 75% | 50 to 70% |
Dormer ROI
Dormers return a strong 65 to 75 percent at resale. Spend $30,000 and you might see a $20,000 to $22,000 bump in home value, plus the light, ventilation, and curb appeal a well-designed dormer adds. Because a dormer reuses your existing footprint and foundation, it is usually cheaper per square foot than a ground-level addition.
Timeline
Most dormers take 2 to 4 months including design, permitting, framing, roofing, and interior finishing. Weather is a real factor because the roof is open during framing; a good contractor has weather-protection protocols.
How to Save on a Dormer Addition
- Choose a shed dormer for the most usable space at the lowest cost per foot.
- Group multiple small dormers on one side to share roofing and flashing labor.
- Confirm your roof pitch and headroom before designing, so you do not pay for an unusable result.
- Do not cut corners on flashing; a leak costs far more than the savings.
- Finish the interior in a second phase if cash flow is tight.
- Budget a 15 percent contingency for hidden roof or insulation issues.
Dormer Addition FAQ
How Much Does a Dormer Addition Cost?
Most dormers cost $3,000 to $25,000, or $90 to $150 per square foot, with a national average around $15,000 to $24,000. Full-width shed dormers for attic conversions can reach $55,000.
What Is the Cheapest Type of Dormer?
Prefab and shed dormers are the most economical, at $70 to $125 per square foot. Shed dormers also add the most usable floor space.
Does a Dormer Add Usable Square Footage?
Yes, especially shed dormers, which add headroom and floor space and can turn an unusable attic into a habitable room with at least 7 feet of clearance.
Do I Need a Permit for a Dormer?
Yes. Dormers require a building permit and, in many cases, structural review, since they alter the roof structure.
What Is the ROI on a Dormer?
Dormers return roughly 65 to 75 percent at resale, among the better returns for a roof-level project, because they reuse the existing foundation.
Ready to price it? Use the second story calculator, or compare a full build-up in our second story addition cost guide.
