Onward
Quick answer: A dormer is a small roofed structure that projects out from a sloped roof, usually framing a vertical window. It’s a roof feature, not a whole-roof shape. Dormers add headroom, daylight, and living space to attics. Adding one costs about $2,500–$25,000 ($65–$300/sq ft) in 2026, and the flashing where it meets the roof is the main leak risk.
What a dormer actually is
A dormer is a structure that pushes out from the slope of a roof, with its own little roof and walls, usually built around a window. You’ve seen hundreds of them: those box-like projections breaking up the front of a Cape Cod, a Colonial, or a Craftsman. The window sits vertically, facing out, instead of lying flat in the roof like a skylight.
Here’s the important distinction. A dormer is not a roof shape the way a gable or hip roof is. It’s a feature added to a roof that already has a shape. The main roof might be a gable or a hip; the dormer rides on top of it. So when someone says “dormer roof,” they usually mean a roof that has one or more dormers, not a unique roofline of its own.
Every dormer has three basic parts: two cheek walls on the sides, a front face with the window, and its own small roof that ties back into the main roof. That tie-in is where most of the engineering — and most of the trouble — happens.
Why people add a dormer
Dormers solve a specific problem: the space directly under a sloped roof is tall in the middle and useless near the edges. A dormer carves out a pocket of full-height space and drops a window into it.
That gives you four things at once:
- Headroom. It turns a crouch-only attic corner into a spot you can stand in.
- Daylight. A vertical window pulls in more usable light and view than a flush skylight.
- Living space. Combined, those two make an attic into a real bedroom, office, or playroom.
- Curb appeal. A row of dormers breaks up a blank roof and adds the kind of architectural detail buyers notice.
It’s also a cheaper path than building out or up. A small gable dormer starts around $2,500–$8,000, while a full second-story addition runs into the tens of thousands. If your attic already has the framing and the slope, a dormer is the high-value move.
The main types of dormers
There are five dormer types you’ll meet most often. They differ in roof shape, how much space they add, and how much they cost to build.
Gable (doghouse) dormer
The most common type in the U.S. A gable dormer has a small peaked roof — two slopes meeting at a ridge — and a triangular front face above the window. It works with almost every house style, ventilates well, and is the simplest to frame. Per This Old House and HomeGuide 2026 data, small gable dormers run about $2,500–$8,000 each. Good for light and style; modest on floor space.
Shed dormer
A shed dormer has one flat roof that slopes gently in a single direction, with a flat front. Because it can span a long stretch of roof, it adds the most usable headroom and square footage — which is why it’s the workhorse of attic conversions. Cost is roughly $75–$120 per square foot installed, and a large shed dormer spanning the roof can total $15,000–$25,000.
Hip dormer
A hip dormer is like a gable dormer, but the roof slopes on three sides instead of two, giving it a small pyramid shape. It blends cleanly into hip-roofed homes and handles wind well, but the extra framing pushes cost to about $110–$140 per square foot. It adds a little less interior space than a gable of the same width.
Eyebrow dormer
An eyebrow dormer (or roof eyebrow) has a low, curved roof that ripples up over the window in a smooth wave, with no cheek walls. It’s almost pure curb appeal — it blends into the roof and adds the least light and space of any type. The curved framing makes it the most expensive at about $100–$160 per square foot.
Wall dormer
A wall dormer rises flush with the home’s exterior wall rather than starting partway up the roof slope. The front face lines up with the wall below, and the main roof tucks in on each side. It’s effectively a type of shed dormer and runs about $75–$115 per square foot.
How a dormer affects cost and complexity
A dormer always costs more per square foot than plain roof area, because it’s a small, detail-heavy build: cut framing, new valleys, flashing, siding, trim, and a window — all packed into a few feet.
Three things drive the number:
- Type and roof shape. Flat-roofed shed and wall dormers are cheapest; curved eyebrow and three-sided hip dormers cost the most.
- Size. A single-window dormer is far cheaper than a shed dormer running most of the roof’s length.
- What’s behind the wall. Attic conversions add insulation, electrical, egress, and interior finishing on top of the dormer shell.
As of 2026, the national average to add one dormer lands near $24,000 (Angi), but the range is wide — $2,500 for a small decorative gable to $25,000+ for a full-span shed. Onward can match you with vetted roofers who’ll quote your specific dormer rather than a national average. For broader roof pricing, see our roofing cost guide.
Waterproofing: the dormer’s weak point
This is the part that separates a dormer that lasts 30 years from one that leaks in three. Every dormer creates new intersections between roof planes, and every intersection is a potential leak point. Flashing failures at roof transitions — dormer cheek walls, the front apron, and the side valleys — are among the most common causes of water getting into a house.
Done right, the flashing layers like shingles do:
- Apron flashing protects the joint at the dormer’s front wall. Per Fine Homebuilding, the wall leg should be at least 6 inches tall (to tuck under the siding and water-resistive barrier) and lap over the roof shingles by at least 4 inches.
- Step flashing runs up each cheek wall, one piece per shingle course, woven into the siding.
- The cardinal rule: nail flashing through the roof leg into the deck, never through the siding or a vertical surface — driving a nail through the wall punctures its waterproofing.
Skip a step or stop the flashing short and you create a funnel that channels water straight inside. If you suspect a problem, our guide on how to find a roof leak walks you through tracing it. This is also why dormers are a job for an experienced roofer, not a weekend project.
When a dormer is the right call
A dormer makes sense when you have a steep enough roof, an unfinished or cramped attic, and a need for one more usable room. The classic trigger is an attic conversion — you want a third bedroom or a home office, the footprint can’t grow, and the attic has volume that’s wasted under the slope.
It’s the right call when:
- Your roof has real pitch (gable, hip, gambrel, or mansard). Low-slope and flat roofs don’t have the height to gain from a dormer.
- You need headroom and light, not just storage — a shed dormer for space, a gable or eyebrow for style.
- A full second-story addition is overkill or out of budget.
It’s the wrong call when the attic lacks structural capacity, when local code makes egress or ceiling height impractical, or when you only need storage (a skylight is cheaper). To see where dormered roofs fit among other rooflines, compare it with the standalone gable roof it usually sits on.
The bottom line
A dormer is one of the highest-value upgrades you can make to a sloped roof: it converts dead attic space into a real room, adds light and headroom, and lifts curb appeal — all for a fraction of a full addition. The catch is the flashing. A dormer is only as good as the waterproofing at its joints, so the contractor matters more than the dormer type you choose.
Thinking about adding a dormer or converting your attic? Get a free estimate and Onward will match you with vetted roofers who quote dormer work — flashing included — so you know the number and the plan before you commit.
