Roof dormers can improve architectural design of your home, add living space, and provide other benefits, but what are your options? How much does a roof dormer cost?
This guide covers major dormer types and how much they cost to build. Before we delve into various dormer types, let’s quickly explore feasibility considerations and pros and cons of building a dormer:
Question: Is a roof dormer even feasible for your property?
Answer: It depends on the type of your roof frame; A stick-framed roof with an attic has room for adding a dormer, while a truss-framed roof doesn’t have any attic space to add a dormer to. You can still add a purely decorative make-believe dormer to a truss-framed roof, but not a real dormer.
There are several good reasons for a roof dormer:
Dormers add architectural interest, accent, and detail: Having one or more dormers as part of a roof’s structure can boost the curb appeal of a home that might otherwise be a bit bland. The new design features can look good inside too. You’ll enjoy the improved aesthetics of your home, and the upgrade will make it more appealing to buyers, if you decide to put it up for sale. Dormers have an average return on investment or recouped value of 65-70 percent.
Roof dormers add light: If the dormer is built above living space rather than over an attic, or if you’re converting attic space to living space, then it provides much-needed natural light. Dormers are wonderful spots for a reading nook, kids play area, dressing area and other uses where extra light is a bonus.
Improved ventilation: Dormers are built in multi-story homes on upper floors where heat rises and air can become stale and stuffy. The dormer window allows for fresh air and better airflow to improve the ventilation and air quality.
More room and headspace: When dormers are large, such as a shed dormer that runs the length of a bungalow, a 1.5-story home, the increase in usable space can make a difference.
A room with a view: In addition to light, the dormer provides another view on the world outside.
Another potential exit: In emergencies, a dormer window provides an exit opportunity. This is especially important if the dormer window is the only exit in an attic roof. If you have a multistory home, a rope or chain ladder should be kept in a handy upstairs location.
What should you be aware of before committing to a dormer?
Extra cost: Dormers require additional building materials and time — the inputs that increase the cost of construction. Getting the permit and hiring an architect, if necessary, boost costs not associated with simply tearing off shingles and installing a new set.
The cost will be slightly higher every time the home is reroofed due to additional materials and time requirements.
In 20-30 years, the window within the dormer will have to be replaced, another significant cost.
The best time to limit the cost of a dormer is when the home is being built. In existing homes, it is most cost-effective to add a dormer when a roof is being replaced.
Valleys: Most dormers create valleys on either side, and valleys are notorious for leaks because a higher volume of water runs through them. However, valley flashing materials are designed to prevent leaks, and experienced roofing contractors successfully roof valleys every day.
On our scorecard, dormers are ahead 6 to 2, so we think they’re worth the cost and risk, especially if you would like to add some visual appeal or additional living space to your home.
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Ten Types of Dormers and Their Costs
Here are the most common types of dormer for you to compare along with construction costs for each. As you will see, several dormer styles go by more than one name.
The costs provided in this guide are for the construction of the dormer frame and include average material costs for siding, windows and roofing. Architectural and building permitting costs can further increase your overall costs.
Note: the steeper the roof, the less the roof of the gable will extend out from the roof and the lower the cost of materials will be.
Arched top or barrel roof dormer:
A rounded top is the hallmark of this dormer type that has some wall space on sides and front. An arched or barrel dormer adds a soft contrast to the sharp, straight lines of most sloped roofs. This dormer type is less commonly called a segmental roof dormer.
- Use notes: Arched/barrel dormers are usually for light and visual appeal rather than to produce more living space. Consequently, they tend to be smaller than some other styles.
- Cost notes: A rounded roof takes more time to construct than a flat or gable roof
- Arched roof dormer cost: $100-$150 per square foot or $4,000 to $6,000 total
- Average cost and size: $4,650 for dormer 5’ wide x 8’ deep
Like arched top dormers, the roof of the eyebrow dormer is rounded. The difference is that the rounded portion blends directly into the roof on either side.
There are no side walls, just a small front wall, so eyebrow dormers are quite flat. Windows in eyebrow roof dormers are typically small, so they offer less light and ventilation than other styles.
- Use notes: Eyebrow dormers are installed for light and visual appeal, not increased space.
- Cost notes: Rounded roofs are labor-intensive, so they cost more than flat
- Eyebrow roof dormer cost: $105-$160 per square foot or $2,940 to $4,480
- Average cost and size: $3,925 for dormer 7’ wide x 4’ deep
Flat roof dormer:
via Mann’s Roofing
The flat roof on these dormers gives them a boxy appearance that isn’t as attractive as other types. However, building costs for the simple style are lower and the shape maximizes space beneath the roof and allows for larger windows and their advantages.
Flat, shed and wall dormers are often quite large. A disadvantage is that flat roofs don’t shed rainwater and melting snow like sloped roofing, so leaks are more likely, but a high-quality flat roof membrane such as PVC can be used to mitigate the risks of leaks due to a shallow slope.
- Use notes: These dormers are installed to create more space beneath, so they are usually large.
- Cost notes: Flat roofs have less roofing material but more siding, so your cost will vary based on the price of the materials you choose. The larger a dormer is, the lower its cost per square foot will be.
- Flat roof dormer cost: $80-$125 per square foot or $17,900 to $28,000
- Average cost and size: $24,500 for dormer 16’ wide x 14’ deep
Shed roof dormer:
A shed roof differs from a flat roof dormer only in that the roof is sloped. It has no peak; no hip and it isn’t rounded. Again, while not especially interesting, it does reduce construction cost while increasing (though not maximizing, as does a true flat roof dormer) the space beneath.
- Use notes: These dormers are installed to create more space beneath, so they are usually large.
- Cost notes: Since these roofs slope, there is less siding required for the dormer than on a shed roof dormer, but more work and cutting to accommodate the slope change.
- Shed roof dormer cost: $75-$120 per square foot or $16,800 to $26,880
- Average cost and size: $23,300 for dormer 16’ wide x 14’ deep
Wall roof dormer:
via M&M Construction
This is type of flat roof or shed roof dormer. Its front wall doesn’t blend into the roof, as with most flat/shed dormers, but is an extension of the home’s exterior wall. The purpose of the wall dormer is what you’d expect – more square footage beneath.
- Use notes: These dormers create the most floor space beneath because they extend to the home’s exterior wall.
- Cost notes: These dormers use more siding because they integrate with the exterior wall, but construction and roofing costs are lower than for other types per square foot.
- Wall roof dormer cost: $72-$115 per square foot or $25,900 to $41,500
- Average cost and size: $35,600 for dormer 20’ wide x 18’ deep
Gabled & flared gable dormer:
The gable dormer is the most common type. It has a roof that forms a peak with a triangular gable of wall above the window beneath. A flared gable features a peak that extends a foot or more out from the front wall. Its advantage is providing shade to the dormer window, so flared gable dormers are more common on the south and west sides of homes in North America.
- Use notes: Some gable dormers are installed for light and architectural appeal, while others are built to significantly increase space. As a result, gable dormers vary in size more than most.
- Cost notes: The slope of the gable roof and material used is a prime factor in cost. Flare roofs contain more materials and are more complex, so take longer to build.
- Gable roof dormer cost: $110-$150 per square foot or $7,050 to $9,600
- Average cost and size: $7,385 for dormer 8’ wide x 8’ deep
Hipped roof dormer:
via Roof Finials
Rather than a two-sided gable, a roof dormer has sloped roof sheathing and roofing materials on all three sides. The point at which the three sloping sides join is over the center of the dormer rather than at its front, as with a gable dormer. Hipped dormers maintain consistency with hipped roofs and add visual contrast to gable roofs.
- Use notes: Like gable dormers, some are for show and light while larger dormers are designed with adding space in mind, too.
- Cost notes: Hip dormers have more roofing and less siding, so again, material costs for each will play a role in total cost.
- Hipped roof dormer cost: $115-$135 per square foot or $7,360 to $8,640
- Average cost and size: $7,150 for dormer 8’ wide x 8’ deep
Recessed or inset roof dormer:
Recessed dormers have side walls that are beneath the slope of the roof, in contrast to standard dormers with walls extending beyond and above the roof. To compensate, there is a section of flat roofing in front of the window. It will hold water, adding concerns about potential leaks. Most recessed dormers are gabled, but rounded dormers can be recessed too.
- Use notes: These dormers are installed for light and visual appeal, and most are quite small.
- Cost notes: Less material is used in the construction of recessed dormers than in other types.
- Recessed roof dormer cost: $70-$100 per square foot or $1,680 to $2,400
- Average cost and size: $2,200 for dormer 4’ wide x 6’ deep
False or blind dormer:
This dormer type can take any of the shapes above. It gets its name because the dormer doesn’t penetrate the roof deck or sheathing into the living space of the house, meaning the dormer is not accessible or functional. The sole advantage or benefit is adding visual appeal to the home’s exterior.
- Use notes: While installed for visual appeal, false dormers tend to be on the small side relative to functional ones.
- Cost notes: Since the roof sheathing isn’t cut and no window is added, blind dormers cost the least to build.
- False roof dormer cost: $65-$90 per square foot or $4,160 to $5,760
- Average cost and size: $5,300 for dormer 8’ wide x 8’ deep
Pedimented roof dormer:
While most dormers are built entirely into the roof structure, a pediment dormer extends away from the roof and must be supported from below, usually by pillars or posts. The dramatic style of a pediment dormer looks best with classical architecture styles but might look out of place if your home has a contemporary or modern design.
- Use notes: These dormers are installed for looks, light, space and sometimes to create covered space for a porch, patio, driveway or entryway beneath.
- Cost notes: Costs include pillars, architectural windows, finished undersides and often high-end materials, and costs reflect these upgrades.
- Pedimented roof dormer cost: $165-$300 per square foot or $16,500 to $30,000
- Average cost and size: $24,000 for dormer 10’ wide x 10’ deep
How to Choose the Right Dormer Style?
What is your purpose for adding a dormer? Here are your best options for each:
- Looks: All but flat/shed/wall
- Light: All but blind, and the larger the better
- Room: Any but blind and eyebrow will add space, but flat/shed/wall dormers maximize space beneath
Simply make sure that the type you select fits your home style and isn’t so large that it overwhelms the exterior.
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