How Much Does It Cost to Add a Dormer?

What Is a Dormer?

Dormers are window structures added to roofs—typically a sloped roof—that project vertically beyond the roof to increase useable space, add natural light, and improve the architectural design of your home. The dormer starts from the top floor of the home and has its own roof and siding surrounding the window that matches your preexisting siding. Dormer windows come in various shapes and sizes to match your needs and style preferences.

Can I Add a Dormer?

Before adding a dormer to your roof, you may need to invest in some repairs. The area may require upgrades or replacements, particularly to ensure the new material you use for the dormer matches your existing roof. 

“Depending on a home’s existing roof, the actual roofing material will naturally fade to some degree over time from sun exposure,” says Ezra Laniado, Angi Expert Review Board member and Owner, Landmark Construction & Development Group, Inc. “Because of this fading process, you should compare the color of the new dormer against the existing roof. In some cases you might need to reroof the house while adding the dormer to get a seamless finish.”  

Valleys are another consideration, which dormers create on either side. Valleys are notorious for leaks because water tends to collect in these areas, often at high volumes, and can put stress on the roof. While there are materials that a pro can use to prevent leakage, you’ll want to take additional precautions to ensure your roof won’t be another contributor to potential leaks. Here, too, you need to evaluate the roof’s age. An older roof, even though not leaking currently, will become more leak-prone once you start fiddling with it and agitating the waterproofing membrane. 

How to Calculate Dormer Costs

To determine the cost of adding a dormer, you first need to choose the style of dormer you want to install, where you want it installed, and the size. The type of roof you have will also determine the cost. Additional cost factors include permits, materials and labor, and any interior work that needs completing, such as drywall and painting.

To calculate the cost of adding a dormer, first consider any work that needs to be done before construction, including applying for permits and determining if your roof requires repairs or renovations. Next, determine the cost of the materials and labor for the dormer of your choice. Finally, calculate the cost of interior work, such as drywall and painting, and any associated labor costs.

Average Cost to Add a Dormer by Roof Type

Below are the costs of various dormer types.

Shed Dormer Costs vs. Gable Dormers

Gable dormers are the most common type of dormer and are typically found on roofs that have a steep pitch and an angle. These dormers are an attractive and cost-effective add-on that can let more light into your home.

Shed dormers are a bigger investment with benefits like increased square footage. Some people find shed dormers are the best way to add headroom and space to smaller homes.

A combination of a shed and gable dormer is a Nantucket dormer. For this type of upgrade, roofing pros erect two gable dormers and connect them with a shed dormer.

Dormer Cost Factors

Several components factor into the overall cost of your dormer addition. Below, we’ll discuss all of those factors in more detail.  

Labor

You might feel tempted to DIY this project, but adding a dormer is best left to a pro. Roofing contractors vary in how they estimate the cost of labor. Typically, a professional roofing contractor will charge a flat rate—about 20% to 30% of the total project cost—or an average hourly rate of $35 to $55 per hour. 

Type of Roof

The type of roof you have will factor into the cost of your dormer. It generally costs less to install a dormer in a home with an attic because it serves as an extension of the space. Attic dormers cost between $75 and $120 per square foot.

Cape Cod houses and bungalows are popular home styles that people add dormers to. Gable dormers are typically added to these homes with sloped roofs and can cost between $110 to $150 per square foot.

Framing

Framing is essential for an addition like a dormer. The cost to frame a roof ranges from $6 to $9 per square foot. Adding a dormer will likely fall on the higher end of that range due to the complexity of the design. 

Custom vs. Prefab or Faux

Prefabricated dormers cost between $8,000 and $14,000, not including the cost of labor and installation. The price comes from their size—which tends to be larger—and the cost associated with building, transporting, and lifting them.

You can purchase faux or “fake” dormers at a home improvement store. It’s more wallet-friendly to go this route, but you won’t reap the ROI benefits or the increase in square footage. 

Prefab or faux dormers are more common with DIY projects. However, this is a challenging roof project, and you should only take it on if you’re an advanced-level DIYer. 

Window Glass

Besides adding extra space, dormers also offer more natural light and ventilation with a window install. On average, window dormers cost $4,000 and can range in price between $3,000 to $8,000. 

Eyebrow dormers and arched top dormers are typically installed to bring extra light into a room but don’t offer additional space, so the cost is on the lower end of the range, between $3,000 to $4,500.

Reinforcement

Adding a dormer to your home will put extra weight on the frame and foundation of your house. Your roof may require additional support to hold up the material; if so, it could cost an extra $1,000 to $10,000.

Engineering

Dormer installation is a big undertaking that requires careful consideration to maintain the sound structure of your home. It’s a good idea to consider hiring an architect to assist you through the process of planning and installation. Architects typically charge per project, and their fees fall between 5% to 20% of the total project cost. 

Permits

You will likely need planning permission or a permit for a dormer. Generally, a building permit for an addition like a dormer costs about $1,160, or between $390 and $1,930. The true price depends on local laws in your area. Check with your local planning authority, who can help answer permit questions directly.

Cladding

Dormer cladding can cost anywhere from about $2 to $15 per square foot. Prices vary based on local material and labor costs, so the actual price may be higher. Cost factors include:

• Type of cladding

• Material removal

• Size of coverage area

Additional Changes

Depending on your roof, you may need to add roof trusses to accommodate the dormer install. A roof truss is a premade frame that can reduce labor costs and simplify assembly. Roof truss installation can cost between $7,200 and $12,000.

Adding a dormer will also require interior finishing, especially if you’re opening up a room. You’ll need to factor in the cost of drywall and paint as well as the labor associated with it, if applicable. 

Roof Replacement

If you’re choosing between replacing your roof or adding a dormer, roof replacement is the less costly option. The national average cost of roof replacement is typically between $5,700 and $12,000, or between $3.50 and $5 per square foot.

DIY vs. Hiring a Construction Pro

If you think dormers are right for your home, it’s best to leave the job to a local roofing contractor. They can help get local permits, follow building codes, and address any structural concerns they may find with your home. 

It might seem expensive to hire a pro, but adding a dormer involves opening up your roof and putting more weight on your home’s framing and foundation. If you take a chance and DIY this job without the proper training and experience, you risk damaging the structural integrity of your house and may need expensive repairs as a result.

FAQs

Do dormers add value to a house?

Yes, dormers add value to a house. The ROI (return on investment) for adding a dormer is around 40%, but you might save money on electricity bills over the years because there will be more light coming into your home.

You can increase the value of your home with other remodeling projects like adding a deck, finishing your basement, and upgrading your kitchen.

How much square footage does a dormer add?

Typical dormers typically add about 250 square feet, but this can be higher if you’ve remodeled other parts of your home or built on an addition.

What are other benefits to adding a dormer?

In addition to extra space and natural light, dormers can increase your home's curb appeal. A dormer can provide additional ventilation for your home as well.