7 Things You Should Consider Before Adding a Dormer

Marwa Hasan
Written by Marwa Hasan
Updated July 20, 2021
Dormer windows on green house
Miles Nelson / Shutterstock.com

Adding a dormer to your home can give it a whole new look, but there are a few things to keep in mind before starting the process

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If you’re looking for a relatively simple way to change the look of your home, you can’t go wrong with a dormer. Adding a dormer not only refreshes the look of your house from the outside, but also expands the indoor living space. A dormer allows you to utilize the attic space in a whole new way, whether it’s a cozy reading nook or making it comfortable enough to be a spare bedroom. 

But, there are some things to consider before you begin your dormer project.

1. The Existing Roof

You should consider the shape, style, and angle of the existing roof before deciding on a dormer for your home. The roof of your new dormer should match the existing roofing material to create a consistent look. In addition, you should install roofing underlayments on the roof of your dormer to guarantee it's well protected.  

The roof section around the dormer may also need some repairs, upgrades, or replacement to ensure the new material will match perfectly and looks its best. You also may want to clean up your roof before installing a dormer. This way, you will get the full benefits of your roof’s new addition.

2. The Size of The Dormer Addition

The dormer should fit the scale of the house with a sense of proportion to the current roof. Otherwise, a dormer may end up being a dominant feature that could actually reduce the value of your house. 

The planned function of the space will help to determine the size of the dormer. However, the dormer generally should be small enough to break up the roofline and fit the roof without looking out of place. A dormer creates more headspace in an attic with a low ceiling while the window brings light into the room, so a window seat or a writing desk would fit nicely in a typical dormer.

3. The Permits

Before adding a new dormer, you will likely need to obtain a permit. A dormer permit costs an average of $1,160, or between $390 and $1,930, depending on local laws and regulations. It’s wise to look into these costs before getting started.

4. The Cost of Adding a Dormer

If you're looking to install a new dormer to your existing roof, it typically costs between $2,500 to $20,000, or $115 per square foot, depending on the size of the dormer you want to install.

Many options make a significant difference to the total cost, including the material, the size of the window, and the siding option. The cost of adding a dormer is different from the cost of installing a new roof, so be sure to talk to a pro to get a more customized estimate.

5. The Style Of The Dormer

There are different styles of dormers you can add to a building. The shape and structure of your existing roof will determine the dormer style, as it should match your roof's structure, suit the aesthetics, and improve the curb appeal, which will in turn increase the overall value of your property. 

Here are the different dormer types to choose from:

  • Gable dormer: Two planes sloped in the opposite directions creating a triangle-shaped dormer

  • Hipped dormer: Three sloping planes which usually match the hipped roof of the house

  • Flat dormer: One single horizontal flat surface covering the three-walled dormer

  • Shed dormer: A single flat roof that is sloped in the same direction as the roof

  • Wall dormer: An extension of the wall above the eaves level of the roof

  • Eyebrow dormer: A small arched window that sticks out from the slope of the roof

6. Dormer Windows

If you’re looking for natural light and ventilation in your attic, dormer windows are a great choice. The dormer window can come in various sizes and styles, but it’s usually smaller than other windows you’d find in your home.

Installing the right kind of window can be energy-efficient and help reduce utility bills like heating and lighting, as a window regulates the amount of light and heat coming in through the dormer.

You should also consider how to maintain and clean the dormer windows, either from the inside or the outside, depending on how the dormers open.

7. Dormer Draining System

You should also consider installing the right gutter. Not having a gutter on your dormer may lead rain to drip off and cause seepage into the walls or damage to the roof. The way water drains from the dormer gutter makes a big difference as well. You shouldn't install an open-ended gutter that drains to the roof, as this may increase moisture levels and create mold over time.

The best practice is to install a downspout, which takes water from the dormer's gutter to the lower gutter. This will help eliminate damages to the roofing caused by the water running off. However, if you don’t like how it looks, putting a metal tray under your downspout will lead water to the lower gutter without running on the roof. The metal tray is a safer option, and, bonus points, it blends well into the roof, so it's aesthetically pleasing.

You should install roof flashing along the seams where the dormer's roof meets your home’s roof to prevent water from entering the attic space and provide extra protection to your attic.

It's a great idea to inspect your roof to ensure your current gutter can handle the increased water coming from the dormer.

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