Can dormer windows be custom-sized?

Yes. Dormer windows are often custom-sized to fit unique rooflines and angles for proper sealing and long-term performance.

Dormer Window Replacement in St. Louis

Upgrading your dormer windows can dramatically improve comfort, reduce drafts, and enhance your home’s energy efficiency. At STL Windows and Doors, we specialize in dormer window replacement for St. Louis homeowners with aging, leaking, or inefficient dormer windows.

Our expert installation process is designed for roofline applications and backed by a 10-year workmanship warranty.

Dormer window replacement involves removing failing or outdated windows and installing new, energy-efficient ones designed to withstand roofline exposure and St. Louis weather conditions.

Properly replaced windows help prevent leaks, improve airflow, and stabilize temperatures in upstairs rooms while boosting curb appeal and long-term home value.

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Dormer Window Replacement for St. Louis Homes

Dormer window replacement services are designed for homeowners with windows that no longer seal properly, operate smoothly, or meet modern energy-efficiency standards. At STL Windows and Doors, we replace dormer windows on one- and two-story homes using materials and installation methods suited for roofline exposure and Missouri’s seasonal extremes.

Our window replacement services include:

Removal of existing windows
Installation of energy-efficient replacement windows
Proper flashing, sealing, and waterproofing
Interior and exterior trim finishing
Cleanup and final quality inspection

This service is ideal for:

Homes with drafty or leaking windows
Finished attic or upper-level rooms with temperature issues
Older homes with original or builder-grade windows
Homeowners planning energy upgrades or exterior renovations

When You Need Dormer Window Replacement

Dormer window replacement is needed when existing windows fail to insulate properly, allow water intrusion, or no longer operate as intended. If you’re unsure whether it’s time to upgrade, review our guide, 10 Signs On When To Replace Windows In Your Home, to help identify common warning signs.

Because these windows sit directly along the roofline, they are more vulnerable to moisture, temperature changes, and structural movement than standard wall-mounted windows.

Common signs you may need window replacement include:

Noticeable drafts or heat loss in upstairs rooms
Condensation or fogging between window panes
Rotting, warping, or soft window frames

Leaks during heavy rain or freeze/thaw cycles
Ice buildup around windows in winter
Difficulty opening, closing, or locking windows

Why Factory Dormer Windows Fail

Factory-installed dormer windows often fail prematurely because they are not engineered for roofline exposure and extreme weather conditions. Many builder-grade windows lack proper insulation, sealing, and structural reinforcement, leading to air leaks, moisture intrusion, and accelerated wear in St. Louis’ climate.

Common causes of dormer window failure include:

Thin glass that allows heat transfer
Poor weatherstripping that leaks air
Seal failure during freeze/thaw cycles
Frames that warp in humid summers
Inadequate flashing for roofline applications

Dormer windows on a building in St. Louis showing slight damage.

Dormer Window Options at a Glance

Dormer window replacement offers several window style options, each suited to different rooflines, ventilation needs, and architectural designs. Choosing the right window type depends on dormer size, access, airflow requirements, and the overall look of the home rather than a one-size-fits-all solution.

Window Type	Best For	Airflow	Appearance	Pros	Cons
Casement Windows	Narrow or steep dormers	Excellent	Clean, modern	Tight seal, easy operation, strong ventilation	Crank hardware may limit screen options
Double-Hung Windows	Larger or traditional dormers	Good	Classic	Familiar look, flexible ventilation	Less airtight than casement styles
Slider Windows	Low-profile dormers	Moderate	Contemporary	Space-saving, easy maintenance	Limited airflow compared to casement
Fixed / Picture Windows	Light-only dormers	None	Open, unobstructed	Maximum natural light, no moving parts	No ventilation
Architectural / Specialty Windows	Custom dormer designs	Varies	Custom	Unique shapes, strong curb appeal	Requires custom sizing and planning

Our Top Dormer Window Replacement Recommendations

We recommend dormer window styles based on roof pitch, dormer size, ventilation needs, and architectural style. Our recommendations prioritize energy performance, durability, and ease of operation.

Casement Windows

Casement windows are one of the most popular choices we see homeowners choose for dormer applications because they provide excellent ventilation while sealing tightly against wind and rain. Since casement windows crank outward, they work especially well in narrow dormers or steep rooflines where traditional sliding or double-hung windows are harder to operate.

Their compression-style seal helps reduce drafts in upper rooms that are exposed to St. Louis winter winds and summer heat.

Double-Hung Windows

Double-hung windows are often selected when homeowners want to preserve a traditional architectural look, especially on colonial, craftsman, or historic homes. These windows allow ventilation from both the top and bottom sash, which can help manage heat buildup in upstairs spaces.

Double-hung windows are best suited when there is enough wall height to accommodate the full frame without compromising sightlines.

Slider Windows

Slider windows are a practical option for dormers with limited vertical space or modern exterior designs. Because they operate horizontally, slider windows are easy to open and maintain, even in tight attic or loft areas.

Homeowners often choose slider windows for dormers, prioritizing simplicity, durability, and minimal visual obstruction over maximum ventilation.

Architectural / Specialty Windows

Architectural and specialty windows are ideal for dormers with unique shapes, angles, or design goals. These custom windows are often used to enhance curb appeal, add natural light, or complement distinctive rooflines.

Because these windows are custom-sized and shaped, proper measurement, flashing, and installation are critical to prevent leaks and ensure long-term performance.

Dormer Types We Work With

At STL Windows and Doors, we replace windows in a wide range of dormer styles, including gabled, hipped, and flat-roof dormers. Each type presents unique structural, insulation, and waterproofing considerations, which is why proper window selection and installation methods are critical for long-term performance in St. Louis homes.

Gabled Dormers

Most common dormer type
Excellent ventilation potential
Compatible with casement or double-hung windows

Hipped Dormers

Strong weather resistance
Works well with casement or architectural windows

Flat-Roof Dormers

Require enhanced insulation and waterproofing
Best paired with high-performance glass
More prone to leaks if improperly installed

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Our Dormer Window Installation Process

Our window replacement process follows a structured workflow designed to protect your roofline, interior spaces, and long-term window performance. We begin with an inspection and assessment of your space and finish with a final inspection and meticulous cleanup.

Inspection & Assessment – Evaluate existing windows, framing, and roofline conditions
Window Selection – Match window type to dormer design and performance needs
Precision Measurements – Ensure proper fit and sealing
Roofline Integration – Coordinate flashing and structural support
Installation – Secure replacement windows with proper alignment
Sealing & Waterproofing – Prevent leaks and air infiltration
Final Inspection & Cleanup – Confirm quality and remove debris

Custom Dormer Window Options

Dormer windows often require custom sizing and design features to match rooflines and architectural details. We offer a wide range of customization options to ensure a perfect fit and finish.

Custom options include:

Custom window sizes and shapes
Frame colors and interior finishes
Low-E and insulated glass packages

Laminated or tempered safety glass
Energy Star–rated configurations
Decorative grid designs

Why St. Louis Homeowners Choose STL Windows and Doors

Aeris Bay Window Front of Home in St Louis

St. Louis homeowners choose STL Windows and Doors because we specialize in complex window installations and understand local weather demands. Our team delivers precision installation, clear communication, and lasting results.

What sets us apart:

Platinum ProVia Dealer & Certified Installer
In business since 2014
10-year workmanship warranty
Experience with all dormer styles
Licensed and insured professionals
Local St. Louis expertise
Hundreds of 5-star reviews

What Our Customers Say

Homeowners across the St. Louis area trust us for window replacement projects that require precision, durability, and roofline expertise.

“Every person we dealt with was absolutely professional and amazing to work with during a large, and sometimes challenging, job! Highly recommend them to anyone. Too bad more companies don’t have such dedicated, polite employees!”

– Valeria B.K.

“I have used Stl windows and doors for several projects and they have always done a great job. Everyone is very nice and professional and the work they do is awesome.”

– Alex S.

“STL Windows & Doors is an outstanding company! The sales manager Dan, made the process very easy and the window installation went great! The windows look beautiful and the installers, Jake and Duke, were friendly and very professional. When the job was complete and the work areas meticulously cleaned, other than the new windows, it didn’t even look like they were here…”

– JoAnne E.

      EXCELLENT  
   Based on 199 reviews 
    
 
 
 
   
 
 
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   Jeff Gordon 
 
 
 
 Trustindex verifies that the original source of the review is Google. Peyton and Max installed 21 new windows and a new front door. They were a pleasure to work with, especially since we had other home improvement projects going at the same time. They did meticulous work and answered all of our questions.
  
 
     Posted on Google  
   
   Mike Kelly 
 
 
 
 Trustindex verifies that the original source of the review is Google. I had a great experience with STL Windows and Doors. They we're booked up initially, but they still were able to setup an appointment and put me on the schedule.

This company has great prompt customer service, fair pricing, and great professionalism. I would highly recommend their service.
  
 
     Posted on Google  
   
   Anne Croy 
 
 
 
 Trustindex verifies that the original source of the review is Google. Excellent service with initial sale and installation!!  High quality product.
  
 
     Posted on Google  
   
   Vivian Saied 
 
 
 
 Trustindex verifies that the original source of the review is Google. I used Stl windows and doors to replace half of the windows in my house and a sliding door. The whole process was excellent. From talking with Dan, the sale manager to the installers (Tony and his crew ) to Scheduling with Chris at the office. First of all, Chris was able to up my schedule date a week early upon my request. I'm sure he squeezed me in his tight schedule. I was very thankful. Tony and his crew were very professional, yet  friendly and considerate. They were prompt on time the 3 days they came and very efficient. They took down my window treatments and put them back up again exactly the way they were. They moved furniture and put back.  They took the time to explain how the windows opened from top to bottom as the windows had many options that my old windows didn't have. I would use them again and would definitely recommend them to my family and friends
  
 
     Posted on Google  
   
   Elizabeth Purcell 
 
 
 
 Trustindex verifies that the original source of the review is Google. Worth the wait! Price was insanely different from other bids for a single window replacement. Paid cash for a slightly better rate. Originally was going to need to wait 8 months for replacement but I got lucky & they fit me in at the 4 month marker since they had a cancellation.  Customer service from Kaleb & Tony was outstanding.  Both were very personable & made me feel confident that the job was being done well.  Great warranty! Glad to check this off my list:)
  
 
     Posted on Google  
   
   Aaron Fox 
 
 
 
 Trustindex verifies that the original source of the review is Google. STL Windows and Doors did an excellent job with our window replacement project. We live in an older home (over 100 years old) and we know there are going to be issues related to its age. The STL Windows and Doors team worked extremely hard with us to replace one of our bathroom windows that had begun to show signs of water damage. After the initial window replacement project was finished, we did communicate with their team about concerns we had with the original window frame that remained. Chelsea worked with us and a team (Tony and Caleb) came to our house within a week and replaced the frame as well. Their prices were reasonable and they had an array of choices. Overall, we highly recommend them for any window-related project you may have!
  
 
     Posted on Google  
   
   Jake Bloomer 
 
 
 
 Trustindex verifies that the original source of the review is Google. Experience was great, STL W+D replaced our old rear door and transom with a new eight-foot unit. It’s great to have this huge pane of glass looking out over the back yard. Installers were great and clean and shimmied the door in without removing our old casing and messing with the plaster. They know what they are doing!
  
 
     Posted on Google  
   
   Randall H 
 
 
 
 Trustindex verifies that the original source of the review is Google. The removal of the old window and the installation of the new window went more smoothly than I would have expected. Peyton and Max were knowledgeable, professional, and completed the installation beautifully and efficiently. Both of them did a great job with making in the new window secure, sealed, and attractive.
  
 
     Posted on Google  
   
   T Baker 
 
 
 
 Trustindex verifies that the original source of the review is Google. Premium products and service at a more affordable price. Fantastic experience at every step of the process. Had some hail and tornado damage. Jared (sales) was friendly and knowledgeable about the industry. Did not hard sell, but instead provided a balanced and very detailed explanation of STL's products and services vs competitors, which felt trustworthy. Dan (owner) came out to measure the windows. My spouse said he was friendly and answered her questions. We got an unexpected scheduling break and installed much sooner than the expected wait. The installers, Peyton and Max, were friendly, efficient, and conscientious of our home. Their finish work (sealing and caulking) is better than the original for the house. They took the time to demonstrate all the features of the new windows and how to care for them. We all noticed a defect in the glazing inside one of the window sashes, which they immediately reported to the owner who, in turn, called me immediately about the manufacturer's quick replacement. Provia warrantees the vinyl, glass, hardware and screen of the window for life and this guarantee is transferable once to a new home owner. The installation has a 10-year guarantee. Also, STL has another business for window cleaning and screen replacement, which we're going to check out.
  
 
     Posted on Google  
   
   Jessica Klemp 
 
 
 
 Trustindex verifies that the original source of the review is Google. Great company to work with! We needed four hopper windows replaced on our garage/basement and STL Windows and Doors provided the best service and most competitive pricing. The work was done quickly and professionally, and everyone we met from the company was friendly. We would recommend calling them for your window needs!

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Service Areas We Cover

We provide window replacement services throughout the St. Louis metro area, including St. Louis City, St. Louis County, St. Charles County, and Jefferson County. Our team services residential neighborhoods across the region with local expertise and fast response times.

Frequently Asked Questions

Yes, replacing dormer windows can increase home value by improving curb appeal, energy efficiency, and comfort in upper-level living spaces. In St. Louis homes with finished attics or bonus rooms, updated windows are especially attractive to buyers and can positively influence resale value.

Dormer windows can be more prone to leaks than standard windows because they sit along the roofline and are exposed to more water and snow. When installed with proper flashing, waterproofing, and sealing, professionally replacedr windows are just as reliable as other windows.

Most dormer window replacement projects are completed within one day per window, depending on roof access, window size, and dormer design. Larger or custom windows may require additional time to ensure proper flashing, sealing, and roofline integration.

Yes ,they are often custom-sized to fit unique rooflines, angles, and openings. Custom sizing ensures proper insulation, weather sealing, and long-term performance, which is especially important for windows installed along sloped roofs.

Ready to Replace Your Dormer Windows?

If your windows are drafty, leaking, or outdated, professional replacement can restore comfort and efficiency to your home. STL Windows and Doors delivers expert dormer window replacement tailored to St. Louis homes.