The Great Flattening: How to Replace Your Bay Window with a Regular One

When a Bay Window No Longer Works for Your Home

Can you replace a bay window with a regular window? Yes — and it’s more common than you might think.

Here’s the short answer:

• Yes, it’s possible. A bay window can be converted to a flat (regular) window.
• It requires structural work. The existing opening needs to be modified, and load-bearing elements must be properly supported.
• Permits are typically required. Especially in Chicago and the surrounding suburbs.
• Professional installation is strongly recommended. Bay windows often play a structural role in the home’s framing.
• The result can look great. A flat window can modernize your home’s exterior and simplify long-term maintenance.

Bay windows are beautiful — there’s no question about that. They add character, bring in extra light, and create cozy interior nooks. But they’re also complex structures that protrude from the home’s exterior wall, which makes them more vulnerable to drafts, leaks, and insulation problems over time. For many Chicago-area homeowners dealing with cold spots near the window, persistent moisture issues, or simply a desire for a cleaner, more modern look, replacing a bay window with a regular flat window is a practical and smart upgrade.

This isn’t a small job, though. It involves more than swapping out glass. It means rethinking the framing, siding, and interior finish of that entire wall section.

I’m Steve Mlynek, CEO and founder of HomeBuild Windows, Doors & Siding, with over 20 years of experience helping Chicago-area homeowners navigate exactly this kind of question — including whether can you replace a bay window with a regular window is the right move for their specific home. In the sections below, I’ll walk you through everything you need to know to make a confident, informed decision.

Basic can you replace a bay window with a regular window glossary:

• average cost of bay window and installation
• bay windows replacement
• replace flat window with bay window

Can you replace a bay window with a regular window?

The short answer is a definitive yes. You can absolutely replace a bay window with a regular window. However, unlike a standard “pocket” replacement where a new window slides into an existing frame, this is a “full-frame” conversion.

Because a bay window projects outward from the home, it occupies a three-dimensional space. When we “flatten” that space, we aren’t just changing the glass; we are essentially rebuilding a portion of your exterior wall. This involves a professional structural assessment to ensure the weight of the roof or the floor above is properly supported once the protruding structure is removed.

The process typically involves:

1. Removing the entire bay unit, including the roof skirt (if applicable) and the baseboard/seatboard.
2. Re-framing the rough opening to create a flat, vertical plane that aligns with the rest of your home’s exterior wall.
3. Installing a new load-bearing header if the width of the new window configuration differs from the original structural support.
4. Closing the gaps in your exterior siding and interior drywall.

Structural Considerations When You Replace a Bay Window with a Regular Window

One of the most critical aspects of this conversion is understanding how your current bay window is supported. Many bay windows in the Chicagoland area are “cantilevered,” meaning they hang off the house without ground support, or they may be “walk-out” bays that extend all the way to the foundation.

If your bay window supports a portion of the roof or an upper story, removing it without proper temporary bracing could lead to structural sagging or even collapse. We often find that older bay windows use a system of cables or wooden brackets that must be carefully decommissioned. When we replace a flat window with a bay window, we add support; when we reverse the process, we must ensure the remaining wall is reinforced with proper jack studs and king studs to maintain the home’s integrity.

Permitting and Professional Installation Requirements

In suburbs like Arlington Heights, Barrington, and Des Plaines, building codes are strict regarding structural changes. Converting a bay window to a flat one almost always requires a building permit because you are altering the “envelope” of the building and modifying the framing.

At HomeBuild, we handle the complexities of local codes for you. As a licensed and insured contractor, we ensure every project is owner-supervised. This means we don’t just drop off a crew; we oversee the structural modifications and the weatherproofing to ensure your home remains safe and dry. Attempting this as a DIY project is highly risky, as improper flashing or framing can lead to catastrophic water damage inside your walls.

Advantages of Switching to a Flat Window Design

While bay windows offer charm, regular windows offer efficiency and simplicity. Many homeowners choose to “flatten” their windows to achieve a more modern, minimalist aesthetic that complements contemporary siding like James Hardie® fiber cement.

One of the primary drivers for this change is energy efficiency. Bay windows have more surface area exposed to the elements. In our harsh Midwest winters, the “seat” of a bay window is often a major source of heat loss. By switching to a flat window, you reduce the exterior surface area and can utilize high-performance triple-pane or Low-E glass that helps regulate indoor temperatures much more effectively.

Maintenance Benefits After You Replace a Bay Window with a Regular Window

Maintenance is where regular windows truly shine. Because they don’t protrude, they aren’t subject to the same level of “beating” from snow, ice, and rain.

• Simplified Sealing: Bay windows have multiple joints and a dedicated rooflet that require frequent sealant inspections. A regular window has a much simpler flashing system.
• Cleaning Access: Standard double-hung or casement windows are much easier to clean from the inside.
• Longevity: Without the structural stress of “hanging” off the house, the frames of regular windows often stay square and functional for longer.

For more details on choosing durable materials, check out our replacement window buying guide.

Impact on Interior Light and Thermal Comfort

A common concern is whether the room will feel darker. While you lose the side-angle views of a bay, you can often compensate by installing a larger picture window or a bank of three regular windows in the new flat opening. This can actually provide a cleaner, more unobstructed view of your backyard or street.

The biggest “pro” is the elimination of drafts. Many older bay windows in the Northwest Suburbs suffer from “convection currents”—where cold air hits the large glass surface, drops to the floor, and creates a chilly breeze across the room. A flat, well-insulated window wall eliminates this phenomenon.

Feature	Bay Window	Regular (Flat) Window
Energy Efficiency	Lower (more surface area)	Higher (better insulation)
Maintenance	High (roof, multiple seals)	Low (standard flashing)
Interior Space	Adds a nook/shelf	Reclaims floor space
Cost of Unit	Higher	Lower
Midwest Winter Performance	Prone to cold spots	Excellent thermal break

The Step-by-Step Conversion Process

When we arrive at your home in Lake Zurich or Schaumburg to perform a conversion, we follow a meticulous installation process to ensure the new window performs for decades.

1. Site Protection: We set up barriers to protect your landscaping and interior flooring.
2. Demolition: The old bay unit is carefully disassembled. We inspect the underlying “rough opening” for any signs of rot or insect damage that may have been hidden.
3. Framing: We build a new wall section within the old opening. This includes installing a new header and studs to create a perfectly square opening for the new flat window.
4. Window Installation: The new Pella® or Andersen® unit is leveled, shimmed, and fastened.
5. Insulation: We use high-quality expanding foam and fiberglass insulation to seal the gaps between the new frame and your home’s structure.

Preparing the Exterior for Siding and Trim

Once the window is in, we have to address the “hole” left in your exterior. Since the bay window was wider and deeper than the new flat wall, there will be an area of the home with no siding. We specialize in matching your existing exterior, whether it’s vinyl, brick, or James Hardie siding. We apply a professional moisture barrier and high-quality flashing to ensure that water is directed away from the window and the wall.

Finishing the Interior Space

Inside, the conversion usually leaves a gap where the bay window’s seat used to be. We bridge this gap with new subflooring and drywall. Our team ensures the new drywall is taped, sanded, and ready for paint, so it looks like the bay window was never there. We finish the look with custom interior trim and window sills that match the rest of your home’s woodwork. For more on glass options during this phase, see our guide on double-pane vs. triple-pane windows.

Frequently Asked Questions

Do I need a building permit to replace a bay window with a flat one?

Yes. In almost every Chicago suburb, altering the structural framing of a wall requires a permit. As your contractor, HomeBuild handles the permit application process to ensure everything is up to code.

How long does the window conversion process typically take?

While a standard window replacement might take a few hours, a bay-to-flat conversion is a 1-to-2-day project. This accounts for the demolition, structural framing, exterior siding work, and interior drywall finishing.

Will removing a bay window affect my home’s resale value?

It depends on the condition of the bay window. A leaky, drafty, or outdated bay window actually detracts from value. A modern, energy-efficient flat window with high-quality trim and siding can improve curb appeal and reassure buyers that the home’s envelope is in excellent condition.

Conclusion

So, can you replace a bay window with a regular window? Not only can you, but for many homeowners in the Chicago area, it is the best way to improve home comfort and reduce maintenance headaches. By flattening that protruding space, you gain a more efficient thermal barrier against our brutal winters and a sleek, modern look for your home’s exterior.

At HomeBuild Windows, Doors & Siding, we pride ourselves on being more than just installers; we are structural experts. As an Elite Platinum Pella® Certified Contractor and an Andersen Certified Contractor, we bring over 20 years of experience to every project. Whether you are in Naperville, Elgin, or right here in Chicago, our owner-supervised projects ensure that your window conversion is handled with the highest standards of craftsmanship.

Ready to say goodbye to drafts and hello to a modern new look? Schedule a free consultation for your bay window replacement today and let us help you transform your home.