Double Casement Window: A Seamless, No-Mullion Design for a Modern Home


A double casement window without a mullion is a popular choice for homeowners seeking a modern and seamless design. These windows provide an unobstructed view, allowing for maximum natural light and a sense of openness in any room. In this blog post, we will delve into the world of double casement windows without mullions, exploring their benefits, installation process, and maintenance tips.

The Beauty of No-Mullion Double Casement Windows

Double casement windows, also known as French casement windows, consist of two sashes that open outwards from the center. Typically, a mullion, or vertical bar, separates the two sashes. However, many homeowners prefer a no-mullion design for its sleek and modern appearance.

By eliminating the mullion, these windows create an unobstructed view and allow for maximum natural light to flood the room. This design is perfect for those who want to enjoy the outdoors from the comfort of their home, or for spaces that require ample sunlight, such as a sunroom or kitchen.

Benefits of Double Casement Windows without Mullions

Aside from their aesthetic appeal, double casement windows without mullions offer several practical benefits:

1. Ease of Cleaning: With no mullion to obstruct access, these windows are easier to clean, both inside and out. This makes maintenance a breeze, especially for those hard-to-reach upper-floor windows.

2. Improved Ventilation: The wide opening of double casement windows allows for excellent airflow, making them ideal for rooms that require good ventilation, such as kitchens and bathrooms.

3. Enhanced Security: Double casement windows often feature multi-point locking systems, providing an added layer of security to your home.

4. Energy Efficiency: These windows are known for their tight seal when closed, which helps to prevent drafts and improve energy efficiency.

Installation Process

The installation process for double casement windows without mullions is similar to that of standard casement windows. It is essential to work with a professional window installer to ensure proper measurements and installation. Here are the general steps involved in the process:

1. Measurements: The installer will take precise measurements of the window opening to ensure a perfect fit.

2. Window Selection: Choose the right double casement window without a mullion that matches your home's style and your personal preferences.

3. Preparation: The installer will remove the old window and prepare the opening for the new window, ensuring a clean and level surface.

4. Installation: The new double casement window will be installed, making sure it is properly aligned and securely fastened.

5. Finishing Touches: The installer will apply any necessary insulation, sealant, and trim to complete the installation process.

Maintenance Tips

To keep your double casement windows without mullions looking and functioning their best, follow these simple maintenance tips:

1. Regular Cleaning: Clean the glass and frames with a mild soap and water solution, using a soft cloth or sponge. Avoid harsh chemicals or abrasive materials that may damage the window's surface.

2. Lubrication: Lubricate the hinges and locks with a silicone-based lubricant to ensure smooth operation and prevent wear.

3. Inspection: Periodically inspect your windows for any signs of damage or wear, such as cracked glass, damaged seals, or loose hardware. Address any issues promptly to prevent further damage.

4. Weatherstripping: Check the weatherstripping around your windows for wear or damage, and replace it as needed to maintain your window's energy efficiency.

By following these maintenance tips, you can enjoy the beauty and functionality of your double casement windows without mullions for years to come.

Final Thoughts

Double casement windows without mullions offer a sleek, modern design that enhances the beauty of any home. Their seamless appearance, combined with their practical benefits, makes them an excellent choice for homeowners seeking a stylish and functional window option. With proper installation and maintenance, these windows can provide a stunning view and improved energy efficiency for your home.

Casement Window


Casement windows are the most common style of window. They feature hinged panels that swing open and closed. Casement windows are available in single panels or multiple panels. The direction a door swings, either to the right or the left, is called the handing. In addition to handing, window are identified as either inswing or outswing depending on whether they open into the house or towards the outside.


Our team of experts will work with you to develop a bespoke plan that fits your needs. We take a holistic approach to the planning process, combining our technical expertise with our knowledge of customer requirements and project constraints.


Freedom to dream "truly custom-made"

Doorwin provides one-stop solution for professional windows doors manufacturer and installation. We have been serving customers with our high quality and branded products in United States, Asia and worldwide.


This newly built private house is in Sydney, Australia. The area occupied by the fenestration system in our scheduled design drawings was up to more than 110 square meters. A wide range of design details made the perfect mix of modern aesthetics and traditional sophistication, the simulated vertical hung windows with tilt & turn opening systems in this home are absolutely breathtaking. SDLS (Simulated Divided Lites with Spacer Bar) brings some historical vintage feeling to the whole building without losing any energy saving performance. Long narrow fixed windows creating larger-than-life expenses, coupled with German high-end systems made this project stand out from the rest.

Simulated Hung Window with Tilt & Turn Openings

The client's idea was to maintain a certain vintage feel, and our aim was to meet the energy efficiency needs and standards of modern houses as much as possible while maintaining a retro design. Doorwin’s 61S simulated hung windows with tilt & turn openings is a respectful modernization of a classic architectural masterwork.

Why choose the tilt and turn opening method?

Because it generally has better air seals than sliding, single hung, or double hung window frames. Tilt and turn windows form a complete seal when fully closed, this means they are less prone to water leakage, and cold draughts and you’ll keep more of your heating indoors where it belongs. They can be opened in the upper tilt way to ventilate at a minimum opening status and are easy to clean outside of the glass; when there’s a good day, they can be opened as normal inward casement windows.

Large Energy Efficient Fixed Windows

Our well-crafted bespoke systems enhance the functionality and panoramic view of this modern house.

Huge, fixed glass walls up to seven meters long and two meters high bring great lighting and open views, making it really refreshing to the mind. Five meters high long narrow windows give the whole building a contemporary aesthetic.

Every window’s placement and shape not only add to the uniqueness of this home but also provide a more energy-saving ability for the owners.

Doorwin energy-efficient integrated glazing units feature double-pane glass, warm-edge spacers, argon gas fill, Low-E coatings, and fully tempered glass, they can not only create a comfortable and natural indoor environment but also save electricity bills and heating bills of more than 100 USD for the owner, it’s a real bargain compared to choosing a regular glazing set.

Custom Designed Thermal Break Aluminum Entry Door

Aluminum Door offered an air of uniqueness and elegance to a home. With their luxurious patterns and beautiful finishes, it provides this house with a bounty of aesthetics and security. Aluminum entry doors allow you to resist any weather extremes, corrosion, and pests. So aluminum is one of the most resilient and durable materials you can select for front doors considering the price/performance ratio.

With pieces of double panes, and Low-E tempered glass. The door provides a good insulation performance.

Custom Designed Grilles and Transom

Divided lite windows and doors offer unique architectural solutions for buildings without compromising energy efficiency or aesthetics. Doorwin provides multiple muntin and glass options to customize your divided lite windows and doors. Further customization is available with a variety of colors and materials, creating an infinite number of design combinations to best suit your style.

In this project, we use SDLS (simulated divided lites with spacer bars), these bars permanently adhere to both sides of the glass, and spacer bars are installed between the glass, this is the most energy-efficient way to create the look of classical décor grilles. The windows in the bathroom bedroom and study have an Arch Transom Design, making these rooms, which are often used by the owner, have some traditional aesthetics.

BTW, Doorwin offers free design assistance, so if you need a custom design like this one, contact us right away and we will provide you with the most aesthetically and functionally pleasing design solution.

German Imported Hardware System

For windows and doors, hardware is as important as the engine is to the car. The continuous technological innovation of the European hardware industry has strongly promoted the performance improvement and functional innovation of windows and doors. In this project, Doorwin uses Hoppe™ multi-point locks, hinges, and handles from Germany.

Multi-point lock systems provide not only the burglar-resistance but also a tighter compression seam, making the window keeps good energy-efficient performance. Together with Technoform Bautec’s insulation edge bond and sealant strips, these make up our products' top insulation and energy-saving performance.

Save Your Money On Installation Costs

We have several international patents to reduce clients’ labor costs, such as our unique flanges and assembly type tubular design, which is different from the other products on the market. What sets us apart among Chinese counterpart is that all our products are equipped with nail fin structures for quick and easy installation. Labor costs during installation may exceed of the window and door price, therefore, our exclusive patent allows users to not only get a significant increase in installation efficiency, but also greatly reduce the labor cost of window and door installation. A cost that may bring you unexpected savings that far exceed the price difference you may care about now.

Free Design Assistance

With our own expertise, we provided the no-cost design development and contract documentation with CAD & BIM drawings, including elevation, details about the project, and installation help.

Before production, we will provide accurate sample drawings, which will clearly show the cross-sectional pattern, size, opening method and direction, pattern of the warm spacer, and the installation nodes. We will not go into production until you have signed off on the drawing to ensure that you receive a final product that meets the exact requirements of your project.

About Doorwin

Doorwin's professional packing system guarantees all products are delivered safely and without any damage. We apply a four-point packing system. Firstly, adhesive plastic film is applied on interior wood frames and exterior aluminum frames to avoid scratches on the surface. Then, a paper board is applied after we apply air bubble film surrounding the whole windows/ doors to avoid any destruction or clash. Lastly, we place them into a durable non-fumigation plywood crate to avoid any possible damage during transportation.

With years of experience shipping our products worldwide, we could guarantee to ship our products to their final destinations intact and without any damage.

About Doorwin Factories

Doorwin is one of the most professional window & door manufacturers are known for its great customized products. In Doorwin, a variety of colors, styles, and sizes of products are available to meet the client’s unique requirements. We own three ISO9000-certified modern factories in China. With a factory area of 20,000 m2 and a production capacity of 100,000 m2 per year. Doorwin Group has the scale to ensure timely delivery and the flexibility to reduce manufacturing lead times to as short as 18 days.