Retrofit Windows for Historic Buildings: Preserving Design While Improving Performance
How Retrofit Windows Preserve Historic Architecture While Improving Performance
Commercial and architectural retrofit window projects are often undertaken to improve energy efficiency, occupant comfort, and long-term building performance. In historic structures, however, window retrofits must do more. They need to preserve original design intent while meeting modern thermal and operational standards.
This case study explores how a historic Nashville landmark achieved those goals using custom retrofit windows built with Quanex Duralite® warm-edge spacer technology.
What Are Retrofit Windows and Why Are They Used?
Retrofit windows are replacement window systems designed to integrate into existing building openings rather than requiring full removal of the original structure. This approach allows building owners and architects to modernize performance while minimizing disruption to the building envelope.
In commercial and institutional settings, especially older buildings, retrofit windows are often preferred because they reduce construction time, material waste, and occupant impact while still delivering meaningful energy improvements.
How Retrofit Windows Differ From New-Construction Windows
Unlike new-construction windows, retrofit windows are engineered around existing conditions. This requires precise customization to ensure proper fit, performance, and appearance.
Retrofit window solutions typically:
- Work within existing frames or masonry openings
- Require less demolition and structural modification
- Allow faster installation in occupied buildings
- Support phased or large-scale replacement projects
Because of these advantages, retrofit windows are widely used in schools, government buildings, and legacy commercial structures.
Why Retrofit Windows Are Ideal for Historic Buildings
Historic buildings present unique challenges that go beyond performance alone. Architects must balance energy codes, preservation guidelines, and aesthetic requirements, often under the scrutiny of preservation boards or historical commissions.
Retrofit windows offer a solution that respects the original architecture while addressing modern expectations.
Preserving Architectural Integrity While Improving Performance
One of the primary benefits of retrofit windows in historic applications is their ability to replicate original window styles, proportions, and sightlines. This allows buildings to retain their historic character while benefiting from modern glazing technologies.
Key advantages for historic projects include:
- Preservation of original facade appearance
- Consistent sightlines and profiles
- Improved thermal and acoustic performance
- Enhanced comfort without visual compromise
When designed correctly, retrofit windows can be nearly indistinguishable from the originals, while performing at a much higher level.
Real-Life Application: Retrofit Windows at Hume-Fogg Magnet High School
Originally constructed in 1855, Hume-Fogg Magnet High School was Nashville’s first operating public school and remains an active educational facility today. Known for its Gothic Revival architecture, the building is both historically significant and heavily occupied.
In late 2018, the school undertook a full-building retrofit window project aimed at improving energy efficiency while preserving its architectural identity and beauty.
Custom Retrofit Windows Designed for a Historic Landmark
The project utilized fully custom casement retrofit windows manufactured by Sun Windows & Doors, a third-generation, family-owned company specializing in built-to-order solutions for commercial and architectural projects.
To ensure historical accuracy, Sun referenced the building’s original blueprints to replicate the original window styles and proportions. The final solution included a mix of fixed and operable casement windows designed to maximize visible light transmission while minimizing reflection.
Manufacturer Perspective: Performance Without Compromise
According to Sun Windows & Doors, achieving modern performance without altering the historic character of the building was a core requirement of the project.
“Our customers expect improved thermal performance, especially in retrofit projects like this, but they don’t want to sacrifice architectural integrity,” said Frank Anderson, President of Sun Windows & Doors. “Using Quanex Duralite warm-edge spacer technology allows us to deliver both strong energy performance and clean, historically appropriate sightlines.”
Performance Results Achieved
- Fixed units achieved a U-factor of 0.30
- Operable units achieved a U-factor of 0.34
- Enhanced comfort and reduced energy loss
These results were made possible by incorporating Duralite warm-edge spacer technology into the insulating glass units.
Why Duralite® is a Smart Choice for Retrofit Window Projects
For architects and window (and door) manufacturers working on retrofit windows, particularly in historic buildings, the spacer system plays a critical role in overall performance. Duralite from Quanex is a non-metal warm-edge spacer system designed to reduce heat transfer at the edge of glass, one of the most vulnerable areas in an IG unit.
Thermal Performance and Design Benefits of Duralite
Duralite’s composite construction creates a warmer edge-of-glass temperature, improving condensation resistance and overall energy efficiency without adding visual bulk.
Key benefits for retrofit window applications include:
- Superior argon gas retention
- Improved condensation resistance
- Smooth, subtle sightlines suitable for historic designs
- Long-term durability and thermal stability
Because Duralite is applied in a single step and comes preassembled with sealant and desiccant, it also supports efficient production for custom retrofit window projects.
Supporting Architects and Manufacturers From Design to Installation
Beyond product performance, Quanex supports retrofit window manufacturers with technical expertise, production setup assistance, and ongoing quality audits. For this project, that support helped ensure consistent IG quality across all units while meeting tight installation timelines in a high-traffic, occupied building.
The result was a 90-business-day project, completed with minimal disruption, through close collaboration between the architect, builder, dealer, and window manufacturer.
In addition to product performance, Sun Windows & Doors values Quanex as a technical partner throughout the manufacturing process.
“Quanex brings more than a component, they bring expertise,” said Anderson. “From helping us optimize our insulating glass production to providing ongoing quality audits, their support helps ensure we’re delivering the highest-quality IG units possible on every project.”
Article Updated: 11 FEB 2026
Partner With Quanex on High-Performance Windows
Let’s talk about your retrofit window project (or any other window project)
Architectural retrofit window projects, especially those involving historic or legacy buildings, require more than standard components. They demand proven technologies, deep technical expertise, and partners who understand how performance, design, and production intersect.
At Quanex, we work closely with architects, specifiers, and window and door manufacturers to support projects from concept through completion. Our Duralite warm-edge spacer technology is engineered to help preserve architectural intent while delivering the thermal performance today’s buildings require.
Whether you’re:
- Designing retrofit windows for a historically significant building
- Specifying high-performance insulating glass systems
- Manufacturing custom windows at scale
Our team is ready to help you evaluate solutions, optimize performance, and meet project-specific requirements with confidence.
Complete the form below to connect with a Quanex representative and start a conversation about how Duralite can support your next retrofit window project.
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