When the owners of the landmark Carson Building — a 12-story Beaux-Arts office tower completed in 1924 on Chicago's Michigan Avenue — needed to replace their deteriorating original steel windows, they faced a dilemma that confronts many historic property owners: how do you achieve modern energy performance and occupant comfort without compromising the architectural character that makes the building special?

The answer, as it turned out, was a custom-engineered steel glazing system from Precision Door & Window Manufacturer — designed to match the original sightlines and aesthetic character while delivering 21st-century thermal performance.

The Challenge

The Carson Building's original windows were single-glazed steel units set into a masonry structure. While beautiful, they were thermally inefficient, drafty, and in many cases rusted beyond repair. The building's landmark status meant that any replacement would need to be approved by the Chicago Historic Preservation Commission — requiring historically accurate sightlines, profiles, and finishes.

Key requirements included:

• Maintain the original 22mm sightline width — a dimension far narrower than standard modern steel profiles
• Match the original dark bronze patina finish
• Achieve a U-value of at least 1.4 W/m²K — a 60% improvement over the original glazing
• Accommodate 42mm insulated glass units within slim steel frames
• Complete the installation while the building remained partially occupied

Our Engineering Approach

Our engineering team began with a detailed 3D laser scan of the existing window openings — all 340 of them. This allowed us to account for nearly a century of building settlement and create a digital model that precisely documented every variation in opening dimensions.

From this model, we designed a custom steel profile that achieved a 22mm sightline while incorporating:

• A precision-welded tubular steel frame for structural integrity
• A thermal break integrated into the glazing pocket rather than the frame — a novel approach that preserved the slim aesthetic
• Custom-cast corner joints that matched the original building's detailing
• A three-stage zinc primer and polyester powder coat system matched to the original bronze patina

"This project demanded that we push our manufacturing capabilities to their limits. Every one of those 340 openings was slightly different. It was essentially a custom fabrication job — and that's where our expertise really shines." — Dr. James Walker, Director of Engineering

Installation and Results

Installation was completed over a 10-month period, with work sequenced floor by floor to minimize disruption to tenants. Our installation team worked closely with the general contractor to coordinate with ongoing interior renovations.

The final results exceeded expectations:

• Achieved U-values of 1.2–1.4 W/m²K across all window types — exceeding the project requirement
• Reduced the building's annual HVAC energy consumption by an estimated 35%
• Received unanimous approval from the Chicago Historic Preservation Commission
• Won a 2026 AIA Chicago Design Excellence Award for Historic Preservation

What This Means for Historic Retrofit Projects

The Carson Building project demonstrates that historic preservation and modern energy performance are not mutually exclusive. With advanced manufacturing techniques and a willingness to engineer custom solutions, even the most demanding historic requirements can be met without aesthetic compromise.

If you're planning a historic retrofit project, our team would be happy to discuss how we can help. We offer comprehensive technical consultation, including energy modeling, 3D scanning, and custom profile design.