Preservation Brief 13 Explained: Repair and Thermal Upgrading of Historic Steel Windows
Why Some of the Most Durable Windows Ever Made Are Also Among the Most Misunderstood
Walk through a historic school in Tampa, university campus in Alabama, a courthouse in Nashville, industrial building in Orlando, or mid-century civic structure, and there is a good chance you'll encounter steel windows.
Often slender and elegant, these windows became popular throughout the early and mid-20th century because they allowed architects to achieve larger glass areas, narrower sightlines, and more daylight than traditional wood systems.
Today, many of those same windows face a familiar challenge. Property owners look at rust, air infiltration, worn hardware, or broken glass and assume replacement is inevitable. Preservation Brief 13 takes a different view.
Published by the National Park Service, Preservation Brief 13: The Repair and Thermal Upgrading of Historic Steel Windows remains one of the most important resources available for understanding how steel windows can be repaired, upgraded, and preserved. Like Preservation Brief 9 for wood windows, Preservation Brief 13 starts with a simple premise:
Many historic steel windows are far more repairable than they appear.
For architects, building owners, preservation consultants, and contractors, understanding that principle can dramatically change how projects are evaluated and scoped.
What Is Preservation Brief 13?
Preservation Brief 13 was developed by the National Park Service to provide technical guidance for the repair and thermal improvement of historic steel windows.
The full document can be found here:
Preservation Brief 13: Repair and Thermal Upgrading of Historic Steel Windows
The brief focuses on:
identifying deterioration
evaluating repair options
improving performance
preserving historic character
determining when replacement may be appropriate
While originally written decades ago, the guidance remains highly relevant for today's preservation and adaptive reuse projects.
Why Historic Steel Windows Matter
Unlike wood windows, steel windows are often underestimated because corrosion is highly visible. Rust can look alarming. But appearance and structural condition are not always the same thing.
Historic steel windows were commonly fabricated from rolled steel sections and engineered for durability. Many have survived for decades despite:
weather exposure
deferred maintenance
building vacancy
changing ownership
repeated paint cycles
Beyond durability, steel windows contribute significantly to a building's architectural identity. Their defining characteristics often include:
exceptionally narrow sightlines
large glass areas
distinctive muntin profiles
industrial craftsmanship
period-specific detailing
In many historic buildings, replacing steel windows fundamentally changes the appearance of the façade. That is one reason preservation review agencies frequently examine steel window treatment carefully.
Rust Does Not Automatically Mean Failure
This may be the single most important takeaway from Preservation Brief 13. Owners often see rust and assume the window is beyond repair. In reality, corrosion exists on a spectrum.
Surface rust may require little more than:
cleaning
preparation
protective coatings
More advanced deterioration may require:
localized steel repairs
component replacement
welding
fabrication
The brief encourages teams to assess actual structural condition rather than relying solely on visual appearance. Many steel windows that appear severely deteriorated remain viable candidates for restoration.
Understanding Common Steel Window Problems
Preservation Brief 13 identifies several recurring conditions.
Corrosion
The most obvious issue. Typically caused by:
coating failure
prolonged moisture exposure
deferred maintenance
Failed Putty and Glazing
Like wood windows, steel systems rely on glazing materials to secure and protect glass. As glazing deteriorates, moisture can infiltrate and accelerate corrosion.
Hardware Failure
Historic steel windows often include:
hinges
operators
locking systems
friction hardware
These components may wear over time but are frequently repairable or replaceable without having to replace the window assembly.
Air Infiltration
Many older steel windows were not designed with modern air-sealing expectations. Fortunately, performance improvements are often possible without replacement.
The Preservation Brief's Approach to Repair
One reason Preservation Brief 13 remains valuable is that it focuses on practical repair strategies. The document encourages retaining as much original material as possible while addressing deterioration appropriately.
Potential repairs may include:
rust removal
steel stabilization
welding repairs
hardware rehabilitation
glazing replacement
repainting
weatherstripping
The goal is not perfection. The goal is extending service life while preserving historic character.
Thermal Upgrading Without Replacement
The word "thermal" in the title often surprises people. After all, historic steel windows are frequently criticized for poor energy performance. Preservation Brief 13 directly addresses this concern. Rather than assuming replacement is the only solution, the document explores methods for improving performance while retaining original windows.
Potential strategies include:
Weatherstripping
Reducing air infiltration can significantly improve comfort.
Storm Windows
Both interior and exterior storm systems may improve performance while preserving historic fabric.
Glazing Improvements
Depending on project requirements and preservation constraints, glazing enhancements may be possible.
Operational Restoration
A properly functioning window often performs better than one that has been neglected for decades. These strategies frequently allow project teams to improve performance without sacrificing architectural character.
Why Replacement Is Often More Complicated Than It Appears
Steel windows present unique replacement challenges. Their profiles are typically much slimmer than modern alternatives. As a result, replacement systems often introduce:
wider frames
altered sightlines
different reflectivity
changed proportions
To casual observers these differences may seem minor. On a historic façade, however, they can dramatically affect appearance. This is particularly important for:
universities
government buildings
historic schools
adaptive reuse projects
tax credit developments
Preservation reviewers often focus heavily on these visual impacts.
When Replacement May Be Appropriate
Preservation Brief 13 does not prohibit replacement. There are situations where replacement or replication becomes necessary. Examples include:
severe structural deterioration
extensive section loss
missing assemblies
conditions beyond practical repair
The key is evaluation. The brief encourages project teams to understand existing conditions thoroughly before concluding that replacement is required. Historically compatible replication may also provide an appropriate solution when original assemblies cannot reasonably be saved.
Why This Matters for Tax Credit Projects
For teams pursuing historic tax credits, Preservation Brief 13 is particularly important. Steel windows are often considered character-defining features. As a result, reviewers frequently evaluate:
repair feasibility
material retention
profile preservation
visual impact
Projects that begin with restoration assessments often experience fewer surprises during review than those that start with replacement assumptions.
Lessons for Architects and Building Owners
Perhaps the most valuable lesson from Preservation Brief 13 is that steel windows deserve the same thoughtful evaluation as historic wood windows. Too often, corrosion becomes a reason to skip directly to replacement.
The brief reminds us that:
deterioration can often be repaired
performance can often be improved
historic character can often be preserved
Those outcomes are not mutually exclusive. With proper assessment and planning, project teams can frequently achieve all three.
Final Thoughts
Historic steel windows occupy a unique place in preservation. They combine engineering, craftsmanship, and architectural character in a way few building components can.
Preservation Brief 13 remains relevant because it recognizes something that experienced preservation professionals see regularly:
Many steel windows that appear worn out are simply waiting for someone to look beyond the rust.
When evaluated thoughtfully, repaired appropriately, and upgraded strategically, historic steel windows can continue serving buildings for generations while preserving the architectural character that makes those buildings significant.
That is ultimately what Preservation Brief 13 encourages—and why it remains one of the most important resources in the preservation community.
