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Restoring a historic exterior is a diagnosis-and-repair job, not a cosmetic facelift. The successful approach is to determine which fabric is sound, stabilize what is unsafe, repair as much original material as practical, and replace only what has failed—while matching the old building’s profiles, colors, tooling and proportions. Two projects described by Building Design + Construction show how different that process can be: Philadelphia’s City Hall Annex needed systematic envelope renewal before conversion to a hotel, while New York City’s Tweed Courthouse required major stone replacement and temporary structural protection.
The account, published August 11, 2010, is a historical project record rather than current code guidance or a present-day price list. Its methods and quantities are useful because they make the decisions visible: assess the existing structure, separate repair from replacement, reproduce details accurately, protect the work from weather, and coordinate conservation with a new use.
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A historic building envelope is a system of masonry, terra cotta, stone, metals, windows, roof coverings, joints and attachments. Water entering at one failed joint can damage several materials, while an unsafe projecting element can make an apparently sound façade a public hazard. Exterior restoration therefore combines investigation, temporary works, skilled repair and selective reconstruction.
The two case studies had different starting points. The 1926 City Hall Annex in Philadelphia was a 17-story, 356,000-square-foot building that had stood vacant for about a decade. Its limestone and terra-cotta façade was described as generally structurally sound, although some steel members needed repair. The Tweed Courthouse, erected over a 20-year period beginning in 1861, had severely deteriorated projecting cornice stones and other damaged façade elements; portions had to be fenced off and stabilized with shoring towers.
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In both projects, the new use made continued preservation possible. The Annex was converted into a 498-room Courtyard by Marriott hotel. Tweed was restored and reused as a museum under the New York City Economic Development Corp. The work shows that reuse does not mean freezing a building in place. It means making the envelope safe, weather-tight and serviceable without erasing its historic character.
Start with a condition assessment, not a replacement schedule
Map each material and failure mode
Before selecting products or contractors, document the façade by material and elevation. Look for cracked or displaced stone, open or failed mortar joints, corrosion at embedded steel, water stains, failed roof drainage, loose projections and missing decorative pieces. Sounding, close visual inspection, probes at representative joints and records of prior repairs help distinguish surface dirt from structural distress. The 2010 account does not provide a universal survey protocol; it demonstrates why the scope must follow actual conditions.
Separate urgent hazards from repairable deterioration
Loose cornice stones, unstable terra-cotta units and corroded supports require immediate controls such as exclusion zones, shoring or temporary attachment. Cosmetic discoloration can wait until the building is safe. At Tweed, deteriorated projections were serious enough that areas were fenced off and shoring towers were erected. That sequence—protect people first, then investigate and repair—is more important than any particular cleaning method.
Test cleaning and repointing before full production
Historic masonry and bronze can be damaged by an overly aggressive treatment. Establish small test panels, record pressure and dwell times, and confirm that the trial removes soiling without eroding tooling, widening joints or stripping protective finishes. Repointing should be based on the existing masonry and joint behavior; the article reports that roughly half of the Annex’s masonry joints were repointed, not that every joint was automatically removed.
Philadelphia City Hall Annex: renewing a mostly sound envelope
Scope of the 1926 building
The Annex stood beside Philadelphia City Hall and had a leaking asphalt roof, cracking limestone and terra-cotta façades, and bronze details covered by accumulated patina. Because the primary envelope was generally sound, the project could emphasize cleaning, localized structural work and replacement of worn components rather than wholesale façade reconstruction.
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Masonry, bronze and steel repairs
Crews cleaned the façade and repointed about 50 percent of the masonry joints. Missing bronze details were replaced, while existing bronze was stripped, refinished and cleaned. A few structural steel members were repaired. This combination matters: decorative metal treatment, joint renewal and structural repairs were coordinated instead of treating the façade as a single interchangeable skin.
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A soda-based cleaning method for metal
Thomas Neider, senior project manager with Gilbane Building Co., described the metal-cleaning approach: “Instead of using a traditional chemical stripper, we sprayed at high pressure a solution made of baking soda followed by water,” he says. The quotation describes this project’s method; it is not a blanket recommendation for every historic metal surface. A conservator should verify substrate, coating and runoff controls before specifying any abrasive or high-pressure process.
Replacing 1,000 windows without losing the elevations’ rhythm
The Annex’s 1,000 steel windows were replaced with custom-fabricated aluminum units. Fabricators replicated eight original profiles and colors so the new frames would read like the historic windows from the street. The article reports approximately $1.7 million for this window replacement work in 2010. The result illustrates a key preservation trade-off: the material changed, but sightlines, divisions and color cues were retained.
Why the project installed a new roof
The existing asphalt roof was about 15 years old and could probably have been repaired. The team chose a new EPDM roof system so the roof would have a new service life alongside the restored façade. Neider explained the reasoning: “We probably could have repaired the roof, which was about 15 years old,” he concludes. “But we decided that since the façade was being restored like new, then the roof should have a new face too.” The decision was project-specific, balancing remaining roof life against the cost and disruption of returning later to replace it.
Tweed Courthouse: stabilizing and rebuilding severely damaged stonework
When repair is no longer enough
Tweed’s projecting cornice had deteriorated to the point that parts of the property were unsafe. Donald Curtis, senior manager with Bovis Lend Lease, said: “Various parts of the building had deteriorated so badly that portions of the property were fenced off and shoring towers erected to stabilize the overhanging projections.” The statement captures the difference between a maintenance repair and an emergency stabilization operation.
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Removing the cornice and sourcing replacement stone
The entire cornice, reported as 2.5 million pounds of stone, was removed. The project required about 4 million pounds of new stone for the cornice and other damaged façade elements. Replacement cornice pieces used Georgia Cherokee marble. The article also reports that replacement elements were cut from old cornice stones and from 115 untouched blocks found at the original quarry in Sheffield, Massachusetts. Reuse of salvaged material and carefully matched new stone allowed the rebuilt work to align with the historic design while addressing the quantity of failed fabric.
Recreating carved ornament
Some leaves on the column capitals had deteriorated and had been chipped off during maintenance in the 1940s. Jack Waite, principal of John G. Waite Associates, explained: “These leaves started deteriorating in the 1940s, so the maintenance people chipped them off,” he says. “Craftsmen are now carving new leaves, which are pinned and glued into place.” The process combines hand carving with mechanical attachment; it does not pretend that every original fragment can be recovered.
Rebuilding the roof over existing iron trusses
The recreated roof used 24-gauge zinc-coated stainless-steel corrugated panels over EPDM installed on the existing iron trusses. A custom temporary roof and scaffolding protected the façade work from weather and provided support while replacement stones were handled. The reported temporary roof covered 75,000 square feet. Temporary works were therefore part of the conservation design, not merely a contractor’s convenience.
How the two restoration strategies differ
| Decision point | City Hall Annex, Philadelphia | Tweed Courthouse, New York City |
|---|---|---|
| Initial condition | Limestone and terra-cotta façade generally structurally sound; leaking roof, cracked finishes, weathered bronze and a few steel members needing repair. | Severely deteriorated projecting cornice and other damaged stone; unsafe areas required fencing and shoring. |
| Primary exterior work | Façade cleaning, repointing about 50% of joints, bronze cleaning/refinishing/replacement, localized steel repair, window replacement and a new roof. | Complete cornice removal, large-scale stone replacement, carved ornament reconstruction and a recreated roof. |
| Replacement strategy | Custom aluminum windows reproduced eight original steel-window profiles and colors. | Georgia Cherokee marble, salvaged historic stone and blocks from the original Sheffield quarry were used for replacement elements. |
| Roof assembly reported | New EPDM roof system over the restored building. | 24-gauge zinc-coated stainless-steel corrugated panels over EPDM on existing iron trusses. |
| Weather and access controls | Not detailed in the account. | Custom temporary roof and scaffolding protected work and supported replacement stone; temporary roof area was 75,000 square feet. |
These examples are not universal specifications. They show how the existing condition determines the balance between cleaning, repair, replacement and reconstruction.
What the reported costs do—and do not—tell you
All figures below come from the August 11, 2010 Building Design + Construction report and are historical project figures, not inflation-adjusted budgets or current bids.
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- The City Hall Annex restoration was reported at $67 million.
- Its window replacement work was reported at approximately $1.7 million.
- The Tweed Courthouse restoration and reuse project was reported at $80 million.
- Tweed stonework was estimated at $16.5 million.
Those totals combine different scopes, dates and market conditions. They should not be used to price another building by square foot. A current estimate would need investigation results, access and protection requirements, labor rates, material availability, code upgrades, hazardous-material controls, design fees, contingency and the proposed use.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical sequence for planning an exterior restoration
- Define the historic significance and the new use. Identify character-defining elevations, ornament, openings, roof lines and materials before designing alterations for occupancy.
- Survey and record conditions. Prepare elevation drawings and photographs, map cracks and open joints, inspect roofs and drainage, and document previous patches or replacements.
- Make unsafe areas safe. Use fencing, shoring, temporary anchors or other engineered measures where stones, terra cotta or metal projections could fall.
- Develop and approve test panels. Test cleaning, repointing, coating removal and repair samples on representative areas; retain records of the accepted method.
- Choose repair before replacement. Retain sound original material, repair localized steel or masonry, and replace only units that cannot meet safety or performance requirements.
- Match replacements deliberately. Match profiles, colors, dimensions, tooling and attachment details. The Annex’s eight window profiles and Tweed’s carved leaves show that visual accuracy includes small elements.
- Coordinate roof and façade decisions. Decide whether the roof’s remaining life justifies repair or whether replacing it during façade work avoids a second major mobilization.
- Design temporary works into the program. Plan scaffolding, weather protection, lifting routes and stone storage before removing large or projecting elements.
- Inspect and document completed work. Record replaced units, hidden anchors, joint treatments, roof transitions and maintenance requirements so future owners can distinguish original fabric from interventions.
Common pitfalls and how these projects help avoid them
- Replacing everything because it is old. The Annex retained a generally sound façade and focused on targeted repairs; age alone did not determine removal.
- Ignoring hidden structural conditions. A clean surface can conceal failed steel or unsafe projections. Localized steel repairs at the Annex and shoring at Tweed show why investigation must include supports and attachments.
- Treating ornament as optional. Missing bronze details, window profiles and carved leaves affect the building’s reading. Record and reproduce significant details rather than accepting generic components.
- Starting demolition without weather protection. Tweed’s temporary roof and scaffolding limited exposure while the cornice and roof were rebuilt.
- Using historical prices as current allowances. The published 2010 figures are useful for understanding scope, not for setting a 2026 budget.
- Assuming one cleaning method fits all materials. The baking-soda method was described for the Annex’s metal work; masonry, terra cotta, stone and bronze each require compatible testing and runoff control.
What is established—and what remains project-specific
The published account establishes the quantities, materials, quoted decisions and reported costs for these two projects. It does not provide current preservation standards, present-day product specifications, measured energy or water-performance results, or a maintenance record after completion. It also does not establish that EPDM, custom aluminum windows, Georgia Cherokee marble or any cleaning process is the right choice for another building.
For a live project, the owner should assemble a preservation architect, structural engineer, envelope specialist, conservator and contractor with relevant historic-fabric experience. Their recommendations should be based on the building’s survey, jurisdictional requirements, intended occupancy and the reversibility and durability of proposed interventions.
Source and historical context
The case details and quotations are from Building Design + Construction, “A fresh old face,” published August 11, 2010. Philadelphia’s Annex and New York’s Tweed Courthouse demonstrate two ends of the same principle: an aging exterior can often be made safe and useful through careful repair, selective replacement and compatible new work instead of automatic demolition.
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