The Accenture Tower Curtain Wall Restoration: A Four-Year Plan
In 2021, real estate developer KBS contracted Western Specialty Contractors to undertake a comprehensive restoration of the original curtain wall at Accenture Tower, located at 500 West Madison Street in Chicago. The 42-story, 1.46 million square foot Class A office tower, completed in 1987, houses approximately 7,432 square meters (80,000 square feet) of retail space and sits above the Ogilvie Transportation Center. The building, formerly known as 500 West Madison, has twice earned the Outstanding Building of the Year (TOBY) award internationally from the Building Owner and Managers Association (BOMA) and holds LEED Gold, WiredScore Gold, and UL Verified Healthy Building certifications.
The project involves the systematic removal and replacement of the original sealants on the building’s curtain wall and the bridge structure extending over Canal Street. These sealants, now 35 years old, had reached the end of their service life and required complete replacement to maintain the building envelope’s performance against air infiltration and water intrusion. The work is relevant for building professionals working with curtain wall systems and facade restoration, as it demonstrates the scale, planning, and specialized techniques required for high-rise envelope renewal.
Understanding Curtain Wall Sealant Degradation in High-Rise Buildings
Curtain wall systems serve as the primary environmental barrier for modern high-rise structures. The sealants used in these systems perform several critical functions that degrade over time.
Why Sealants Fail After 25-35 Years
The original sealants in the Accenture Tower curtain wall had been in service since the building opened in 1987. After three and a half decades, exposure to Chicago’s freeze-thaw cycles, ultraviolet radiation, thermal expansion and contraction, and atmospheric pollutants had degraded the material’s elastic properties. Common failure modes include:
- Loss of adhesion at the sealant-to-substrate interface, creating pathways for water infiltration
- Hardening and embrittlement from UV exposure and oxidation, reducing movement capability
- Cohesive cracking within the sealant body as the material loses tensile strength
- Debonding at the heel of sealant joints where stress concentrations are highest
- Compression set from sustained loading, preventing the sealant from returning to original dimensions
Impact on Building Performance
When curtain wall sealants fail, the consequences extend beyond visible water staining. Degraded sealants compromise the entire building envelope performance in several measurable ways:
| Performance Factor | Impact of Failed Sealants | Restoration Benefit |
|---|---|---|
| Air Infiltration | Uncontrolled airflow increases HVAC load by 15-25% | Restored airtightness reduces energy consumption |
| Water Intrusion | Moisture penetration damages interior finishes and insulation | New sealants restore water barrier continuity |
| Thermal Performance | Gaps in the air barrier reduce effective R-value | Properly sealed assemblies maintain design thermal performance |
| Structural Integrity | Wind load transfer paths weaken at failed joints | Fresh sealant restores load distribution across panel joints |
| Indoor Air Quality | Mold growth from chronic moisture intrusion | Dry envelope conditions prevent biological growth |
Access Strategies for High-Rise Curtain Wall Restoration
One of the defining challenges of the Accenture Tower project is the physical access required to reach every portion of the curtain wall across 42 stories. The restoration team developed two complementary access strategies.
Maintenance House Rigs: Primary Access Solution
The Accenture Tower features two permanently installed maintenance house rigs. These remotely operated working platforms attach to the curtain wall’s structural tube members and internal track system. They function similarly to swing stages but are permanently integrated into the building infrastructure. These house rigs provide access to approximately 80 percent of the exterior facade. However, their use introduces specific constraints:
- Only two crews can work simultaneously because only two rigs are available
- The rigs do not reach the base of the building at street level
- The rigs cannot access the bridge structure over Canal Street
- Work sequencing must coordinate with rig movement patterns across each vertical run
Rope Access for Inaccessible Zones
For the 20 percent of the facade that the house rigs cannot reach, Western Specialty Contractors deployed an extensive rope access and controlled descent approach. This method provides the flexibility to work at the building base, along the Canal Street bridge, and in any configuration that falls outside the house rigs’ reach. The unitized curtain wall systems for high-rise buildings approach used in projects like the Raffles Boston demonstrates similar access considerations for facade maintenance in dense urban environments.
All Western employees performing rope access work on this project have completed training with certified evaluators from the Society of Professional Rope Access Technicians (SPRAT). They hold SPRAT Level 1: Rope Access Worker certification, ensuring elevated safety standards for work performed at significant heights.
Material Selection and Sealant Specification for Curtain Wall Restoration
Selecting the correct replacement sealant for a 35-year-old curtain wall system requires careful evaluation of substrate compatibility, performance requirements, and application conditions.
Key Specification Criteria
The replacement sealants for a project of this scale must meet several performance benchmarks:
- Movement capability: The sealant must accommodate the building’s anticipated thermal and structural movements, typically rated at 50 percent or greater movement in both tension and compression
- Adhesion to aged substrates: The existing aluminum and glass substrates may have surface conditions different from new construction, requiring specific primers or surface preparation
- Weathering resistance: Sealants must maintain performance through Chicago’s extreme temperature range from well below freezing in winter to over 38 degrees Celsius in summer
- Color stability: The restored curtain wall must present a uniform appearance, requiring color-matched sealants across all 42 stories
- Cure time: Work scheduling must account for sealant cure windows, particularly in variable weather conditions at height
Substrate Preparation for Sealant Adhesion
The success of any curtain wall restoration depends on proper surface preparation before new sealant application. The removal of old sealant leaves behind residue that must be completely cleaned. The preparation sequence includes:
- Mechanical removal of bulk old sealant material using non-abrasive tools that will not damage the aluminum or glass surfaces
- Chemical cleaning to remove any remaining sealant film and oxidation
- Solvent wiping immediately before sealant application to ensure uncontaminated adhesion surfaces
- Primer application where specified, with strict attention to coverage consistency and flash-off time
- Environmental condition verification including substrate temperature, air temperature, and humidity within manufacturer-specified ranges
These preparation requirements are similar to those used in new construction, where glass facade specifications and application strategies emphasize the importance of surface preparation for long-term envelope performance. The integration of weather-resistant barrier specifications for building envelope moisture management further reinforces the principle that sealant quality depends as much on surface preparation as on the sealant material itself.
Lessons for Building Professionals Planning Curtain Wall Restoration
The Accenture Tower project offers several takeaways for architects, specifiers, and building owners planning their own curtain wall restoration programs.
Timing the Restoration Cycle
The 35-year service life of the original Accenture Tower sealants aligns with industry expectations for high-performance curtain wall sealants. Building owners should plan for major sealant replacement at 25- to 35-year intervals, with regular inspection and localized repairs in the intervening years. Key planning considerations include:
- Conducting diagnostic testing of sealant samples at year 20 to establish baseline condition data
- Budgeting for complete replacement at year 25 and adjusting based on inspection findings
- Scheduling restoration work during favorable weather seasons to maximize sealant application windows
- Coordinating with tenant improvement cycles to minimize disruption to occupied spaces
- Verifying that replacement sealants are compatible with the original framing system and adjacent materials
The Value of Advanced Access Planning
The Accenture Tower project demonstrates that dual access strategies (house rigs plus rope access) can effectively cover 100 percent of a complex facade geometry. Building professionals designing new buildings should consider incorporating maintenance access provisions into the original curtain wall design, such as integrated track systems and anchorage points for rope access. These provisions significantly reduce the cost and complexity of future envelope renewal work.
For building owners and property managers evaluating restoration options, the combination of permanent rigging systems with trained rope access teams represents a proven approach that minimizes disruption while maximizing coverage. The SPRAT certification program ensures that rope access workers meet nationally recognized safety standards, making this an accessible option for facade contractors across the country.