Adaptive Reuse of Mid-Century Office Buildings: Converting the Oncor Building and Beyond

The conversion of aging commercial properties continues to reshape urban skylines across North America, and few projects illustrate the potential of this movement more vividly than the ongoing adaptive reuse of the Oncor Building in downtown Fort Worth, Texas. The 27,871-square-meter (300,000-square-foot) former office tower is being transformed into a mixed-use destination through a carefully orchestrated demolition and redevelopment process. For construction professionals, architects, and developers, this project offers practical lessons in how adaptive reuse strategies for mid-century office buildings can breathe new life into underperforming assets while preserving urban character and reducing embodied carbon.

Why Adaptive Reuse Is Reshaping Commercial Real Estate

The economics of commercial real estate have shifted dramatically since the pandemic. Office vacancy rates in many downtown cores have climbed above 20 percent, and building owners face a stark choice: reposition their assets or watch them decline in value. Adaptive reuse has emerged as the preferred strategy for many of these properties, combining sustainability benefits with financial returns that often exceed ground-up construction.

The Case for Retention over Demolition

Demolishing an existing structure and building anew consumes enormous resources. A 2024 study from the Preservation Green Lab found that reusing an existing building can reduce climate change impacts by 20 to 40 percent compared to new construction over a 75-year lifespan. When a structure as substantial as the Oncor Building is involved, the embodied energy savings are significant. The concrete frame, steel reinforcement, and foundation systems represent millions of dollars in embedded material that would otherwise end up in a landfill.

Beyond the environmental case, adaptive reuse often allows developers to bypass lengthy permitting processes. Many municipalities have begun streamlining approvals for adaptive reuse projects as part of broader downtown revitalization efforts. In Fort Worth, the city has actively supported the Oncor Building transformation through zoning adjustments and tax incentives, recognizing that the project will bring new residents and visitors to the urban core.

Economic Drivers Behind the Trend

The financial case for adaptive reuse continues to strengthen as construction costs rise. Key economic factors include:

• Lower core and shell costs: Existing foundations, structural frames, and building envelopes typically represent 25 to 35 percent of total project costs that are already in place.
• Faster project timelines: Adaptive reuse projects can reach completion 12 to 18 months faster than new construction, accelerating return on investment.
• Premium rental rates: Spaces with exposed brick, high ceilings, and historic character command 15 to 25 percent higher rents in many markets.
• Tax incentives: Federal and state historic preservation tax credits can offset 20 to 40 percent of qualified rehabilitation costs.

These factors combine to create a compelling investment thesis for developers willing to tackle the complexities of working within an existing structure.

The Oncor Building: A Case Study in Mid-Century Office Conversion

The Oncor Building, originally constructed as a corporate headquarters for a major utility company, embodies the design principles of mid-century commercial architecture. Its wide floor plates, robust structural grid, and centralized mechanical systems were ideal for 1960s-era open-plan offices but present specific challenges for modern mixed-use programming.

Structural Adaptations Required

Converting a mid-century office building into a mixed-use property requires substantial structural modifications. The Oncor project team identified three critical areas requiring intervention:

1. Floor plate reconfiguration: The original 2,000-square-meter floor plates needed to be subdivided for residential units. This required installing new party walls, upgrading fire separation assemblies, and creating new egress paths that meet current building codes.
2. Core drilling for new MEP systems: Modern residential units demand individual HVAC, plumbing, and electrical services. The team is core-drilling through existing concrete slabs to route new risers, a process that demands precise coordination to avoid compromising the existing post-tensioned slab system.
3. Window wall replacement: The original single-glazed curtain wall system is being replaced with high-performance insulated glazing units. This upgrade improves thermal performance by approximately 60 percent while maintaining the building’s distinctive mid-century aesthetic.

Construction Sequencing and Phasing

One of the most challenging aspects of adaptive reuse is staging construction work while maintaining safety and efficiency. The Oncor project is being executed in four overlapping phases:

This phased approach allows the development team to deliver residential units to market incrementally, generating revenue before the entire project is complete. It also reduces the risk profile by allowing the team to validate construction methods in early phases before scaling them across the building.

Design Considerations for Office-to-Residential Conversions

Deep floor plates designed for office use present distinctive design challenges when converted to residential occupancy. Natural light penetration becomes critical, and unit layouts must be carefully planned to ensure every room has access to windows. The office-to-residential conversion strategies employed on the Oncor project include inserting light courts, creating atrium spaces, and positioning living areas along the perimeter with service cores toward the building interior.

Unit Mix and Programming

Successful adaptive reuse projects carefully calibrate their unit mix to match market demand. The Oncor Building conversion includes:

• Studio units (25 percent of total) targeting young professionals and remote workers
• One-bedroom units (40 percent) for couples and single tenants seeking more space
• Two-bedroom units (25 percent) for roommates and small families
• Penthouse and amenity spaces (10 percent) on the upper floors with city views

This mix diversifies the tenant base and reduces vacancy risk. The ground floor is being programmed with retail, restaurant, and co-working spaces to activate the street level and create a sense of community within the building.

Sustainability and Energy Performance

Adaptive reuse projects present a unique opportunity to dramatically improve the energy performance of existing buildings. The Oncor conversion targets a 45 percent reduction in energy use intensity compared to the building’s pre-renovation baseline through several key interventions:

• High-performance curtain wall replacement with thermally broken frames
• Variable refrigerant flow HVAC systems with heat recovery for zone-level control
• LED lighting throughout with daylight-responsive controls in common areas
• Low-flow plumbing fixtures projected to reduce water consumption by 35 percent
• Roof-mounted photovoltaic array offsetting 15 percent of common area electricity

These measures position the building to achieve LEED Gold certification, adding to its market appeal among environmentally conscious tenants.

Lessons for Construction Professionals Working on Adaptive Reuse

Adaptive reuse projects demand a different approach than new construction. The unknowns hidden within existing structures require flexible contracts, thorough preconstruction investigation, and collaborative teamwork. Historic adaptive reuse projects like Seattle’s Metropole Building have demonstrated that thorough documentation and contingency planning are essential for success.

Preconstruction Investigation Protocols

Before breaking ground, the Oncor team invested heavily in preconstruction investigation. This included:

• Selective exploratory demolition at 12 locations throughout the building to verify as-built conditions against available drawings
• Concrete core sampling to test compressive strength and assess chloride ingress in the parking structure
• Infrared thermography of the entire building envelope to identify thermal bridging and moisture intrusion points
• 3D laser scanning of all floors to create an accurate BIM model for clash detection and material takeoffs

This upfront investment paid for itself when the team discovered undocumented post-tensioning tendons in the fourth-floor slab during scanning. The discovery allowed the team to reroute planned MEP penetrations before construction, avoiding a costly field change.

Contract and Risk Management Strategies

Standard lump-sum contracts are poorly suited to adaptive reuse projects, where the extent of unknown conditions can upend budgets and schedules. The Oncor project uses a hybrid contract structure that includes:

• A guaranteed maximum price with shared savings provisions to incentivize value engineering
• Unit prices for selective demolition, concrete coring, and hazardous material abatement
• A contingency allowance of 12 percent of the construction budget specifically allocated for unknown conditions
• Monthly risk review meetings where the owner, architect, and contractor review emerging issues and adjust the contingency drawdown plan

This approach has allowed the project to absorb several unexpected findings without triggering formal change order disputes. Large-scale hospital adaptive reuse projects like SOM’s Cook County Hospital revitalization have proven that flexible delivery methods are key when converting institutional buildings with complex histories.

Community Engagement and Urban Impact

Adaptive reuse projects do not occur in isolation. The Oncor Building conversion is part of a larger wave of downtown Fort Worth redevelopment that includes new public plazas, improved transit connections, and streetscape enhancements. The development team has engaged with neighborhood associations, the downtown business improvement district, and city planning staff throughout the design process to ensure the project aligns with broader community goals.

The results speak for themselves. Early lease-up of the residential units has exceeded projections, and the retail spaces have attracted several locally owned businesses that will contribute to the area’s character. For construction professionals, the Oncor Building project demonstrates that adaptive reuse is not merely an environmental choice but a sound business decision that can strengthen urban communities while delivering strong returns.

The Future of Adaptive Reuse in Commercial Construction

As the Oncor Building project moves toward completion, it joins a growing portfolio of adaptive reuse successes that are reshaping how the construction industry thinks about existing buildings. With office vacancy rates expected to remain elevated, the pipeline for office-to-residential conversions will only grow. Construction firms that develop expertise in selective demolition, structural assessment, and phased delivery will be well positioned to capture this emerging market.

The lessons from Fort Worth extend well beyond Texas. Every downtown with mid-century office buildings faces the same question: tear down and start over, or adapt what exists? The Oncor Building provides compelling evidence that with the right team, the right contract, and the right design approach, adaptive reuse can deliver better outcomes on every metric: faster timelines, lower carbon footprints, stronger communities, and superior financial returns. For the construction professionals who master this discipline, the next decade offers extraordinary opportunity.