Perspective Chapter: Prefabricated Building Envelope Modular Assemblies for Secure Facilities

Abstract

Mid-rise and high-rise urban jails are subject to complex performance requirements at the building envelope. This case study examines the design of dual envelope systems—a unitized curtain wall system and a modular steel cell secure perimeter system—for thermal performance and security, emphasizing compliance with the New York City Energy Conservation Code (NYCECC) and ASTM F33 standards. These systems are designed through a design-build, design-assist collaboration with separate subcontractors under contract to the design-builder. Key considerations include the location, spacing, form, and dimensions of structural columns, spandrel beams, or intermediate hollow structural steel supports, and the overall size of unitized curtain wall elements. Additional factors range from the sequence of trades to fire-stopping. The well-being of persons in custody is a primary focus, as the design team aims to create normative environments. Prefabrication plays a crucial role in achieving project objectives. The case study delves into design considerations, the design process, and explores an alternative system approach and its implications.

1. Introduction

In the United States, each county within every state is overseen by a Sheriff responsible for detaining individuals awaiting their first court appearance, except in cases where citation and release apply. According to the 2010 census, there were a total of 50 states and 3143 counties in the United States, which includes the District of Columbia but excludes U.S. territories [1]. However, not every county maintains their own jail facility, leading those without one to house detainees in nearby jurisdictions at a negotiated cost. Nonetheless, jails represent substantial infrastructural investments, especially in highly urbanized areas where land is expensive, necessitating the construction of mid-rise or high-rise jails.

The urgency of addressing climate change has spurred regulatory initiatives aimed at enhancing building performance in many jurisdictions, with the New York City Energy Conservation Code (NYCECC) [2] serving as a pertinent example. This case study focuses on the Borough-Based Jail (BBJ) capital improvement program [3], under which new jails will be constructed in four of New York City’s five boroughs. Each of these boroughs corresponds to a county within the State of New York: Bronx (Bronx County), Brooklyn (Kings County), Manhattan (New York County), and Queens (Queens County) [4]. As per the approved Uniform Land Use Review Procedure (ULURP) for the BBJ program [5], the Bronx and Queens jails are limited to a height of less than 195 feet, while the Brooklyn and Manhattan jails are capped at less than 295 feet [6]. For our purposes, we classify the former as mid-rise and the latter as high-rise structures. The NYCECC mandates rigorous envelope design to mitigate infiltration or exfiltration [7] and thermal bridging, which is critical for both mid-rise and high-rise jail facilities.

Since the cell serves as the innermost security zone within a jail, and BBJ cells are required to provide natural light through a clear glazing area equaling 10% of the room floor area [8], the cell’s exterior wall and glazing must meet or exceed regulatory standards for attack resistance at the secure perimeter. These standards include ASTM F2322-12(2019) Standard Test Methods for Physical Assault on Vertical Fixed Barriers for Detention and Correctional Facilities (60 min) [9], F1592-12(2019) Standard Test Methods for Detention Hollow Metal Vision Systems (60 min) [10], and ASTM F1915-05(2019) Standard Test Methods for Glazing for Detention Facilities (60 min) [11].

This chapter addresses these complex requirements and explores additional factors, such as achieving a weather-tight enclosure promptly, construction trade sequencing, the role of prefabrication in reducing on-site labor and enhancing quality, critical path items related to enclosure within the overall delivery timeline, life cycle cost considerations, carbon footprint, return on investment, construction tolerances, fire-stopping, accommodating building movement, ensuring ongoing maintenance access, the potential for reflective interior surfaces inhibiting vision, and the possibility of a ‘fishbowl’ effect due to the separation of secure and non-secure glazing assemblies, among other considerations. This case study will provide insights into the design-build, design-assist process [12] and the nature of the proposed design. Sustainability is underpinned by the energy efficiency of the proposed design, while an alternative system to a dual systems approach will also be explored, along with its implications.

The final requirement of this case study is that the proposed dual systems or alternative system maintain compatibility with other perimeter conditions within the project and adhere to the Building Exterior Design Guidelines [13]. These guidelines require design-build teams to:

• Design with high-quality, durable, and easily maintained materials that perform optimally over the long term.

• Create functional facades, avoiding the use of decorative elements that serve no function, but instead are performative.

• Consider the use of functional components, such as sunshades or window frames to provide depth and delineate shadow.

• Consider community preferences for a façade design that has layers and fits within the surrounding neighborhood.

• Design the façade to avoid creating lethal illusions for wildlife in transparent or glazed expanses.

Design decisions were reached through a careful balancing act involving concerns for Request for Proposal (RFP) compliance, performance, and cost. Collaboration between the design and construction teams is intrinsic to the design-build project delivery method, and this collaboration intensifies during the in-market procurement phase. In this instance, the procurement takes the form of a design-build competition between two teams, advancing the design to approximately 20% of its development. The stakes are high, as all participants in the design-build competition—even those receiving a stipend when not selected—bear a financial impact if their firms are not selected. Following proposal review and selection of the preferred proposer, a contract is negotiated and registered by the City. Upon receipt of a notice to proceed (NTP), the design-build team begins to implement their proposal, which involves significant additional design alongside actual construction. This case study, however, only addresses the design process that occurred during the in-market procurement period, from RFP receipt to proposal submission.

The in-market period is characterized by highly restricted communication protocols, with the RFP, as amended by addenda, serving as the sole legal basis for generating a proposal. Although feedback sessions with the Program Management Consultant (PMC), the client, and user groups are informative, they are not legally binding. Only the RFP, as amended by addenda, holds legal significance. Design advances iteratively, guided by addenda-driven feedback. Eventually, all requests for information have been submitted and addressed via addenda, and the proposal is submitted by the established due date.

Throughout this process, the first author was a participant (named within the Request for Qualifications (RFQ) response) on one of the competing teams for one of the four BBJ program sites. Thus, he has insights into the design efforts associated with the development of the building envelope conducted by the Architect of Record, the Design Architect, engineering subconsultants on the design team, and contractors and construction managers on the construction team. Recommendations and design decisions were arrived at based on the author’s involvement and consensus-building efforts.

1.1 Research methodology

“Research methodology refers to the principles and procedures of logical thought which are applied to a scientific investigation; a system of methods” ([14], p. 31). The research process should aim to be an integrated, clear, and consistent process that, when rigorously applied, contributes to the advancement of knowledge. Qualitative research explores socially constructed ‘truths,’ emphasizing the complexity of a specific situation. Qualitative research methods include Narrative Research, Ethnographic Research, Grounded Theory, Case Research, Action Research, Interpretative Phenomenological Analysis, and Phenomenological Research. In our context, two of these methods apply: Ethnographic Research and Case Study Research.

1.2 Ethnographic research

Ethnography traces its origins back to the 1700s when researchers began studying social groups and cultures. Researchers typically immerse themselves in the social groups they investigate, actively engaging with subjects and creating detailed assessments from their perspective. Thus, ethnographic research is characterized by a more interpretive and naturalistic approach than traditional research, yielding highly detailed accounts that can range from objective and factual to subjective impressions and explorations of constructed realities [15]. Given the first author’s role, embedded within the design team during the in-market period, the case study research conducted exhibits distinct ethnographic characteristics.

1.3 Case study research

Case study research centers on examining events, individuals, organizations, groups, or change processes. This approach seeks to study the dynamics of a phenomenon leading to specific outcomes. It can incorporate quantitative, qualitative, or mixed methods, adopt inductive or deductive reasoning, and encompass single or multiple cases depending on the research objectives. In our case, a qualitative, inductive, and single-case approach has resulted in outcomes that can be generalized across the BBJ program. These outcomes are generally complex, providing empirical descriptions and defining what transpired, its consequences, and its implications for the future [15, 16]. This process, while limited to the in-market procurement phase, offers insights into the potential application of design-assist during subsequent phases.

1.4 Validation

Validation in qualitative research has been a complex and contested issue for years, with various approaches proposed, but no consensus emergent. At its core, validation aims to ensure the integrity of data collection methods, the collected data itself, and the analytic methods applied to derive outcomes that accurately reflect the data [17]. Alternative terms for internal and external validation, reliability, and objectivity have been proposed, but none have become widely accepted. Definitions of validation span from the broad—“a process of verifying research data, analysis and interpretation to establish their validity/credibility/authenticity” ([15], p. 206)—to the more specific—“an attempt to assess the ‘accuracy’ of the findings as best described by the researcher, the participants, and the readers (or reviewers)” ([18], p. 259).

Creswell and Poth [18] propose several validation strategies and recommend using at least two for study validation. The following validity methods were adopted for this research:

• Addressing researcher bias and reflexivity: the researcher proactively and reflexively addressed any biases, experiences, or factors throughout the study that may have influenced the approaches to, and interpretations of, the design processes and their results captured by the case study [15].

• Triangulation to corroborate evidence: triangulation, defined as using multiple methods or sources of data to confirm the validity of the data, its analysis, or the researcher’s interpretation, was employed [18]. The research was validated via a review by the subject matter expert (SME) second author, resulting in a more comprehensive perspective on the topic.

2. Results and discussion

Performance in the context of building construction can be defined as “the level of service provided by a building material, component or system, in relation to an intended, or expected threshold or quality,” as described by Kesik [19]. Kesik goes on to delineate building envelope performance, including performance requirements and parameters (Table 1), which offer a comprehensive framework for addressing the considerations that our design-build team encountered. This framework will be further augmented with case-specific additions.

Requirement	Parameters
Structural strength/rigidity	Loadbearing/non-loadbearing Wind loading	Seismic loading Thermal effects
Control of heat flow	Effective thermal resistance	Thermal bridging
Control of air flow	Stack and wind pressures Normalized leakage area	HVAC influences Internal partitioning
Control of moisture flow	Rain penetration Vapour diffusion	Air leakage Condensation potential
Control of solar radiation	Opacity/emissivity Solar orientation	Fenestration Shading devices
Control of sound transmission	Airborne sound	Vibration
Control of fire	Fire rating	Combustibility
Durability*	Ultraviolet degradation Corrosion Carbonation Freeze/thaw Abrasion Fatigue Instability/Incompatibility	Biological attack (mould, insects, animals, plants) Chemical attack (soils, contaminants, pollutants) Efflorescence Subflorescence Spalling
Security	Blast protection Ballistic protection	Wind induced Projectile protection
Economy	Initial cost Maintenance cost	Operating cost Life cycle cost
Environmantal impacts	Resource depletion Environmental degradation Reduction of biodiversity	Greenhouse gases Pollutants
Buildability (ease of construction)	Seasonality Tolerances	Coordination Sequencing
Aesthetics	Visual Tactile	Acoustic Olfactory

Table 1.

Contemporary performance requirements and their corresponding assessment parameters [19].

^*

Another aspect of durability related to envelope assemblies is differential durability [19], a term used to describe how useful service life differs—both between components, and within the assemblies and materials comprising components.

2.1 Structural strength/rigidity

The dual systems approach we adopted necessitated the consideration of distinct parameters for the unitized curtain wall system and the internal secure perimeter system. Central to the structural system’s performance are factors such as the location, spacing, form factor, and dimensions of structural columns, spandrel beams, or intermediate hollow structural steel supports, as well as the selected size and span of unitized curtain wall elements. The latter are driven by vertical spans from slab edge to slab edge and can be substantial when floor-to-floor heights are significant, as in the case of two-tier housing, or when outdoor recreation spaces with 18′-0″ clear ceiling heights are required by American Correctional Association (ACA) performance-based standards for jails [20, 21].

The unitized curtain wall system, designed as non-loadbearing, accommodates seismic loading via its slab edge connections while simultaneously isolating the curtain wall from torsional forces. It is also designed to transmit wind loads through these connections and to adapt to expansion or contraction resulting from external temperatures fluctuations.

On the other hand, the internal secure perimeter system comprises steel cells, specifically the loadbearing rear wall of each cell. This wall bears the dead load of the ceiling/roof assembly as well as any other loads imposed on it, including live loads. As steel cells can be stacked, dead and live loads from upper cells are transmitted through the lower cells to the building structure via the structural slab at designated points, resulting in point loads rather than distributed loading. Furthermore, the structural slab must be designed to facilitate the rolling of steel cells into place during construction. Seismic loading is addressed as the steel cell accepts and redistributes applied horizontal forces. The rigid connections between the walls and the ceiling/roof assembly transform each plane of the ‘five-sided box’ into a diaphragm, enhancing the steel cell’s rigidity and ability to disperse horizontal forces. The walls of the steel cells are welded to leveling plates, which, in turn, are welded to embeds in the structural slab at load application points. This rigid connection prevents movement between the steel cell walls and the structural slab. This system remains isolated from wind loads due to structural separation of the dual systems. Thermal effects are negligible since solar radiation is either reflected or absorbed by the unitized curtain wall system, shielding the inner secure perimeter system from most solar heat gain.

As delineated, the structural strength/rigidity parameters from Table 1 manifest differently across the two systems. A similar analysis will be applied to each of the specified parameters.

2.2 Control of heat flow

The unitized curtain wall assembly is, by design, resistant to thermal influences. It consists of two primary elements: the structural frame and the infill panels, including glazed assemblies, glazed spandrel panels, or spandrel panels filled with other opaque finish materials. The structural frame comprises an outer wythe of extruded aluminum, an element providing thermal isolation between the outer and inner wythes, and an inner wythe of extruded aluminum. The temperature of the outer wythe can fluctuate due to external forces such as solar gain, convective cooling, or longwave radiation heat exchange with the night sky. While a temperature differential exists between the outer and inner wythes, and can be extreme, the substantial reduction in thermal bridging inherent in the system effectively mitigates against heat flow in either direction.

2.3 Control of air flow

The dual systems have varying interactions with each other and the internal air volumes within the building. The inner secure perimeter system constitutes a volumetric space, namely the interior of the cell. This air volume is subject to differential pressure compared to adjacent spaces. Within the steel cell, it is essential to maintain eight air changes per hour. This means that new ventilation air is introduced under mechanical pressure, while existing air is displaced through exhaust grilles or leaks in the perimeter of the assembly. Some elements are hermetically sealed, such as the solid metal walls and the pick-resistant sealant between the walls and the floor. Other elements inherently allow air leakage, including the ¾″ undercut of the door, the door perimeter at the jambs and head, and the glazing retention assembly around security glazed openings. Since the dayroom has fewer air changes per hour than the cells, the cells are slightly pressurized, leading to a net air loss to the dayroom. In contrast, the plenum space above, between, and behind the steel cells is not actively ventilated but freely exchanges air with the dayroom and, to a lesser extent, the cell. The physical assembly between the dayroom and the plenum space serves primarily as a security barrier but can also be used as a surface for acoustically absorptive materials, colors, graphics, or murals. It is not designed to resist air flow, resulting in pressure equalization between the dayroom and the plenum. However, the HVAC influences on the modular steel cell secure perimeter system are minor compared to the macro-level impacts on the unitized curtain wall system.

On a larger scale, mid- and high-rise buildings are influenced by the stack effect, a significant driver of air flow. This effect must be resisted by the unitized curtain wall system. Additionally, this system must contend with (positive) wind pressure or negative air pressure created by wind vortexes. Air infiltration or exfiltration is a major contributor to energy loss or gain, affecting heating and cooling loads and overall energy efficiency.

The interface between the systems is black EMSEAL QuietJoint^® SSH, which is non-invasively anchored to the steel cell and mechanically compressed against the mullions of the unitized curtain wall system when the steel cells are positioned. A butted, non-sealed approach to the joints mitigates glare and dust infiltration and allows potential condensation to disperse within the pressure-equalized plenum while Brownian motion efficiently dissipates heat buildup. Reductions in glare due to the absorptive black interface mitigate the ‘fishbowl’ effect, offering a more normalized experience of looking through two layers of glazing for persons in custody.

2.4 Control of moisture flow

The parameters for moisture flow, including rain penetration, air leakage, vapor diffusion, and the potential for condensation, all apply to the unitized curtain wall system. The HVAC system regulates interior air temperature and humidity while introducing fresh air and exhausting air at a similar rate. The inner secure perimeter system is surrounded by dayroom air, both within the dayroom and the plenum space over, between, and behind it. This isolation shields the inner secure perimeter system from humidity fluctuations, given the similar levels of humidity and temperature in the introduced ventilation air.

Conversely, the unitized curtain wall system serves as a mediator between the plenum’s temperature, humidity, and pressure and exterior atmospheric conditions. Pressure differentials, humidity differentials, and levels of air leakage through this system challenge its performance. Perfect building envelopes are elusive, as they would be costly and maintenance intensive. They would lack the redundancy of critical control functions and would not drain water were it to penetrate. Therefore, our proposed pressure-equalized rain screen design for the unitized curtain wall system aims to eliminate most wind-driven, rain-based infiltration; pressure differential-induced or air leakage-driven vapor diffusion; and capillary action through the system.

2.5 Control of solar radiation

The unitized curtain wall system’s glazed panels consist of 1″ nominal insulated glazing units (IGU), often referred to as air gap units, featuring a low-e coating on the #2 surface that blocks 62% of solar energy while allowing 70% of visible light to pass through. When light interacts with any glass surface, some is transmitted, some is absorbed, and some is reflected. This phenomenon extends to the inner pane of the air gap unit, where an additional 13% of solar energy is reflected or absorbed. In aggregate, only 33% of the original potential solar heat gain contributes to heating the plenum air or the exterior surfaces of the inner secure perimeter system’s rear wall. The security glazing within this wall is glass-clad polycarbonate (GCP) with a nominal 1″ thickness and a shading coefficient of .80, mitigating solar gain even further. Fritting is also applied to the IGU to meet bird safety requirements outlined in the Building Exterior Design Guidelines [13] and in more detail by the New York City Buildings Department [22].

A significant challenge of the dual systems approach lies in managing the solar gain-related heat buildup within or between the glazed assemblies of each system. Even with a low-e coating that mitigates a substantial portion of solar heat gain, some still passes through the outer IGU. Since the two wythes of the unitized curtain wall are joined by thermoset, a reinforced composite thermal break material that mitigates thermal wicking effectively, dissipation of unwanted heat must still be careful considered.

One concern arises at the glass laminate interlayer and the polyisobutylene (PIB) air spacer at the perimeter of an IGU. Manufacturers generally do not warrant their products above temperatures of approximately 80°C (176°F), with some extending to 100°C (212°F). Careful detailing of the assembly must facilitate venting of the sealed cavity while managing dirt and dust infiltration. Proposed designs should be analyzed using thermal simulation software, predicting temperatures through transient or steady-state analysis to ensure continued performance of all components.

Unitized curtain wall system spandrel panels, irrespective of material, are opaque and insulated, effectively controlling solar radiation. While solar orientation and shading are vital considerations, we will assume an orientation equal to the median condition for the purposes of this generalized case study. We will also assume that shading devices are absent from the design.

2.6 Control of sound transmission

Sound transmission through the building envelope is a crucial aspect of design. The unitized curtain wall system is intentionally designed to mitigate environmental noise, considering the materials used for both its spandrel and glazed panels. The glazed panels are detailed as nominal 1″ IGUs with a Sound Transmission Class (STC) rating of 35. Additionally, the 4″ air gap between the systems contributes a STC of 6, and the GCP provides a STC of 27 for each 0.25″ pane of heat-strengthened or chemically strengthened glass and a STC of 34 for the ½″ monolithic polycarbonate core. The use of interlayers to bind these three layers further enhances performance. While the newer Outdoor/Indoor Transmission Class (OITC) rating system would provide a better estimate of sound attenuation through exterior wall assemblies, limited manufacturer testing restricts the use of this rating system.

In essence, the dual systems effectively attenuate sound and noise, even at their weakest point. While structure-borne vibration remains a possibility, specific measures to mitigate it will be determined as the design progresses beyond the in-market period for the BBJ.

2.7 Control of fire

The materials in the dual systems, such as aluminum, glass, open-cell foam with a fire-resistant, acrylic-based mass-loading agent, steel, and GCP, are generally non-combustible, except under extreme fire conditions. Several measures are in place to prevent such conditions from occurring. Firestopping at the slab edge isolates each floor, eliminating the vertical spread of fire via the stack effect. Each floor is subdivided into smoke zones, contributing to fire fighting and enabling the protect-in-place life safety paradigm typical in jails under I-3 conditions. Further elaboration on this parameter is unnecessary.

2.8 Durability

The durability parameters outlined in Table 1 are largely mitigated or eliminated due to the design and materiality of the unitized curtain wall system. Less sophisticated curtain wall systems have evinced an effective design life of 50 years or more. Given more than 50 years of technological advancement and lessons learned, it is reasonable to assume a longer design life for this system.

For the inner secure perimeter, the materiality and construction of the steel cells are designed to mitigate intentional attempts to defeat or degrade their performance as a security barrier. Interior surfaces can be refurbished if vandalized or degraded, and if GCP is damaged, it is inside glazed to facilitate replacement.

2.9 Security

The BBJs are secure facilities, intrinsically able to mitigate blast effects, wind-driven projectile impacts, and bullet penetration due to their design and materiality. Even though these parameters were not the primary design focus of the dual systems comprising the building envelope, they result from the attack resistant design.

Designers will continue to explore the performance of these designs as they are further developed post-selection.

2.10 Economy

Constructing the proposed dual systems is a significant investment, and these buildings are expected to be very expensive. In addition to their design, factors such as the global COVID-19 pandemic, supply chain disruptions, labor availability issues, and other externalities continue to impact costs and lead times. The design-build method used for project delivery aims to mitigate initial costs by enhancing efficiencies in design and construction coordination and informs approaches to schedule mitigation. These systems contribute significantly.

Operating costs, including utility costs, are expected to benefit from the high-performance envelope’s reductions in heating and cooling loads. However, ongoing building maintenance and fine-tuning of complex interdependent systems through Building Management System monitoring and adjustment are essential to optimizing building operations and reducing overall life cycle costs over the extended life of these mission critical 24/7/365 buildings.

2.11 Environmental impacts

The scale and intensive use of these buildings will result in a significant carbon footprint. Additionally, the rated capacity of the BBJ system is constrained, and systemwide pressures are likely to require operating at or near the rated capacity throughout their design life, even with potential additional rated capacity being added to the jail system in response to population growth.

Constructed on city-owned sites within urban areas, these buildings are not expected to contribute to a reduction in biodiversity. In fact, their construction is anticipated to enhance the streetscape through thoughtful landscape design that improves upon existing uses and environments at these sites.

While several of the materials used contribute to significant carbon footprints, their durability and maintainability as well as the buildings’ extreme design life of a minimum of 80 years or, given their historic precedent Rikers Island, potentially more than a century of continuous use will amortize these environmental costs over an extended timeframe. Typical institutional buildings of the same scale with more typical design lives contribute to cyclical demolition and replacement over the same timeframe at much higher cost to the environment.

2.12 Buildability (ease of construction)

These dual systems represent the most complex prefabricated assemblies in the project(s). Both are prefabricated to the greatest extent possible and erected on-site to enhance construction efficiency and reduce the intensity of and need for onsite labor at prevailing wages as required by the Project Labor Agreement (PLA). Sequencing of trades, reductions in mobilization time, and reductions in general conditions and schedule duration are achievable through this approach. Prefabrication increases quality by ensuring factory-controlled conditions and assembly repetition. Construction tolerances are meticulously addressed through detailing that mitigates potential issues. Additionally, prefabrication accelerates “drying-in” via the rapid erection of the unitized curtain wall system, which allows earlier installation of finishes, accelerating the overall schedule.

2.13 Esthetics

The Building Exterior Design Guidelines [13] emphasize esthetics within the context of performative suitability within neighborhood contexts. However, the inclusion of Public Design Commission (PDC) review [23] in the overall process centralizes esthetic considerations and represents a series of significant hurdles to implementation. This multistage public process often involves substantial revisions to the proposed design at each stage. Esthetics thereby become critical not only for being selected as the preferred proposer, but also for successful implementation by the four contracted design-build teams.

3. Alternative systems and their implications

The most apparent alternative to the dual systems approach is to consolidate the performance requirements of both systems into a single-skinned system. This would require a unitized curtain wall design capable of meeting all envisioned performance requirements, including the energy performance mandated by the NYCECC, while simultaneously meeting or exceeding the forced entry standards for the secure perimeter of a jail.

Such a system would require several key characteristics:

In terms of the framing system, it would have to be constructed from aluminum-clad steel and be thermally broken. Although U.S. manufacturers already offer such systems for punched openings, adapting this concept to a curtain wall is a significant and challenging leap.

Regarding the glazing system, the glazing assemblies would need to replicate those used in the dual systems examined in this case study. The external IGU would address thermal, solar, wildlife, and weather concerns, while the inboard security glazing would provide vandalism and attack resistance. These two assemblies would be retained by a system-spanning framing system, creating an air-filled cavity between them, which would be factory-sealed and carefully vented to avoid heat buildup. The inboard security glazing assembly and associated framing would anchor to available structural substrates. The unitized system would be pre-glazed in the factory for delivery but allow replacement of the glazing from both sides.

Considering structural design, the system would need to account for the maximum span between structural supports, likely requiring the inclusion of Hollow Structural Steel (HSS) columns between the ceiling/floor assemblies that the unitized curtain wall system vertically spans. The design of the curtain wall anchor system, which ties the loads from the curtain wall back to primary structure, is of particular concern. It would involve tying the steel inner wythe of the frame to the slab with steel elements, which is not commonplace in the curtain wall industry. These anchors, along with the fire-safing-filled slab edge gap, must remain inaccessible to persons in custody and other building users. This would necessitate detailing that will mitigate thermal bridging while preserving constructability and erection speed.

As for testing, the notional single-skinned system would require rigorous laboratory testing to all relevant performance criteria. Each type of test necessitates the provision of an assembly, making testing expensive and time-consuming due to the limited number of testing laboratories. This adds to both cost and scheduling delays.

Despite the desirability of such a single-skinned system in an increasing number of urban jails, it is unlikely to materialize in time for the BBJ program. The program’s delivery method and legislatively mandated schedule will make it challenging to accommodate this innovation [24].

4. Conclusion

The dual systems proposed in this design-build case study offers several advantages. They expedite the achievement of a weather-tight enclosure, improve the sequencing of trades, leverage prefabrication to reduce on-site labor and enhance quality, and decouple enclosure-related critical path items from the overall delivery timeline. They embody the best outcomes of a design-build, design-assist process given the technologies currently available.

Furthermore, these dual systems ensure that all the City’s requirements, including sustainability supported by the energy efficiency of the proposed design over its lengthy anticipated design life, will be met or exceeded. This is achieved through inspired coordination and integration both within and external to the design-build team, based on the level of design completed during the in-market phase of procurement.

Acknowledgments

Ellyn A. Lester, Ph.D. of Pennsylvania College of Technology, Williamsport, PA, USA, provided methodological guidance.