Architect A. William Hajjar (1917–2000) was obsessed with two seemingly contradictory architectural concepts: the square-plan building and environmental design. A square-plan building is often designed in a three-by-three, four-by-four, or other double-symmetrical grid with the same façade appearance to all its sides, thus being unspecific in orientation. Environmental design, on the other hand, responds to local site conditions and orientation-specific solar and wind patterns. As archival studies revealed, in the late 1950s, Hajjar developed a façade system that allowed him to negotiate these two concepts. Called “Air Wall,” it surrounded an entire building and consisted of two glass-curtain walls approximately three feet apart. Within the two glass layers, air moved freely between cold and warm orientations to create a temperature equilibrium surrounding the occupiable space. In various square-plan designs, Hajjar explored different grids and transformed the Air Wall for local climates. For the temperate conditions of Pennsylvania, it was intended to create a warm “air blanket” on cold days, with operable vents removing heat on hot days. A three-story test structure was built in 1959 on the campus of Pennsylvania State University to investigate the functionality of the Air Wall concept. For a 1965-municipal office building in the warm-humid climate of coastal Virginia, designed by architect Vincent G. Kling (1916-2013), Hajjar’s Air Wall research was adapted by utilizing heat-absorbing tinted glass for the outer glass layer with openings on every floor to improve ventilation. Discussing selected projects by Hajjar, the paper unpacks the architect’s strategies to negotiate the square plan with environmental design. It thus contributes to understanding the conflicting mid-century architectural discourses and to reconciling two seemingly contradicting concepts, both universally used and contextually adapted in today’s design tasks.

The paper examines how contemporary multifamily housing—understood as both spatial typology and cultural artifact—might be recalibrated toward a more nuanced, threshold-based framework. Amid a global housing crisis and widening socio-spatial inequities, value-engineered inward-facing typologies prioritize oversized private interiors while minimizing gradated thresholds between domestic and civic realms. The result is a spatial regime that exacerbates isolation, demographic stratification, and diminished social resilience. In response, the paper introduces the threshold spectrum as both a theoretical framework and an operational design instrument. Drawing from Space Syntax research and global precedents, the spectrum identifies a layered sequence of inhabitable spaces (the domestic hinge, cluster commons, and civic ground) through which adjacency, permeability, and shared infrastructure shape everyday life. Thresholds are understood not as residual spaces, but as essential spatial infrastructure that sustains dwelling. The framework is tested through an applied spatial study, the Commonscape project, sited within Charleston, South Carolina’s historically regulated and climate-vulnerable urban fabric. By elevating residential clusters above permeable civic ground and externalizing circulation as inhabited gallery space, the project demonstrates how threshold-rich configurations can reconcile preservation constraints, environmental risk, and long-term housing needs. Rather than proposing a singular formal solution, the paper advances a scalable spatial ethic – one that reframes housing as an ecology of interdependent thresholds and positions social viability as a core metric of design.

In the context of accelerating climate change, operational historic buildings, particularly in hot arid regions, face increasing thermal discomfort and rising energy demands. As many remain in daily use, retrofitting presents a complex challenge. Interventions must improve comfort and efficiency while preserving architectural integrity and complying with heritage conservation guidelines. This paper presents a primarily digital simulation-based and partly observational methodology for climate adaptive retrofitting through low-impact, phased interventions that enhance thermal comfort and reduce energy use intensity over time.

The study focuses on a historic house currently used as office space on the University of Arizona campus in Tucson, AZ, USA. Following one month of on-site observation and indoor environmental monitoring, including temperature and humidity measurements, a digital twin of the building was developed and segmented into 29 functional zones. Using Rhino and Grasshopper with Ladybug, Honeybee, and “OpenStudio”, the model evaluated projected climate conditions based on NOAA 1991–2020 Climate Normals, extended in 30-year intervals for 2020, 2050, and 2080. Eight retrofit scenarios were defined across minimal, moderate, and extensive resource tiers and aligned with building lifecycle maintenance phases. Design strategies included attic and wall insulation, operable glazing systems, aperture shading, and user-engaged passive interventions. Each scenario was assessed using energy use intensity metrics and thermal comfort thresholds defined by the ASHRAE 55 adaptive comfort model.

Results show that moderate-level interventions, including attic insulation, operable double-pane windows, and operable shading systems, achieve the best balance between energy reduction and occupant comfort. These strategies reduced energy use intensity to approximately 70 percent of baseline while maintaining adaptive comfort compliance in primary occupied zones. The framework supports scalable, evidence-based decision-making by linking simulation feedback with resource availability and maintenance cycles, emphasizing adaptability and incremental implementation within preservation constraints.