Over the past several decades, buildings have become remarkably good at conserving energy. Walls became better insulated, HVAC systems became more efficient, and building envelopes became tighter and more sophisticated. Across the construction and design industries, energy performance became one of the defining measures of a successful building. In many respects, those efforts worked exactly as intended. Modern buildings consume less energy and perform better thermally than the structures built a generation ago. At the same time, many of those same buildings gradually became darker places to live, learn, and work as architects and developers responded to increasingly stringent efficiency requirements.
This spring, the International Code Council advanced new daylighting proposals that would require greater access to natural light in classrooms, apartments, dormitories, and hotels during its latest public comment hearings in Hartford, Connecticut. According to the National Glass Association, the proposals are intended to modernize code requirements around occupant wellbeing, daylighting, and building performance. While these proposals may initially appear narrow in scope, they reflect a much larger shift happening across architecture, urban planning, and building policy. The industry is beginning to reconsider what building performance actually means and whether energy efficiency alone is an adequate measure of a healthy indoor environment.
How Buildings Became Darker
For years, sustainable construction focused heavily on metrics that were relatively straightforward to quantify. Architects, engineers, and policymakers measured heat loss, operational efficiency, air leakage, and energy consumption with increasing precision. Within that framework, windows were often viewed as a challenge because conventional glazing represented one of the weakest thermal components in the building envelope.
As energy codes became stricter, developers and designers responded rationally to the incentives placed in front of them. Window areas shrank in many projects. Floorplates deepened to maximize usable square footage. Artificial lighting became increasingly central to how interior spaces were designed and occupied. Buildings were optimized around energy conservation, and in the process, natural light gradually became less important within the broader hierarchy of design priorities.
The consequences of those decisions are now visible in many cities. Apartment units rely on borrowed light from adjacent rooms. Offices extend deep into artificially illuminated interiors. Students spend long school days in classrooms with limited daylight exposure. In the pursuit of efficiency and density, access to natural light often became secondary to thermal performance and rentable square footage. Many of these changes occurred slowly enough that they were accepted as a normal part of modern urban development rather than as a meaningful shift in the human experience of indoor environments.
Why the ICC Proposals Matter
The new ICC daylighting proposals suggest the industry may be starting to reconsider that trajectory. One proposal focuses on classrooms and educational facilities, while another addresses residential occupancies such as apartments, dormitories, and hotels. Together, they represent a growing recognition that natural light is not simply an aesthetic feature or architectural luxury. It plays a meaningful role in how people experience indoor environments every day.
The significance of these proposals extends beyond the specific requirements themselves. The National Glass Association, working alongside the American Institute of Architects, the Glazing Industry Code Committee, and researchers including Professor Juan Miro of the University of Texas at Austin, supported the measures throughout the ICC hearing process. The proposals emerged partly in response to growing concern around windowless dormitories and other habitable spaces with limited access to natural light. More information about the proposals and hearing outcomes is available through the National Glass Association’s ICC coverage.
This shift did not emerge in isolation. Over the last several years, discussions around healthy buildings have expanded considerably. Employers increasingly market workplaces around wellness and occupant experience. Universities emphasize student wellbeing in new campus developments. Healthcare facilities, recreation centers, and commercial projects now routinely discuss indoor environmental quality alongside sustainability goals. Across sectors, there is growing recognition that people experience buildings psychologically and physiologically, not simply functionally.
Research connecting daylight exposure to cognitive performance, circadian rhythm regulation, concentration, and mental wellbeing has also become increasingly difficult to ignore. Buildings shape human behavior and physiological experience far more than the industry historically acknowledged. Most people now spend the overwhelming majority of their lives indoors, yet many indoor environments are still designed primarily around mechanical performance rather than the human experience of occupying those spaces over long periods of time.
The Expanding Definition of Building Performance
The daylighting proposals also arrive during a broader evolution in building policy discussions surrounding the 2027 International Energy Conservation Code cycle. The ongoing 2024-2027 ICC development process has expanded conversations around resilience, electrification, embodied carbon, passive performance, and broader building outcomes as industry groups continue shaping the next generation of model codes. Additional information about the ongoing hearings and code-development process is available through the International Code Council.
Importantly, this does not mean energy efficiency is becoming less important. Reducing energy consumption remains essential as cities confront rising energy demand and climate pressures. What is changing is the understanding that operational efficiency alone may not fully define a successful building. The conversation is expanding toward a more balanced view of performance that also considers the long-term experience of the people inside these environments.
That philosophical shift matters because the built environment shapes nearly every aspect of daily life. Buildings influence mood, productivity, fatigue, focus, and overall comfort in ways that are often subtle but cumulative over time. As the industry continues to refine how performance is measured, indoor environmental quality is increasingly becoming part of the discussion rather than an afterthought. The ICC daylighting proposals represent one of the clearest signals yet that regulators and industry leaders are beginning to think more broadly about the relationship between sustainability and human wellbeing.
The Challenge of Office-to-Residential Conversion
This conversation becomes especially important as cities accelerate office-to-residential conversion projects. Across North America, municipalities are looking at underused office towers as a potential solution to housing shortages and downtown revitalization. The adaptive reuse movement has gained momentum because it offers cities a way to add housing supply while repurposing existing infrastructure.
Many of these office buildings, however, were never designed to support residential-quality daylight access. Large office floorplates were built around assumptions of artificial lighting, temporary occupancy, and centralized mechanical systems. Deep interior spaces that functioned adequately for commercial work environments can become much more problematic when converted into homes where people spend most of their personal lives. Residential environments require a different relationship with daylight because they shape routines tied to sleep, concentration, mental wellbeing, and long-term comfort.
This creates a difficult design challenge for architects, developers, and policymakers. Cities understandably want to increase housing density and accelerate conversions, but indoor quality cannot become secondary in the process. If future residential development focuses exclusively on supply and speed, many urban environments may struggle with long-term livability concerns related to daylight access, comfort, and overall occupant well-being.
The growing focus on daylighting reflects a larger realization that dense urban living must also remain humane and psychologically sustainable. The future of successful cities will depend not only on how many housing units they create, but also on the quality of the environments people inhabit within those spaces every day. The questions raised by the ICC proposals are therefore likely to extend far beyond classrooms and residential occupancies over time as policymakers and designers continue to reconsider what healthy buildings should provide to the people inside them.
A Different Vision of Sustainable Architecture
The significance of the ICC daylighting proposals ultimately extends far beyond windows themselves. They suggest the building industry may be entering a period where energy efficiency alone is no longer the defining measure of success. Sustainable buildings should conserve energy, but they should also support concentration, comfort, wellbeing, and quality of life.
For decades, the industry optimized buildings around what it could most easily measure. The next phase of architecture may involve a broader understanding of performance that places greater emphasis on the human experience indoors. As building standards continue to evolve, the most successful environments may ultimately be those that balance sustainability with the everyday realities of how people live, learn, work, and feel inside the spaces surrounding them.
