Singapore's tropical climate has long presented challenges for residents, but a groundbreaking collaborative study involving the National University of Singapore (NUS) has brought to light a pressing issue: heat trapped inside homes due to inadequate ventilation. This research, part of the broader Cooling Singapore 2.0 initiative, reveals how everyday factors in Housing and Development Board (HDB) flats exacerbate indoor temperatures, leading to significant health risks. Conducted across diverse neighborhoods, the findings underscore the urgent need for improved airflow strategies in densely built urban environments.

The study highlights that nearly half of the 416 surveyed HDB flats recorded higher indoor heat indices than outdoor conditions, with some reaching up to 5°C warmer than nearby void decks. This phenomenon, driven by poor air circulation, affects sleep, daily activities, and overall well-being, particularly among vulnerable groups like seniors and low-income families. As Singapore grapples with rising urban heat island effects, universities like NUS are at the forefront, pioneering solutions that blend engineering, medicine, and urban planning.

Unveiling the Scope and Methodology of the NUS-Led Research

The research emerged from the Climate Resilient Citizenry project, spearheaded by the Singapore University of Technology and Design (SUTD) in partnership with NUS Yong Loo Lin School of Medicine, the Singapore-ETH Centre, and Singapore Management University (SMU). Over nine months starting October 2024, teams visited 416 HDB flats spanning nearly all flat types—from compact one-room rentals to spacious executive units—across 10 neighborhoods. More than 1,000 residents participated in surveys detailing their heat experiences, coping mechanisms, and home layouts.

Researchers employed heat index measurements, which factor in temperature and humidity to gauge perceived heat stress, alongside airflow assessments using anemometers. Indoor clutter levels were quantified, window usage patterns documented, and resident behaviors analyzed through questionnaires. This holistic approach provided unprecedented insights into real-world home environments, moving beyond simulations to on-site data collection. Associate Professor Jason Lee from NUS Medicine, a co-leader, emphasized the study's novelty: "This is the first time researchers have entered homes to quantify urban heat's impact on daily life."

The methodology's rigor, combining quantitative sensors with qualitative surveys, sets a benchmark for urban climate research in tropical cities. NUS's involvement brought physiological expertise, linking environmental data to human health responses.

Key Findings: Indoor Temperatures Exceeding Outdoor Levels

Central to the study was the discovery that approximately 50% of homes were warmer indoors than outdoors, defying the expectation that residences serve as cool refuges. One-third showed differences of up to 2°C compared to void decks, while 10% exceeded 5°C. In extreme cases, indoor heat indices hit 36.2°C against 27.8°C outside, creating sauna-like conditions.

Airflow was critically low in 60% of homes, with stagnant air trapping heat from concrete surfaces, appliances, and cooking. Dr. Harvey Neo from SUTD noted, "Higher clutter and prolonged closed windows correlate directly with warmer, stuffier interiors." These patterns persisted across flat generations, though older units with poorer natural ventilation fared worse.

Nearly 60% of residents reported disrupted sleep and outdoor activities as primary victims, with work productivity and social interactions also suffering. This data paints a picture of pervasive, normalized discomfort in Singapore's public housing, where over 80% of the population resides.

Factors Trapping Heat: From Clutter to Urban Design

Poor air circulation stems from multiple interconnected factors. Indoor clutter—furniture, partitions, and stored items—blocks airflow pathways, preventing cross-ventilation essential in Singapore's humid climate. Keeping windows closed for privacy, noise reduction, insect control, or security further exacerbates stagnation.

Home layouts play a role; long corridors and inward-facing rooms limit breeze penetration. Building clusters impede external winds, while heat-emitting sources like refrigerators and stoves add internal loads. Concrete's thermal mass retains daytime heat, releasing it nocturnally. Dr. Samuel Chng from SMU highlighted behavioral normalization: "Residents endure heat as 'normal,' delaying interventions until peaks."

These insights align with NUS's urban heat island research, where compact high-rises amplify temperatures by 4.3°C over open areas. Retrofitting older HDB blocks could mitigate this through strategic openings and shading.

Health Implications: Beyond Discomfort to Chronic Risks

The study's health focus, led by NUS Medicine, reveals indoor heat's insidious effects. Prolonged exposure causes cumulative physiological stress, impairing thermoregulation, especially in seniors whose capacity wanes with age. Sleep fragmentation reduces restorative deep sleep, heightening cardiovascular risks, cognitive decline, and mental health issues.

Vulnerable groups—elderly, low-income in smaller rentals—face compounded threats, with limited AC access. Assoc Prof Jason Lee warned, "Seniors, accustomed to no AC, under-recognize stress, delaying cooling." Heat also worsens dehydration, heatstroke susceptibility, and vector-borne diseases via stagnant air.

Project HEATS, NUS-led, complements this by quantifying heat's toll on sleep and activity. Wearables tracked skin temperature and heart rate, showing poor ventilation correlates with fragmented rest. Long-term, this burdens Singapore's healthcare, emphasizing preventive urban design.Straits Times coverage

Resident Coping Mechanisms and Voucher Utilization

Surveys showed 76% rely on fans, followed by window opening and light clothing. Nighttime AC use exceeds daytime (over 50% vs. 14%), prioritizing sleep. However, $300 climate vouchers saw 60% non-use; high AC costs deterred purchases despite awareness.

Low-income households favor passive methods, normalizing discomfort. This resilience masks risks, as Dr. Chng observed: "Mindset of endurance turns dangerous amid climate change." Education on heat thresholds is key.

Singapore Universities Driving Heat Resilience Research

NUS, SUTD, SMU exemplify collaborative higher education tackling national challenges. NUS's Heat Resilience & Performance Centre pioneers physiological studies, while SUTD models ventilation via digital twins. Cooling Singapore 2.0 integrates these for policy impact.

Such interdisciplinary work trains future experts in sustainable urbanism, climate health. NUS's role positions it as leader, fostering careers in environmental engineering, public health.

Projects like HEATS develop smart cooling—dynamic AC, wearables—translating research to homes. Universities bridge academia-industry, advising HDB on retrofits.

Practical Recommendations for Cooler Homes

Experts urge decluttering for airflow, cross-fans (one exhausting hot air), solar films on sun-facing windows. Modeling tools simulate layouts, factoring real behaviors like partial window opening.

Policy: Co-fund AC for vulnerables, ventilation-focused renovations in aging HDB. Dr. Zheng Kai (SUTD) stresses realistic simulations: "Guidelines assume full openings; reality includes rain, bugs." Prof. Petra Tschakert (NUS) adds: "Barriers are infrastructural, not awareness."SUTD project page

Broader Implications for Singapore's Urban Future

As temperatures rise 1.5-4°C by 2100, indoor heat threatens productivity, healthcare costs. Universities advocate systemic changes: green roofs, district cooling, resilient designs. NUS's urban heat pillar integrates data for city-scale solutions.

Vulnerable focus—seniors (25% population by 2030)—demands equity. Research informs Green Plan 2030, positioning Singapore as tropical heat model.

Future Research and Innovations from NUS and Partners

Ongoing: HEATS tests bedroom interventions; DUCT builds climate twins predicting heat. AI optimizes ventilation, wearables nudge behaviors. Universities eye scalable tech for HDB upgrades.

Careers bloom in climate resilience—roles in research, policy, engineering. NUS/SUTD grads lead Singapore's heat-proofing.

Actionable Insights for Residents and Policymakers

• Declutter floors, use exhaust fans post-cooking.
• Install solar films, timers on AC.
• Claim vouchers strategically; seek subsidies.
• Advocate retrofits via town councils.

This NUS-centric collaboration empowers change, safeguarding health amid urbanization.

Photo by Joshua Kettle on Unsplash