Building a Cooler City, One Roof at a Time: A Potential Strategy to Mitigate the Urban Heat Island Effect

Overview

Cities are often warmer than nearby rural areas because of the urban heat island effect, where buildings, roads, and rooftops absorb solar radiation during the day and release heat slowly at night. This temperature increase raises demand for air conditioning, increases energy use, and contributes to air pollution. Because rooftops cover a large portion of exposed urban surfaces, the materials used on roofs strongly influence how much heat buildings absorb and how much heat is released into the surrounding air. Material properties such as reflectivity (albedo), thermal conductivity, and thermal mass affect how roofs absorb, store, and transfer heat energy. This project investigated how roof color, material, insulation, and vegetative coverage affect roof surface and indoor temperatures. The hypothesis was that roofing materials with higher reflectivity (higher albedo), lower thermal conductivity, improved insulation (natural or added), or vegetative coverage would maintain lower roof surface and indoor temperatures under direct heating because reflective materials absorb less solar radiation while low thermal conductivity and insulation slow heat transfer into the structure. Identical wooden model houses were constructed and covered with miniature versions of real roofing materials including white and black metal panels, Spanish and grey terracotta tiles, simulated asphalt shingles, and a vegetated green roof. Each roof type was tested with and without foam insulation and placed 35 cm below a heat lamp simulating solar radiation. Roof surface temperatures were measured using an infrared thermometer and indoor temperatures with a digital probe thermometer. Each configuration was tested in three trials and the average temperature change was calculated. Surface temperature measurements showed large differences in heat absorption. Asphalt shingles had the greatest surface temperature increase (about 31–32°C), while white metal and vegetated roofs remained much cooler (about 12–14°C). Without insulation, grey terracotta produced the smallest indoor temperature increase (3.4°C), while black metal and asphalt shingles showed the largest increases (5.4°C and 5.3°C). With insulation, the vegetated roof produced the smallest indoor temperature increase compared with all other roof types. Overall, the results supported the hypothesis that roofs with reflective materials, insulation, and vegetation can reduce heat buildup in buildings and potentially lessen urban heat island effects. Future work could investigate hybrid roof systems combining reflective materials, vegetation, or solar panels to determine whether multiple strategies together yield greater reductions in heat buildup.

Competition history

• CSEF 2026 Materials Science (Junior Division) · Entry J-13-11

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