A Critical Review on Multifunctional Building Envelope Materials for Simultaneous Mitigation of Urban Heat and Noise Islands

Abstract

Rethinking urban models requires resilient designs providing solutions to environmental problems at the building scale. Urban Heat Islands (UHI) and Urban Noise Islands (UNI) often coexist and significantly affect human health and comfort. This article aims to examine dual-function building envelope materials for reducing urban heat and noise islands using the literature review method. Dual-functional building envelope materials provide versatile benefits such as increasing energy efficiency, mitigating environmental challenges in densely populated areas, and improving individual and social health and comfort, in addition to their thermal and acoustic benefits. The use of these materials in building envelopes supports the climate adaptation of cities and provides resource efficiency.High albedo cool materials used for excessive heat reduction can be in the form of cool roofs or cool walls. High reflective materials, cool colored materials, retro-reflective materials, photoluminescent materials, thermochromic materials and sustainable materials are the most common among the cool material alternatives. The use of natural and local white colored gravel of various sizes on cool roofs is a low-cost and efficient approach to UHI reduction. Cool colored materials reflecting the near-infrared part of the solar spectrum bring a suitable solution for historical buildings where white color application is not appropriate. Highly reflective materials combat heat-related risks by reflecting incoming solar radiation directly back to their source due to their special content. Photoluminescent materials, which are still in the research phase, and thermochromic materials that change color when they reach a predetermined temperature are other solutions used to prevent heat-induced problems. Recycled or paraffin, biowaste oil added Phase Change Materials (PCM) also offer environmentally friendly, sustainable solutions for this case. In terms of UNI mitigating techniques, sound absorbing materials with high sound absorption coefficient and low density are widely preferred for building envelopes. Since high albedo materials generally have low sound absorption capacity, although reduction in heat- and noise-related threats is possible separately with the building envelope materials to be selected, multifunctional surface design diminishing both UHI and UNI effects simultaneously still involves various challenges. However, there are various strategies including applications of green walls and green roofs. Innovative approaches such as the use of PCM in pavements or the conversion of noise into green electricity using resonators or acoustic metamaterials also exist. While such solutions have not yet been widely found in practical applications, they are promising for the resilient smart cities of the future. Further experimental validation is needed to evaluate the long-term performance, cost-effectiveness and climate-specific applicability of multifunctional materials.HighlightsMulti functional building envelope materials that simultaneously address UHI and UNI offer great opportunities to create resilient future designs.Using cool materials in building envelopes mitigate UHI related risks.Using sound-absorbing materials in building envelopes mitigate UNI related risks.Innovative solutions such as phase-changing materials and converting harvested noise into electricity are great future opportunities.