The short answer is: yes, it very likely can. On a shadeless rooftop, plastic urban outdoor furniture is subjected to intense, direct sunlight and extreme heat, which are primary causes of warping, fading, and weakening. Not all plastics are equal, however. Inexpensive, hollow polypropylene or HDPE furniture is highly susceptible to deforming under high temperatures. More durable options like high-density polyethylene (HDPE) lumber or polyvinyl chloride (PVC) resin furniture are formulated to be more UV-stable and heat-resistant, but prolonged exposure still takes a toll.
To minimize warping, choose furniture specifically labeled as UV-protected and heat-resistant. Light colors reflect more heat than dark ones. Use protective covers when the furniture is not in use, and consider lightweight, breathable shades to reduce direct exposure. Regularly clean with mild soap and water to prevent dirt from trapping heat on the surface. While no plastic is entirely immune, selecting the right materials and providing basic care can significantly extend the life and appearance of your rooftop furnishings.