The challenge of a flat roof is to balance durability and strength with weight. Concrete slab roofs are often used for flat rooftops, but this may not be an ideal solution in buildings which cannot support the heavy weight of poured concrete.
The best solution is to use a hunk of concrete with Expanded Clay Aggregate (ECA.) ECA has a number of properties which make it ideal for flat rooftops. It has a very low thermal conductivity coefficient, sound-insulating properties, and is moisture-impermeable. In addition, it’s extremely lightweight while maintaining strength and incompressibility. It also reduces earth pressure and overall building weight.