Why isn't double glazing used in the Gulf to keep the heat out, in combination with reflectionfoils? Investment costs? what are the long term effects?

Climate responsive design and traditional design elements of the Persian Gulf may provide a basis for low-energy design. Current building models employed in the United Arab Emirates are often unsuited to the region’s climate, causing massive cooling loads as a result of inappropriate site planning, orientation and building envelopes with high levels of glazing. The application of an inter-disciplinary design approach that considers urban design, landscape design, architecture and meteorology may provide a more appropriate low-energy design for such hot and arid climate.

Double glazing in combination with reflection foils definitely would help along with adopting the latest designs and technologies of energy conservation and HVAC specially.