S15a 1860mm x 1860mm Double Glazed Polycarbonate Dome Only - Clear To Fit Existing or Site Formed Curb of 1800mm x 1800mm (External Dimensions) Properties Double GlazedLight transmission - 77%.Solar heat gain factor - 69%.Sound reduction (db) - 20.Thermal transmission (w/m2k) - 2.68. Features Polycarbonate rooflights comply with HSG 33 (Health and Safety in Roofwork) recommendations. Patented high security screwbolt fixings. Perimeter seal and screw fixing ensure Em-Dome™ rooflight is fully waterproof. All polycarbonate Em-Domes™ use a minimum 3 mm thick glazing. Acrylic Em-Domes™ have a minimum 3mm outer skin. Inner skin thickness varies according to the dome size. When installed in accordance with the manufacturers' recommendations, Em-Domes™ are expected to exceed the life of the roof covering. Em-Domes™ are guaranteed against the effects of defective design, materials or construction for ten years, subject to certain conditions.