C4 860mm Double Glazed Polycarbonate Circular Dome Only - Clear To Fit Existing or Site Formed Circular Curb of 800mm (External Dimensions) Properties Double Glazed:Light transmission - 77%.Solar heat gain factor - 69%.Sound reduction (db) - 20.Thermal transmission (w/m2k) - 2.68.Triple Glazed:Light transmission - 70%.Solar heat gain factor - 60%.Sound reduction (db) - 22.Thermal transmission (w/m2k) - 1.78. 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.