R4a 660mm x 1260mm Double Glazed Polycarbonate Dome Only - Opal To Fit Existing or Site Formed Curb of 600mm x 1200mm (External Dimensions) Opal Properties Maintains high light transmission whilst evenly diffusing light area below. Increased security due to translucent finish. 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.