Domed skylights are manufactured using a thermoforming process. The raw material is heated within an oven and when it reaches the correct temperature the polycarbonate is positioned on to a former. It is the former that clamps the edges of the polycarbonate into position and then compressed air blows the dome into its shape. The former also moulds the fixing flange & weather edge too.
A Domed Skylight will be made to the size of the former and this will confirm the Clear Light size and the Overall size too. The Clear light size is normally the amount of light area you will see when you look up at the Domed Skylight when it is fitted on to the roof and the Overall Size is the maximum size the unit will fit to on a pre-made or purchased upstand or builder’s kerb.
If you are looking to replace a Domed Skylight the Measuring guide is as follows;
Please remember that because polycarbonate is a plastic, it will suffer from +/- tolerances of up to 20mm in some cases during the manufacturing process.