Condensation

In areas or buildings likely to suffer heavy condensation, the use of a second translucent sheet to form a double skin can be used to minimise condensation. See Types Of Roof Lights.

Twin skin plastic sheeting should have a minimum gap of 20 mm and should be spaced with insulating material between the sheets at the fixing points. It is standard practice to place the second sheet above the first after it has been fixed; however, a special ridge is required as shown on Sprung Roof.

Elevated roof lights, designed specifically for long run tray roofs from ridge to eaves, are fixed to the ribs of the sheet and permit condensation to run off onto the trough.

A UV stabilized grade of clear polythene film or sheeting can also be used in order to help control any condensation dripping from the plastic roof lighting, but its durability may be less than that of the plastic roof sheeting.