Question

Re. my last question of Heki rooflights, the 2 ventilation options I was after advice on relate to lights with 15cm fixed ventilation and those without. I assume fixed ventilation is something in addition to opening the rooflight itself - so what is it, how does it work, and what are the benefits?

Answer

Rooflights with fixed ventilation are normally installed in caravans and those without fixed ventilation are fitted into motorhomes. The rooflights with fixed ventilation tend to make a 'whistling' noise when the vehicle is moving and therefore are not suitable for motorhomes.
By law the manufacturer has to provide a certain amount of fixed ventilation to allow for the gas appliances that are installed. In caravans some of this fixed ventilation can be provided by the rooflights whereas in motorhomes this ventilation is provided by other means.