If you have an existing gap measure the inner gap, length x width, at all four ends. If there is inconsistency, take the longer measurements. Consult us, if the gap is on a slope.
In case the skylight is not square, you decide the opening side preferably, turning your back to the windier side. The skylight can be mounted directly on the roof.
If the skylight is mounted on a support wall, the support wall must be at least 9 cm thick.
The skylight support should be well finished and smooth.