Obviously this gap needs to be insulated. Other manufacturers will sell you a separate Thermal Collar to insulate this gap (very few people actually purchase a separate thermal collar).
New building regulations are, for the first time, legislating for the cold bridging implications of roof windows. Thermal values (Psi) around the roof windows must now be considered.
Improvements to the overall air tightness and thermal performance of a home may lead to condensation problems unless careful design and construction practices are adopted.
Keylite guarantee to insulate the gap.
When left un-insulated, the gap in the roof allows a cold bridge through the frame, cooling the internal surface to below dew point temperature.*
This causes condensation to form on the frame which can run off onto surrounding surfaces with the risk of mould growth.
Only with Keylite do you get an Integral Thermal Collar that expands to fill and insulate this gap.
Other manufacturers will sell you a separate thermal collar to insulate this gap (Very few people actually purchase a separate thermal collar) and your installer may fail to insulate this gap.