The Gap


All manufacturers recommend that roof windows should be installed into an oversized opening in the roof. This results in a 20mm uninsulated gap around the perimeter of the window.

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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.

97% of roof windows are installed without a proprietary thermal collar

This is because thermal collars are expensive extras which are sold separately.
Keylite is the only manufacturer with an integrated thermal collar which expands to fill the gap. 

At no extra cost.

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.

  • Cold Bridging
  • Condensation
  • Mould growth
*Based on surface condensation check completed to (BSEN ISO 13788), external temperature 0°C, internal temperature 21°C, typical UK Relative Humidity conditions.


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.

  • No Extra
  • Cost Fully Insulated
  • No Condensation