The room will be colder more glass means more heat loss.
Roof lantern heat loss.
Well the principle of rooflight design means that a rooflight can potentially lose 35 to 45 per cent more heat during cold weather spells than a similar window installed on the side of a house.
Heat loss of course incorporating a roof lantern to your extension will result in more heat loss than just a flat roof the same as putting windows in a room does.
Modern glazing has seen radical improvements and started to shake this historic view which is also the case with the roof lantern.
Combined with high performance glazing our aluminium roof lanterns can achieve u values as low as 1 0 w m2k.
The aluminium frame is designed to be as energy efficient as possible with an insulating t bar and thermally broken eaves beam.
Including a roof lantern opens up the room and gives a feeling of space.
If you re thinking of having 4m bifolds plus a roof lantern your kitchen will be so cold you could never use it.
Convection the draft loop.
I seriously suggest you reconsider and or consult an architect who will advise you on the likely heat losses you will suffer.
Loss of heat through warm room air reaching the glass cooling then cool air falling back into the room for you to have to re heat air leakage heat lost through cracks in the frame or from ill fitting glass.