Fire line in new vaulted roof extension

[DIYer Damo]

Hi,
I've a new ground floor extension and i'm ready to board underside of roof. It's a vaulted warm roof with velux windows. I've 100mm insulation between rafters and was told to add 27mm thermo board to underside of roof. Does this 27mm themo board also need to be fire lined? Rest of downstairs in house (restoration) we've dropped ceilings and used 15mm fireline + double board over rsj's. Seems weird that the extension roof would just have 27mm thermo board?

Cheers

 

[23vc]

If the rest of it’s a habitable area above the ceiling then that’s why it needs fireline boards.