Better to Insulate flat roof or solid wall?

[brianthebuilder]

30 year old extension in conservation area.

Which is losing most heat and which will pay off best in effort and warmth?

- Flat roof (in good nick outside) is 6' 8" long and 10' wide. Joins onto house as part of bigger room

- Solid wall is 11' wide by 8' high. Only outside wall as end of extension is wooden french windows covered by interlined curtains. Insulating would lose 3-5 inches of room depth. I do have interlined curtains that would cover the wall - but not our first choice and anyway how effective would this be? Wall is not exposed as paralled by garage wall 4 ' away.

 

[Monkeh]

Heat rises.

 

[Deluks]

Heat does rise, but it also dissipates when it comes into contact with something cold. This is why we also insulate floors, but to answer the OP, do both. 3 sheets of insulated PB will see to that wall, doing the ceiling/roof will likely involve disruption anyway so why skimp when you can sort it in one hit?