Soffit vents running the full length
Nothing at the top edge, although unlikely to be air tight
All I can feel over there is the void between brick and block
It's not a very big space. Seems a bit pointless really, just a great big chimney!
The joists are less than 3"x1.5"
The pitch is about 27 degrees.
That section is about 2.5m across the front of the garage.
I'm not ever expecting the garage to get really hot, it's more a case of not wanting it to get really cold. I might occasionally use the oil radiator if I'm in there working but mostly it's just the boiler and maybe the washing machine might be running.
Thanks for all the help.