First question - my first stopping place for insulation u values was
the DIY Wiki. They don't seem to be there which surprised me - or
should I have looked elsewhere other than in the obvious place
'Insulation' ?

The reason for the calculations is convincing a disbeliever that he
should insulate his workshop. Single brick structure, to be lined
with OSB on a 75mm framing. But how do I calculate the heatloss
across such a 75mm cavity without any insulation - do I need to take
into account convection ?

Any helpers please

Thanks
Rob