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I've considered it but how do you solve the issue of the roof not overhanging the gable end wall enough already, let alone once you add further insulation.
We'd need to remove all render (cement), add insulation, render with lime, amend roof, sort gutters etc which is why internal is appealing as we're gutting everything anyway
apc-
This is our situation too, we would need to remove render, relocate drain pipes, insulate, re-render and deal shallow roof overhangs which would be non-existent after adding external insulation…
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Not sure how much of a pain extension the roof (rather, just the tiles) a but would be.
As to removing render - why bother? And you certainly wouldn't need to render over the insulation in lime. And good luck finding someone that can do lime render and insulation.
If it's inside you want, you would have to account for where the vapour boundary would land - you could end up with everything condensating between the insulation and outer wall.
Stud walls with air gaps would mitigate that, but you'd lose space.
andos
NotThamesWater
External insulation mitigates some of the risks of condensation and damp. And is less disruptive internally.