Insulated render on old building

[photogav]

So I have a question about insulated exterior and interior render in a old Cornish granite based house.

I have been advised in order to up the EPC rating to get the place rendered with an insulating render - insulation board with a render over the top (I guess that's what it is) on the outside and inside.

My first question is this the right thing to do? I would have thought it would lock damp into the solid walls. Is there another way to achieve the same insulation with something that breathes naturally?

I hope someone can help?

 

[JP_]

What is the outside finish? External insulation might ruin a pretty house. Internal insulation boards might ruin a rustic internal finish. Either will work though, if rooms big, I'd do internal insulation.