In Wales we have had a tendency to design our houses with the minimal amount of overhang on the roof. The tiles sit very close to the walls. This has meant that anything else that we add to the depth of the walls loses precious protection for the wall plate. So rendering and over cladding often has the unintended consequence of making the inner wall more liable to water ingress. Where the over cladding is water proof this can easily trap wind driven rain / overflow from blocked guttering into the structure.
I was in a house last week where the fascias have been twisted and are now potentially channelling water into the building. Another building around the corner from the centre is also suffering after the owners installed external wall insulation. Here the builders had put one of those awful plastic covers over the top of the insulation to ‘provide protection’ against rain. Surprise, surprise a few months later they were back extending the roof to do the job properly! Wind and rain are a potent force in Wales!
The junction between roof and wall is one of the weakest in a house and so we must be very strict about how we protect walls from the elements. Extending the roof line may seem like a costly addition to any work on the external walls, but if you are doing work on them it may actually save you money if you get it done at the same time. Certainly it would have saved the people around the corner a pretty packet on their scaffolding costs!
If you look at houses on the continent, most have large roof overhangs. This helps to protect the building fabric, provides shading against the summer sun (and with climate change we might even get some of this at some point!), gives additional shelter for windows etc. Learning a lesson or two from the near continent is always a good idea.