My head is spinning from all the different opinions I've received from local builders and other sources.
We have an old stone farmhouse, and all the eco-people are saying the walls need to breathe both on the inside and outside.
Some builders have commented that as long as you don't have obvious water damage visible on the walls (we don't), you don't really need to worry about breathability. One recommended putting battens and conventional insulation boards on the inside of the walls, covering the old gypsum plaster, and not even worry about replacing it.
Another very experienced plasterer wanted to take the wall back only to the layer of sand cement, and then put wood insulation and then lime plaster on top of that, supposedly making the wall breathable. That doesn't make sense to me give sand cement isn't breathable.
I haven't had one source say at the outset, go back to the stone wall and only then build it up with lime plaster and some type of insulation. Everyone seems to be more concerned with cost or effort than the issue of breathability.
Are these builders right in not worrying about the overall breathability of the wall? Perhaps there is some wisdom in them not seeing any water ingress and going from there.
If the eco-people are right, why is it ok to use non-breathable insulation on a modern timber/brick wall? Why should one jump to breathable and more expensive materials only for an old stone wall if you can assume the water ingress is as likely as it would be for a modern wall?
Both sides have so many assumptions, it would be nice to see a full list of pros and cons spelled out in a logical manner!
