Hi all
Just an update really...
Well, I spoke with the structural engineer yesterday - and his first reaction when I mentioned foam was ' no....!' - but I showed him the certificate of agrement info, and said that Renotherm said they would fix any problems with the roof first. He then went quiet - and said he could not honestly think of any good reason why not to use it.
I checked with Ronotherm and they told me the foam is breathable - so even though the timber in my roof is not rotten, if any damp did ever get into the timber then it could still breath.
I have also challenged the company with the issue of tiles craking in hard frosts... and am waiting for an answer....
Regards, Simon.