MikeG.
Established Member
AJB Temple":z9gz7uce said:........The oak I have is already planked and has been seasoning indoors for about 30 years.........
That changes everything. Crack on.
You won't be adding insulation, as there will be airflow behind it. You are simply adding shelter. It is critical to maintain the existing airflow behind the current cladding, to have a decent insect proofing strategy for your new void, and to produce a reasonable looking detail for the junction of the the cladding with the plinth. It really does look awkward to have the cladding sticking out 2 or 3 inches from the masonry. You know without me telling you that leaving existing rot in place hidden behind a new layer isn't a good idea, so deal with that first.
That aside, you've no good reason not to do this.