As highlighted by Stephen Quirk this is an inferior form of construction as the cladding is not separated from the structure by a drained cavity. This being the case water exclusion is reliant firstly on the render and more importantly on the breather membrane (Infiltration barrier), especially where cracks have developed as these will tend to draw in water by capillary cation.

If the render is of breatherable lime, this should allow moisture to evaporate unless it has been sealed with a plastic paint?

It therefore appears to be the case that the serviceable life of the cladding is determined by the infiltration layer, and unless the material is known the remaining serviceable life cannot be predicted.

Interestingly modern comparable materials such as Tyvek Structure Guard are said to have “a lifetime equal to the building element in which it is installed” However 20 years ago things may have been different in the USA.

The fact that the render has cracked in multiple places suggests that thus is overly rigid and/or un-reinforced (metal or plastic) as is now considered to be good practice when render is applied to a flexible background (ie the sheathing layer of a timber-framing building).

Given the above I would suggest reporting that the remaining serviceable life of the cladding is limited and that periodic maintenance will be needed until it is eventually replaced. In the meantime, the existing cracks should be repaired using a pliable material to match the original materials, which may include plastic mesh to prevent re-occurrence.

Personally, I believe the best form of cladding for timber-framed buildings is timber (eg weatherboard) but thats another issue, but could be considered if and when the walls are eventually re-clad. This is the usual cladding for timber-framed  “Colt” houses in the SE.

The roof tiles definitely have a limited remaining serviceable as bitumen generally is not a long-lasting material.  Even high-performance bitumen lasts no longer than about 40 years. I would check these close hand to assess the condition and whether or not they are becoming brittle.

Hope this is of  interest