Re: vinyl siding of existing wood
Vinyl siding has small weep holes on the underside where two sections join. These holes are designed to let moisture out, but if pressure washing they can let water in if the stream is aimed upward. That's why its best to wash with the water only pointed down, standing on ladders when needed to keep the water angle correct. The weep holes will also get clogged over time with debris (sawdust, spiderwebs, deceased bugs) So they can be keeping water in. Not good. Your structure could be quite damp. A workman can pull a few courses of siding and assess the situation; the openings will then allow for faster drying.
There could of course be mold. Worse still, rot could have taken hold.
Remove not the ancient landmark, which your fathers have set.