He's painting his house and has discovered some rot in wooden soffits, that a previous owner has obviously just painted over to hide the rot.
My guess is it got this way from a leaking roof, but that has been recently replaced, so the cause of the rot should (hopefully) be gone.
The rotten piece in the photo is one long, 3 or 4-metre length that is crumbling away. The rot is far, far beyond "scrape out the rotten bits, drench it in Metalex, and bog it" levels.
Would anyone have any bright ideas as to how this could be replaced without either lifting the roofing iron or removing the guttering? Both of these options are not realistic at the moment.