Worse case of mildew/mold I’ve ever seen
Disclaimer: I didn’t test for mold so I have to call it mildew.
Picture below was taken in the attic space of a 300-year-old house with a newly installed roof. There’s so much moisture in the plywood its delaminated. If the plywood can’t be cleaned and salvaged a new roof with new sheathing will be required.
Below is one of the attic windows, note all the moisture…dripping. Exterior temperature this morning was 27 degrees. The moisture problem has to due with very little insulation and a very porous home. The orignal windows are single pane double hung.