A recent 2 story 40 year 8 plex inspection with 4 units on a slab had serious ventilation problems. With condensation (moisture) on most of the vinyl dual pane windows I knew there  would likely be some issues. The rear wall had mold & rot, inside & out,  at the floor, with some deterioration 12" up the wall. Moisture readings of 15% to 20% throughout 2 of the 4 units indicate a serious moisture problem. Kitchen fans vented inside while baths had functional fans moving little air. The were no visible ducts on the exterior walls for the 4 ground floor units. Where was bath moisture going? It was not going to the exterior. The upper baths were venting into the attic. I assume relative humidity on the ground floor was well above 60%. Moisturereading below was 50% on the exterior (T1-11 siding) and 25% to 30% inside gypsum.