36-year-old house in North Atlanta, GA, have lived here since 1997. Drywall on ceiling and walls in attached garage, garage floor on slab, unheated space. No laundry or utilities in the garage. No living space above, just a small attic. There are linear soffit vents and they are not blocked. There is a louvered 'window' vent on the side of the garage below the roof peak. We do not have insulation in this space.
No problems in garage for 12 years until 2009, had roof shingles replaced and ridge vent was installed. In late 2010, paint and seam tape started peeling and then a large chunk of ceiling drywall fell into the garage. Roofing company inspected and said there was no leak in the attic area. A contractor repaired hole and put additional nails along the other drywall sheets, re-taped, re-mudded, sanded and painted.
In 2015, paint and seam tape started peeling again in several spots of the garage ceiling, not just one area, and now there is a line of black mildew along one of the drywall joints toward the back of the garage, on the downward back slope from the peak. Roofing company out again, no leaks. They cannot/will not explain why we have this problem just since the ridge vent was installed. They just say it's not their problem.
I'm too old and DEFINITELY not a DIY-er to get up in that attic and look around myself. Before we tear out the ceiling and start over, any ideas what could be causing this and how to fix it? And what kind of company do I call to address it? Thank you!