White Deposit On Slate Roof Underside

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Author Message   Old_school (Old_school) Senior Member Username: Old_school Post Number: 1234 Registered: 01-2009 Posted on Monday, August 12, 2019 - 07:40 pm:        Maybe its a silly question, but did they blow some cellulose insulation into the attic? What is the ventilation like? Old School   Rag (Rag) New member Username: Rag Post Number: 1 Registered: 07-2019 Posted on Wednesday, July 31, 2019 - 05:19 pm:        Hello: I am a CT home inspector purchasing a 1930's house with a slate roof in Burlington, VT. I hired a local inspector as "another set of eyes" and I worked alongside him this morning. I have no experience with slate roofs. We discovered a situation in the attic that we were unable to sort out. There was some white powdery deposits in the attic on the underside of the tongue-in-groove roof decking. It looks like efflorescence, it could be mold or it might be something completely different. There were not any active leaks observed and all was dry when tested with the moisture meter. Photos attached. Can anyone with slate roof experience provide some insight as to what might be going on here? Thanks in advance for your help! -- Rob --