Wht substance on the rafters appears to be mold. There is poor ventilation and an HVAC system in the attic. I would recommend it be tested. What do you guys think?
It does not look like mold, more like lime such as concrete. Does it rub off?
Or even better, what does it taste like?
Couldn’t you say something to the effect “Unknown white substance, further testing is needed” or something like that. I personally do not know what it is but if you find out I would be interested in knowing.
If it was mold , it would not be just on one side of that rafter . It looks to be a recycled piece of lumber . Which quite common in framing a house . I would think it is concrete stuck on there . Would be much easier to tell in person . :D:D:D
Also looking again there appears to a problem with moister at joints on the brick wall . Seems like there is staining there , you might want to check the roof to wall connection . :D:D:D