Hi, I am renovating a 1920s rowhome in Philadelphia, and one room on the top floor (2nd) has this reddish dust accumulating in one corner of the room. This side has been damp for a while with a leak, but a new roof was put on exactly 12 months ago and it’s been drying up and no leaks from rain anymore. But this reddish dust keeps accumulating here. It’s quite soft material, I poked a hole in the saggy moisture damaged ceiling to see under, but it seems like it’s just cellulose insulation. What could be falling that’s reddish… doesn’t feel like brick dust.