I’ve been deconstructing a house recently, and I came across something today I thought I’d share with the group. We had a discussion a couple of days ago how in leaky houses a lot of dust comes in with the exterior air (here: https://www.greenbuildingadvisor.com/question/closet-shelf-material-choice-and-indoor-air-quality )

Plus I just happened to read an article by Joe Lstiburek about dust:
https://www.buildingscience.com/documents/building-science-insights/bsi-114-smoke

He points out that warm air holds more dust than cold air, so you often get deposits in spots where air quickly changes temperature.

So attached are a couple of pictures I took today. The house was built circa 1926, originally had no insulation, much of the house is uninsulated and just leaky as can be. The insulation that is in was indifferently installed in general.  The first picture shows striping on two pieces of insulation, the sheathing was 1×8’s with significant gaps, you can see that as the warm air exited and cooled through the cracks dust precipitated out and left stripes. The second picture is a piece of insulation that was along an uninsulated section, you can see how discolored the edge of it is from the air passing by.

This house is noticeably dusty inside.