Home in Cincinnati built in 1919 according to a friend. He has come across an underlayment between unfinished basement joist and subfloor. Card board like/fibrous and thick. Was it a vapor barrier, sound deadening material or what?
Curious what the forum has to say.
My first thought is an asbestos based material, possibly as an air/insect barrier. Also some mighty fine K&T wiring to pair it with.
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Possibly “plenum material” for a return air duct between the joists?
Is that open duct in the picture a return air? If it is my WAG would be that the cardboard material was used as ductwork.
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Yeah, probably loaded with asbestos. I’d guess it’s insulation for heat or sound but don’t ever recall seeing it before.
My Mag is it is a vapor barrier to help protect the hardwood floors above. It looks like it was placed on top of the floor joist before laying down the flooring. I’m not sure. Just throwing it out there. 
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1/4 inch masonite looked a lot like that when it got old, but I never saw it used in that app;ication
Sure looks like it was a duct, based on the dust build-up on the wires.
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so the house is over a hundred years old and you are suprised at the dust build up ? would You like me to send You a picture of my five year old floor joists???
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Don’t you lick yours to keep them dust-free??
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That build-up looks suspiciously like what happens in a duct, in my opinion. And it looks like a hole is cut int the top of the apparent duct below. But, who knows.
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In my area I have a lab, can take a sample to, and get results back in 24 hours, for asbestos. They put it under a microscope.
contrary to popular opinion I dont just go around licking everything…it is a scientific method for testing in many applications but certainly not everything…
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I saw nothing in those pictures that made me think ACM, but perhaps You saw something that is not apparent in the pictures…
Surprised you didn’t request the “lick test.” It works on everything doesn’t it? 
thats a negative ghost rider…
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I agree. Sometimes I see remnants of this stuff or partially intact. None that I have seen recently is still viable and has been replaced with more modern metal duct just like you pointed out. None that I have seen resembles asbestos but I have never had it tested. Too bad this was a drive by posting, I would like to see more pictures. (such as was this material in all the floor joist bays or just a few?)
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This is not a drive by. Was waiting for more information. The material in question is in fact throughout not only in basement but so far between first and second floor as well and can only assume at the moment that it is between second and third floor.
Friend is not looking to have material tested for asbestos but really wanted to know what it was and why it was installed between top of joist and sub flooring. I have not seen this yet in any inspections so I was wondering if there was someone in the forum that did. He is wanting to soundproof and insulate between floors as this will be a two family home. fyi: all knob and tube remnants are being removed and new wiring installed throughout.
I thank all that responded for their insight and comments.
Tom Foley
New York Home Inspector
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Another possibility, being that it was installed on multiple floors over the joists, is an early form of Rosin or Felt Paper.
On another note, and not questioning the knowledge of our friend or his statement, but many homes built during that time period didn’t have “sub-flooring” but instead the hardwood floors were attached directly to the floor joists.
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