Calculating an asbestos roof in analyzing a deal

[Curran D Bishop]

I'm considering a deal that has an asbestos roof that was put in in 1900. It's still in good condition, but I'm seeing estimates that asbestos roofs are good for "50 years or more"; I had a friend with one that he called a "100 year roof"; that's great, but this roof is 120 years old...

At some point it's going to have to be replaced, is there any way of estimating costs on that?

Also, from the info I've found in a quick google search, asbestos was used from the 1930s-1970s; so I'm curious why a house built in 1900 has an asbestos roof--was there a long-lived material that preceded asbestos that inspectors confuse with asbestos? I.e. is this mislabeled (because they didn't use asbestos in 1900 and it's something else), or does the current owner have the install date wrong (the asbestos roof was put on sometime after 1930, not 1900, because they didn't use asbestos back then) or do I just have bad info that asbestos wasn't around in 1900?

And what does that looks like: do people just roof over them, or is some other step required? And is that having the EPA come in hazmat suits and remove the asbestos roof? I saw a comment somewhere that asbestos roofing was less hazardous than siding and was generally just removed like old roofing...