New electrical is better than real-old electrical with cloth insulation but not as good as 30-40 year old wiring with thicker copper wire and thicker plastic sheathing, so long as the sheathing isn't brittle. 

You find it in 1950s era flooring tile (usually the 9x9 ones), concrete/asbestos siding (durable but brittle), piping insulation, sometimes that 1920s insulbrick siding, as an additive to some old plasters, and probably half a dozen other places I have forgotten.

This compromise can be from heat caused by over loading,  heat caused by Added insulation (blown in cellulose) and brittle conductor and sheathing from past work.Utilization devices are a concern, most notably because K&T has no ground and either two prong devices are in place, or people have unsafely added three prong receptacles in their place. 

The old ones can get really brittle.

Fire damage can be tricky but from what I understand any framing that's at least 2/3 intact (not charred and brittle) can be salvaged.

The installer said that it is a brittle material because it is man made.

Galvanized is 50 years and copper gets pinholes and CPVC gets brittle.

Its beautiful but it was a beast to install because the planks were thinner and brittle.

Which may not work trying to marry the new shingles with old brittle shingles.

there is a state test kit that's just $7 or something like that. or at HD, you can get test kits.lead paint is a son of a biscuit. i never test it, hope for the best. i know that's not an excuse, but i paint over it. i think kills would encapsulate pretty much anything.my realtor once said "lead paint just peels in sheets. like wall paper kind of sheets, not brittle like normal latex paint". i have never seen what she described.i dont think i am helping you though... just rambling along.