The earliest commonly used wiring method that is still in use is knob and tube. We could find ourselves in a home built as late as the early 1970s with knob and tube wiring. Knob and tube wiring may be installed today as an extension of existing knob and tube wiring or by permission from the local building department. One characteristic of homes built when knob and tubve was popular was a lack of (or minimal) thermal insulation. Covering knob and tube with thermal insulation is a bad idea but not necessarily for the reason many of us believe.