The NEC does not regulate the insulation of houses. �AND the K&T wiring
is not new enough to be involved in a current inspection process. �I've
covered miles of it with insulation in multiple rentals. �Proper fusing
of the circuits is the key. �No overamperage= No heat. �You should just
go hang yourself with some single strand wire you pin headed *******.-

Currently the United States NEC forbids use of loose, blown-in, or
expanding foam insulation over K&T wiring.[5] This is because K&T is
designed to let heat dissipate to the surrounding air. As a result,
energy efficiency upgrades that involve insulating previously
uninsulated walls usually also require replacement of the wiring in
affected homes.

you must be buds realtive or something your rentals are at some risk
from fire.......

you need to check current codes, but heres the wikipedia reference

http://en.wikipedia.org/wiki/Knob_and_tube_wiring

As existing K&T wiring gets ever older, insurance companies may deny
coverage due to increased risk. Several companies will not write new
homeowners policies at all unless all K&T wiring is replaced or unless
an electrician has certified that the wiring is in good condition.