We're in the process of renovating one of our ground floor rooms and when we
removed the ceiling we discovered one of the joists in the floor above has
been heavily damaged over the years by woodworm (which has been recently
treated). I can wiggle the joist around and it has the consistency of cork.
Two other joists are also damaged but still seem to have strength. My first
plan was to remove the damaged joist and install a new one but I've realised
this is going to be difficult since one end is imbedded into the exterior
wall and the other end imbedded into the sleeper (is that what it's called?)
running across the fireplace hearth. Would my best bet be to run new joists
in parallel with the existing ones using joist hangers? I've not used joist
hangers before, is there a write-up somewhere on the Internet on how to use
them? Thanks for any help. The link below is to some pictures of the
problem.

http://myweb.tiscali.co.uk/dbecker/joists.htm