Re: 90 year old house with knob and tube
A talented electrician who's willing to take time to think about what he's doing can fish new wires through old walls with minimal damage. You'll probably have some minor repairs to do, but it shouldn't require tearing out the walls & ceiling.
Hiring an electrician with a lot of experience in old houses (and whose references are happy with the workmanship) may be a lot cheaper than having to do major repairs to the walls & ceiling.
If you're doing it yourself, two tools that will help you: an electrician's fish tape, and fiberglass rods. These will help you to "fish" the wires through places without tearing it all up. Another tool that's helpful is a long, flexible drill bit (these are around 4-6 feet long). Greenlee's models are called something like "D'VersiBIT". The idea is that you can drill through the top or bottom plate on a wall using the existing outlet box hole for access.
You should have the wiring inspected; expect to pay for this service. A lot of the old knob-and-tube wiring has crumbling insulation, but if the insulation is good then it's not necessary to replace it.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.