I want to rewire a detached garage with knob and tube wiring. The Garage is only three feet from the house. The two wires running overhead. How do I run conduit between the house and garage? I'm not able to run underground do to concrete sidewalk.

Maybe there are additional methods... but In my opinion the best method would be to remove part of this sidewalk and install the conduit underneath. Not the easiest I realize but I believe the safest and most appropriate...

Check with your building dept and they can tell you if it is legal in your area.

I am not an electrician but think as long as span is only about 3 feet and high enough not to be interfered with by anything from the ground, you should be fine.

Chuck

You may be able to tunnel under the sidewalk or even better- be able to drive an appropriately sized steel conduit under, or a slightly larger sleeve, then a conduit as required for the conductors inside the steel sleeve if you are concerned about damage to the steel sleeve/conduit while driving it forward.
This is done on a large scale by utility companies everyday under roadways when open cut is not permitted. Usually referred to as bore and jack. They sometimes install facilities of maybe 50 to 100 feet in length between pits. Three feet doesn't seem too bad.
All depends on what you want, and I am assuming you can access both sides of the walkway.