The general rule in most places is that any circuits that aren't modified as part of the new work don't need to be brought up to modern code. The main service p

The general rule in most places is that any circuits that aren't modified as part of the new work don't need to be brought up to modern code. The main service panel is the main thing that ends up needing to be upgraded incidentally, since all circuits depend on it, and that can easily be more expensive than the actual work being done. But that only needs to be done once, and many old houses will want it upgraded anyway to allow for more circuits to be added than the box was originally designed to accommodate. However, I think the 10 years is a bit pessimistic. At least in the US, the code hasn't changed that much in the last 20-30 years, and many of the changes are at the periphery where they are easy to modify like GFCIs, and tamper resistant outlets, etc, so I wouldn't be afraid of making modifications to existing circuits for houses in that range. Older than that you start running into (AA-1350) aluminum wiring (35 years or older) or two-conductor wiring (65 years or older), and you'll want to take the policy of not touching those old circuits unless you plan on completely replacing them.