Do I need to rewire?

We moved into a 30 year old house a couple of years ago. We got the fuse board changed over to a switch system last year. The electrician told us that while the board is earthed, the switches and light fittings are not. One consequence of this, he told us, is that we shouldn't use metal light fittings. Also, the wiring for the hanging lights is not the familiar 3 core flex but 2 thin wires wound around each other.
We are starting a large extension later this month which will take 3 - 4 months. We intend to move out for the majority of the build as we have 2 young kids.There will be an electrician on site for some of that time and we intend to get him to earth anything which isn't already earthed. How big of a job is this? While we are at it, should we get the whole house rewired? If we do not, will it need rewiring at some point in the future?

I'd advise you to go ahead and do it while you have this opportunity. Take the time beforehand to look at all the outlet and switch positions and decide if you'd like to move any, put in extra lighting, sockets etc. Add in audio/ network cabling while you're at it.
Leo

Another factor to consider is the cost. Rewiring the house will cost at least €5k.

Two comments:

If the wiring is 30 years old it is overdue for replacement.

What would be the cost of a fire caused by faulty wiring?

Maybe hard facts to stomach, but Leo is quite right that now is the time to do it.

also see thread or RECI or not RECI - maybe of use.

ps. rewire!

If you are looking for a good electrician, try Mark Fox Ph 01-822 4654/ 087 965 4521. He is RECI certified.

I'd concur with all the above and suggest a complete rewire- the existing lampholders are very old indeed. My brother is an electrician and I know that he would not even consider wiring an extension where the wiring in the main house was to be left alone, given its age. As suggested by Leo it is an excellent opportunity to incorporate additional sockets and services. It will also allow you to incorporate a proper mains wired smoke detector at each floor level and if you want a burglar alarm you can include this also.