My plumbing is on the attic and my roof is very low,the pipes ,for hot and cold water are galvanized and very old,I would like to replace them with PVC schedule 40 for cold water and Chlorinated PVC schedule 40 for hot water,is this a good idea ? Please reply,thanks .

Good morning,  PVC for cold  and CPVC for hot works for me.  To connect back to galvanized, use famale PVC adapters if connecting to male threads or male adaptors if connecting to a galvanized fitting.  Be aware that when you disturb the galvanized pipeing that you may dislodge the mineral build up in the old pipes.  This may clog up the screens on your aerators or the ports in the faucet cartridges. This may mean flushing out the supply lines if any faucet starts to run slow. Good luck, Tom

PVC and CPVC are cheap and easy to work with for the inexperienced, requiring little in special tools. They will even bend a little to make up for not quite cutting the length right. You do not want to install them with too much strain, but a little is OK.

Old galvanized pipe can be hard to get apart. Just putting a longer pipe on your pipe wrench can twist off a pipe you were going to leave because you couldn't get at the other end. Heating a joint with a torch and then quenching helps. So does hammering on the joint.