Twenty years ago I rented this house Ibought a new home recently and I'm in escrow now . When we rented the house we signed a one year lease for the past 18 years we have been on a month to month rental, I would like to know if I must give a 30 day notice of quit and what happens if I don't.

Yes, when you switch to month to month the terms of the lease remain in effect except for term and rental. Also, most states require notice of termination of the lease.

The amount of notice you need to give depends on the lease and local laws. Since you left out the key fact of where you are located we can't tell you want notice you have to give. Some states require a straight 30 days, others a full rental period.

If you don't give sufficient notice, you will owe the landlord for rental until the end of the legal rental period.

I guess after 18 years of renting, ( does anyone still have a copy of the original lease? )

But after 18 years, you should know the owner on first name basis, why not merely call and talk to them

To answer the first person ,the state in which I live is California. The answer to question is yes I have the original lease along with all letters he has sent to me. No I'm not on a first name basis with the man he like to remind me that he is the loanlord! Even thou I have tried to be he still calls me his tenant!! I shall call and tell the man I'm moving just wanted to know if Iwas required. Thank you

CA requires a straight 30 day notice.

To answer the first person ,the state in which I live is California. The answer to question is yes I have the orginal lease along with all letters he has sent to me. No I'm not on a first name basis with the man he like to remind me that he is the loanlord!! Even thou i have tryed to be he still calls me his tenant!!!! I shall call and tell the man I'm moving just wanted to know if Iwas required. Thank you

Don't just call him. Make sure you put it in writing.

I'd say with your warm loanlord vs tenant relationship I'd send that letter certified, return receipt requested