IRB approval of a protocol typically lasts about one year. Each year the protocol must be renewed. Approximately 2-3 months before your protocol's expiration date the IRB will send you a memo requesting renewal documents. Approximately 1-2 months before the expiration date you will receive a final reminder memo. Once the IRB has received these documents they will be reviewed. The IRB will send the approved renewal documents near the expiration date.
If you don't respond to the memo and your protocol expires, the IRB is required to close your approved protocol and your research activities must cease. Once a protocol has expired, you must submit a new IRB Application and start the approval process again.