I agree with Kim, The Law Society of BC website lays out the requirements clearly. http://www.lawsociety.bc.ca/docs/practice/resources/ClosedFiles.pdf
They also include a reporting letter to the client which is useful.
Finally, there is an “ownership of documents” resource which is helpful when weeding through paper files.
I believe Carina’s comment about scanning files upon closing (or even scanning document upon creation and intake, tagging the paper “scanned”) is the future for all law firms in order to avoid the time and expense of offsite paper storage.