Firms have traditionally struggled with the creation and implementation of a records retention policy.  As an alternative option to consider - pass the storage costs on to your clients.  I know you are probably struggling with getting clients to pay for traditional cost recovery items, but if you are charging for copies, prints, scans, etc. then technically, the documents belong to the client.  Think about addressing the following in the client engagement letter:  Outline how you will dispose of their records.  Consider the following options:

• All documents will be shipped to the expense at the conclusion of the case at their expense
• Firm will retain these documents for the client based on your records retention policy until DATE at a rate of $x/month/box after which they will be destroyed at a rate of $x/box
• Firm will retain these documents for the client based on the Firm’s records retention policy until DATE at a rate of $x/month/box after which they will be destroyed at a rate of $x/box
• Firm will destroy all documents at a rate of $x/box
• The client can select which option they want to utilize at the beginning of the engagement. If at the end, then an “unless instructed otherwise” option should be included

Source: http://matternoffact.com/post/815463817