As you surely already know, by regulation you’re required to maintain your accounting records for a certain period of time (i.e. 7 or 10 years, the length depends on your local requirements). 

In order to meet those requirements it’s customary to have the documents stored, archived in a safe location. By definition the word “safe” in here means a location where the documents can be maintained in a form they could be readable after the determined time period. They should be kept safe from possible fires, floods etc. Those documents should also be stored in a location they cannot be stolen or otherwise accessed by persons not authorized. Also make sure the print and any writing is also visible after the time period has elapsed.

In case your documentation is digital and not on paper, you need not worry about fire per say, but keep in mind that any physical copy is still exposed to physical destructions. What you also ought to worry about when it comes to storing your data electronically, is the accessibility of the drivers (hard-drives, USB drivers, CD, DVD etc.) or whatever source you’re using to store the documents. After a while they may become unreadable so ensuring they still have all the data should be a regular process (and obviously making back-ups of everything).