As I understand it, windows on an building do not have to be boarded up as long as the glass is in place. Once the glass is broken, the owner can either replace the glass or put up boards. The requirement is that the building not be open for trespass.

[City Code reference: Sec. 37-2-2. [[b) ...a dwelling shall be considered abandoned if: [[1) That dwelling is vacant, dilapidated and open at the door or window, leaving the interior of the building exposed to the elements or accessible to entrance by trespassers...
Sec. 37-2-3. [[a) It shall be unlawful for any owner or agent thereof to keep or maintain any dwelling which shall be [[1) vacant and open to trespass...]