This section shall not apply to horizontal sliding doors. Existing dead bolts of at least one-half inch in length shall satisfy the requirements of this section. Existing locks with a thumb-turn deadlock that have a strike plate attached to the doorjamb and a latch bolt that is held in a vertical position by a guard bolt, a plunger, or an auxiliary mechanism shall also satisfy the requirements of this section. These locks, however, shall be replaced with a dead bolt at least 13 / 16 of an inch in length the first time after July 1, 1998, that the lock requires repair or replacement.