___________________________  
|                          | ← Chimney (flashing lapped 2" up)  
|                          |  
|  Z-bar + 1" air gap → |  | ← Siding (fiber cement/PVC or primed wood)  
|__________________________|  
   ↓  
24-gauge flashing (4" onto roof)  
   ↓  
Ice/water shield (3' up roof)