Gantt Chart

I'm tryin to create a gantt chart to use as a production plan, but i want to include line downtime. so if a line is off/down for two hours, it will extend the runtime by two hours. etc.. see email attached as to what i've got so far.

Basically if there is any downtime during the production time then extend the runtime, then check again if there is any further downtime during the extended runtime etc...