To get Ash Plank in RuneScape: Dragonwilds, craft it at the Sawmill from 1 Ash Logs.
What is Ash Plank used for?
Ash Plank is used to make 86 items, including 30° Inverted Roof Support Wall, 30° Roof Support Wall, 45° Inverted Roof Support Wall and 45° Roof Support Wall.