Embers lodging on decks pose a very high risk of ignition.
Non-combustible decking materials
Non-combustible decking material will not burn. Use concrete stumps, metal framing and fire-retardant-treated timber.
Separation from the dwelling to prevent fire spread
If the deck is built with combustible material, non-combustible material should be placed between the deck and the house. This will reduce the possibility of the fire spreading between the deck and the house.
Construct with gaps between decking materials
Leaving gaps between the decking timbers will allow most embers to fall through. However, there is still a possibility of embers igniting at timber junction points. Ensure there is no fuel under the decking and that you have access to put out any spot fires underneath.