Balau, certainly a timber to get you called back, this has caused most I know in the trade to have movement issues, There are many cost effectice solutions that would be a much better bet, better stability too.
Always best never to any substructure touching the ground and the bigger the void under the deck the longer it will last. This is because a larger space under the deck will allow greater air circulation and thus the understructure will dryout quicker after rain.
Screws would be best in stainless, carpenters mate number 10 Bugle head, 63mm x 4.8mm.
If you mail me a plan of the deck I can advise upon EC5 spans for the substructure.
basics here https://deckingnetwork.com/decking-substructure/
spec’Â here https://deckingnetwork.com/decking-resources/
Karl
