Hi @carpenterman,
Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Being in Australia, I am not as familiar with New Zealand's building standards, but the NZ Timber Preservation Council Hazard Class Description states that H3.2 treatment can be "used outdoors above ground, exposed to weather or protected from the weather but with a risk of water entrapment; i.e. decking, fencing and pergolas."
This 140 x 45mm SG8 H3.2 KD Treated Radiata Timber Framing would be a good option for joists.
Let me know if you have any further questions.
Jacob
