I am planning a deck that will be 4400mm X 2050 mm with 150mm ground clearance outside my laundry. I think we will use stirrups sunk into concrete. We can bolt a long timber into both the wall and the house. We are planning to use lightweight composite decking. Would you be able to suggest the best timber to use and the spacing of the stirrups. I am also planning a shower in the corner so would have a sump below that - maybe filled with gravel. I have attached a picture of the area
Welcome to the Bunnings Workshop community. It's wonderful to have you join us, and thank you for sharing your question about your deck.
If we do a quick calculation of the space available you'll be able to determine the timber size you can use. If for example, you use 90 x 45 plus the decking panel which is 23mm you will have a total of 113mm. If we take away this amount from your available space of 150mm you'll have a gap of 37mm. Since you only have this much space left, using bigger timber will not be possible.
I suggest having a look at this guide - How to build a deck by @MitchellMc. You'll be able to pick up some excellent pointers on spacing and footing for your deck frame. In reference to the shower, will it be an exposed or covered outdoor shower? It's important that the drainage for this shower be properly installed so that water will not flow under the deck. Trapped moisture under the deck will damage the timber framing and greatly reduce the life of your deck.
I also suggest having a look at the Bunnings deck-building guide: