Sub frame for deck

Cmar-Ireland

I'm about to start building a deck in the back garden of our house. It will be roughly T shaped, approx 8m by 8m.

The height of the deck will be determined by the step at the french doors from the dining room. This step is only 130mm higher that the concrete path outside. So I cannot use 50x100mm framing. The deck boards are 35mm thick.

Would it be ok to use 50x75mm framing once it has plenty of footings? Once the deck goes over the grass area I have the height to use 50x100mm joists.

Thanks

cork2

75x50 isnt really a joisting timber. how were you thinking of fixing it down?

Cmar-Ireland

The 75x50 joist will be bolted to the wall as a ledger with expanding bolts. Then 400 on centers for the joists.
The area to cover is 3m x 3m then I have the height to use 100x50 joists for the rest of the deck.

Where I have to use the 75mm joists is all over concrete, so I can use that as a solid base for posts.

cork2

the 75x50 should hold tonce you use plenty of legs under it. where you have the height you would be better off using something bigger than 100x50 the bigger the timber the less chance of a bounce! and make sure all timber is pressure treated and anything touching the ground has dpc under it

Cmar-Ireland

Yeah, there will be plenty of legs under the smaller joists. It's 3m x 3m in a U shape. So three sides will have the 75mm ledgers and joists in between.
Should I just put a cut off of dpc under each leg?
I'm using PT timber and will be treating cut ends with a sealer.
Due to the shape of it I'll be using joist hangers for the cross members.

On a 3m span, with wall anchored ledgers each side, would one leg in the middle of each cross member be enough or should I put two per joist?