On 18 July, 09:39, Simon wrote:
///

Thanks, other thing, I was wondering whether to use 50mm thick ledger
plate or 75mm.
Anyone know what is usually used ?

How long is this wall plate and what load is it supporting? How many
joists are butting onto the wall plate?

Problem that has to be solved is similar to designing joists to
support a floor.

I may be misunderstanding something about the requirement here, but in
general I am sceptical that just willy-nilly putting up a wall plate
and fixing n joists to it via thin metal
joist 'hangers' will stand the test of time.

For starters, thin style hangers are used to hold joists into notches
in the wall plate. Otherwise joist hangers made from thick (c.3mm)
steel plate should be used.

The method of fixing the wall plate, distance between bolts, and size
of bolts needs determining based on the load to be carried.

Whether 50mm or 75mm, or some other size is needed depends on these
considerations. As does the depth of the wall plate.

HTH