sm_jamieson wrote:
I've never got the hang of when timber is going to be the size you ask
for and when it will be smaller, due to the method of sizing the
unfinished product. And it seems to vary around the UK. This never
mattered before.

Nope, *standard* timber sizes don't vary that much around the country.

Now, I have on my plans, sizes like 75mm x 225mm joists to fit into
matching joist hangers, and all the fittings should be tight. I will
order the timber from a proper merchants, since some is graded C24
etc, and must not warp.

If you can find any 'natural' timber guaranteed *NOT* to warp, let the group
know - BTW, that's why you use herring bone or solid strutting between the
joists to try and stop them moving too much.

So if I order 75mm wide joist hangers will the inside measurement be
exactly that ?

No necessarily - if the fit of the joist is too loose for your liking,
simply stick a packing piece on side or the other before fixing the said
joist!

BTW, why are you using 75mm (3") thick joists? The standard is usually 50mm
(2") - unless you are trimming around an opening such as a stair well.

Assuming it is, I need timber that is exactly 75mm wide. However, a
lot of timber is regularized and rounded on the corners, and is
probably smaller than the size you ask for.
What should I ask for to a) not look like an arse (no comments ...),
and b) get the finished sizes I need ?
In the Midlands.
Cheers,

If you joists and exact size - then simply ask for 'dimension sawn' timber -
and you will get what you want.

Cash