Hugo Nebula coughed up some electrons that declared:

Mike wrote:
I'm planning on building a new large shed, hopefully with low heating
requirements and a steady temperature all year round to enable me to
use it for woodworking projects.

The shed will be around 0.5m from a shared boundary fence and at least
5m from any existing structures. Will a mainly timber frame structure
covered in fibre cement weatherboarding (with a green roof of sedums)
meet class 0 standards or will I need plasterboard on all the inner
surfaces?

When you say 'large', anything with a floor area more than 15m^2 that
close to the boundary will require a Building Regulations application.
Also check about Planning. If it were more than 1m from a boundary, it
could be up to 30m^2 and still be exempt from Building Regulations.

From my research, 5m (as mentioned by the OP) from the existing house
avoids the building being deducted from permitted development, weird stuff
like conservation areas notwithstanding.

Thanks for the heads up on the 1m rule. I've had a b***er of a job trying to
find a site for my proposed shed/workshop that get's by on a "no
permission" basis.

Although I've not seen many sheds that aren't against a boundary (or
certainly withing 0.5m) - have you ever known anyone be busted for such an
offence?

snip

A timber framed building should have a vapour barrier on the warm side
of the insulation. The plywood or other sheathing should be on the
outside of the studs, with breather membrane to the outside of that, and
a ventilated and drained cavity inside of the cladding.

That's useful to know.

Cheers

Tim