In message , at 11:54:22 on Fri, 21 Jun
2019, Andrew remarked:

If you mean a half brick, I should recommend a maximum height of
about 900mm without buttresses.

From a structural point of view, single-brick garages don't seen to
fall down very often. But some modest buttresses would be OK as long
as they don't prejudice the insulation value. Any vertical loading
applied inside would be carried by the studwork, so we are mainly
interested in the brick wall not topping over.

If it is just a single run of wall then you will need to buttress
it. If there is a right-angle joint then triangualtion will
provide the necessary strength.

It would have right-angles at both ends.

If this is going to be habitable, then building control will
want to see plans with calculations for structure and thermal
performance anyway.

I know, but trying to get some rough idea before spending a lot of time
on proposals that won't fly (or indeed caving into unimaginative
suppliers who want an easy life).
--
Roland Perry