In message , tzd3sw
writes
I'm building a thermalite wall between my garage and what will be a
utility room. This wall will have a door through. What size gap should
I leave for the door and frame ? Is there a standard size ? This will
be a firedoor if it makes any difference.


Many thanks.

I'm not sure about standard sizes but the ones I recently bought are 30"
X 78"
Two points I found when I had a similar situation were.
Firstly the BCO insisted on an automatic door closer, I used one
of the spring loaded chains that fitted into the hinge side of the door.

Secondly it was also necessary to have a step down into the
garage from the utility room so that any fuel spills in the garage could
not flow into the house.
--
Bill