"Icky" wrote in message ...
I'm considering breaking through the cavity breezeblock wall between my hall
and my garage and fitting an external door between them (an external door
is required, I'm told.)

You need a fire door not an external door. Make sure it is 1 hour
rated at least (but I'm not sure on that) and use intumescent strips
in the frame and a door closer. It is a garage you are letting into
your house. Somewhere that you store chemicals and put machinery
loaded with petrol. So use draught excluders too.

Also, any tips would be appreciated about keeping the rest of my house
in place while cutting this doorway.

Anything the wall is supporting will need proppng up. You can use
accro's or just 3X2's or whatever, under a cross piece (both sides).
You can use wood as a lintle too. It aught to be treated with
preservative or be a timber that is impervious to whatever. It is not
a good idea to use wood in a sealed wall though. Concrete is not that
heavy. Are you sure you are up to the job?

You might want to seal a section of the house off with polythene to
prevent dust. Keep doors and windows closed to stop through draughts
etc. If you start in the garage you can carry your debris out that
way.