Roger Mills wrote:
In an earlier contribution to this discussion,
Phil L wrote:

If you are changing the use of the garage to a dwelling area, then
planning and/or building control will need to know, they'll also want
to see the foundations which will mean diging some test holes
outside, they'll want to know if there's any DPM underneath the
existing floor and if there's not you may have to dig it out and get
one in and probably insulation under the floor too, and also the
walls and ceiling.

The foundations shouldn't be too much of a problem. There probably aren't
any across the doorway - but there won't be much to support anyway - just
the brickwork in the lower part of the doorway and the window. The concrete
floor will support that ok. Everything higher up is supported by the lintel
which, in turn is supported by the brickwork and foundations either side of
the door.

When I did a similar project, the building control officer made me
excavate the ground immediately outside what would be your door area to
confirm how thick the concrete floor was, before giving me the OK not to
prepare new foundations.

The garage floor is almost certainly several inches lower than that of the
adjoining rooms, and will need to be made up to house level - so there is
plenty of scope for installing a DPM and insulation if required.

Suggest the BCO is consulted over this too before work gets under way...
for current regs, several inches of insulation plus the overlying
concrete (presumably) will be required; I think the OP would be lucky to
have that much depth available. However, my BCO was prepared to
compromise over this as it wasn't a new build, and I got away with 1"
Kingspan (ie 1" more than elsewhere in the property! which is likely to
be the same scenario with yours if it's 1960s).

Once you've submitted a building notice to the council, and paid your
fee, you'll probably find the BCO will be prepared to come round and
advise on what he expects. They're usually pretty helpful IMHE, if you
show you're trying to do it properly (and actually bothering to submit a
building notice in the first place is the first step in that process!)

David