12v lighting on a domestic environment

I'm not so sure of the advantages of 12V - at one twentieth of the voltage you need twenty times the current to provide the same power - e.g. 12W at 12V is 1A - compared with just 50mA at 240V. So if anything the risk of fire probably increases rather than decreases. In the original part P of the building regs, ELV lighting (with a few exceptions) was notifiable because of these risks. The increased current also means increased voltage drop - so likely to need larger conductors rather than smaller ones. Also you'll likely close the door to some of the safety devices that can reduce those risks - RCDs or even AFDDs. If you're thinking of 12V d.c. then be aware that d.c. arcs are much harder to break than a.c. ones - so in some cases you may need specifically d.c. rated accessories (esp. switches and protective devices).

If it were me I'd probably just protect the wiring system - e.g. with earthed steel conduit (even flexible steel conduit would do - and not that difficult to install really), with suitable steel boxes behind ceiling accessories. In the old days MICC/pyro wiring might have been another option, but that's pretty rare these days.  Just keep it all on the warm side of any thermal insulation to avoid problems with condensation.

   - Andy.

I'm not so sure of the advantages of 12V - at one twentieth of the voltage you need twenty times the current to provide the same power - e.g. 12W at 12V is 1A - compared with just 50mA at 240V. So if anything the risk of fire probably increases rather than decreases. In the original part P of the building regs, ELV lighting (with a few exceptions) was notifiable because of these risks. The increased current also means increased voltage drop - so likely to need larger conductors rather than smaller ones. Also you'll likely close the door to some of the safety devices that can reduce those risks - RCDs or even AFDDs. If you're thinking of 12V d.c. then be aware that d.c. arcs are much harder to break than a.c. ones - so in some cases you may need specifically d.c. rated accessories (esp. switches and protective devices).

If it were me I'd probably just protect the wiring system - e.g. with earthed steel conduit (even flexible steel conduit would do - and not that difficult to install really), with suitable steel boxes behind ceiling accessories. In the old days MICC/pyro wiring might have been another option, but that's pretty rare these days.  Just keep it all on the warm side of any thermal insulation to avoid problems with condensation.

   - Andy.