i might have this wrong but i always thought that part l was legal requirements in new buildings and only best guidance on any changes to existing systems due to financial and practical restraints. im not 100% though. I mean they change reg's so many times without thinking about the practical and financial implications, that when they revert back to the old system it makes you wonder how considered these changes are. I can understand with health and safety issues to a point, but even this has been changed back and forward so many times over the last few years. A good example of this would be the change of the regs regarding electrical consumer units, such as every mcb circuit must be protected by rcd with 30ma trip. 16th edition regs 2004. sounded great, until the finally realized that when a light bulb blows, it would trip the consumer unit and given most light are only used when its dark, you can see the potential problems. lots of old people hurt trying to get down the stairs in the pitch black to try to reset their consumer unit. There were even deaths (no joke). ironic that probably more people died through these new safety regs than would have occurred if the changes were not implemented. regs were quickly watered down and in a lot of cases changed back. now with the latest 17th edition being twice the size of previous editions such as 12 and 13 there is no clear definition of what is right or wrong. terminology like "functional provision", "Best practice" and "future proof" is just wording banded together with supplements and amendments attached to try and make sense of what it was they were trying to achieve. Electricians trying there best with what they know whilst reading the latest amendments on which consumer unit to fit in which house, most times falling back onto best guess. Split load units with 1, 2 , and 3rcd with installer using best practical options most of the time to choose which way to go. options that include installing stair lighting based on nothing other than the age of the current owner and the latest amendment to fall through his door. installing a non rcd circuit to the boiler room for a audible, wired-up EN 50291 monoxide alarms that may or may not be installed in years to come "future proof". its a real joke check out the amount of amendments in the 17th edition regs. who could forget the changes the 16th edition made for plumbers with having to cross bond all pipework in bathrooms and with trv to be fitted as standard had to cross bond between the pipe and the rad.(looked great in a £20.000 bathroom ) especially that we had to buy the earth clamps with the blue safety tag due to it being classed as a damp environment. then having to run a 6mm earth back to the consumer unit and a separate 10mm earth and 10mm t+e if you were fitting a electrical shower.this all happening while the electrician was cross bonding bathroom lighting circuits back to the switch then back to the box leaving a nice yellow warning sticker on the new lighting just installed. All regulations back in 2005 now scraped or amended. £4000 Hips and chaps certificates you needed just to sell your house... all scrapped. part p 2005 competent person definition changed 2013 to save Electrical Safety Council £61.3million and a promise from the government to look into placing health warning stickers on all diy sold electrical sockets.
i know i went a little long winded in replying to your post regarding, part l existing dwellings. but with all the blunders and all the changes made to building regs since 2005, The ongoing fight between the gas safety trust and the Electrical Safety Council over rights to control Part J of the Building Regulations. the overlap between the HSE and Department for Communities and Local Government over the safety of local Building Control, through in "gas safe" supposable looking after the register of approved fitters of the registered competent persons officially 32% of fitters do not comply with part p have been tarnished with not knowing what forms are to be filled in for local building control. when you look at all the bureaucracy electricians and heating engineers have to deal with i'm surprised its not higher.
