Supply to shower in my Loft

[kayakand]

I am about to install a shower room on the recently converted loft shell of my Victorian terraced two bedroom property. Converted to four beds. The mains supply to the house is lead to the threshold and has a temporary 15mm plastic run to one tap. The lead bore is around 15mm or less and the mains pressure I am told is pretty good. (not sure on the flow rate however around the 11 ltr + mark)

There is no central heating system or hot and cold supply in the house therefore I have a clean sheet. I will be getting a suitable combi installed for the job. I am not able to upgrade the supply to the house due to the horrendous cost from Thames Water.

My two questions are;
1. Would you suggest I should upgrade my supply from the lead to feed the boiler and hot and cold supply to 25mm plastic? I have been advised not to bother.
2. Should I run 22mm copper to feed the 1st floor bathroom and 2nd floor shower room from the boiler/mains? Or should I run 15mm and use reduces to adapt the shower regulator and bath taps?

Much appreciate any comments or ideas you may have.
Thanks

 

[Newboy]

before you do anything I'd check what static/dynamic pressure and flow rates are. Given that the pressure in some parts of London can struggle to give you any meaningful flow rates at third floor level it makes sense to see what you have available before committing to anything at this stage.

I'd be inclined to check all your measurements at peak demand times - the pressure/flow can drop significantly when all the neighbours are drawing water from old mains.