I'm doing a house renovation, and the hot&cold water feeds to the showers in the bathroom and ensuite are in 15mm copper. I want to upgrade to 22mm where possible to get better flow, as the hot water is from a cylinder with header tank.
My view is that I'd rather install 22mm everwhere where it won't be easy to replace later, like underneath tiled floors, and behind tiled walls. There will still be some runs in 15mm (or maybe half inch, as some of the pipework is very old), but I might replace these eventually.
Is this a reasonable thing to do? Are there any reasons why I shouldn't install 22mm where possible (apart from cost, which is not a huge factor when looking at the whole job)?