not all houses are suited to it, i've looked at a few for feasibility and they are either too small, or roof too shallow, or too much structural work required, or losing a small bedroom to fit in a stair meaning gaining a crap-sized loft room wouldnt be worth it.

most can be converted though. as long as its not a flat-roofed house haha

also i've had to do a few plans for people to get retrospective building regs where they've had builders who didnt tell them about regs, and its a real PITA to put them right usually!