I will be getting a mate who is a gas certified installer to run a new gas pipe for a range cooker from my garage (where the gas mains is) through a couple of internal walls and under the suspended timber floors to my new kitchen. He is doing it as a favour so I am trying to make the job as simple as possible for him to reduce his time on the job. I will be buying all the materials and removing floorboards and drilling through the walls. I have two questions. 1. What material and diameter of pipe should I be buying. 2. Should the pipe go through joists or can it be hung from them? I can see it being much easier for him to do the job if they are hung under the joists but I need them to comply to any regulations.