I am starting to plan the plumbing for our new house. I know that for the hot water pipes I need to put as much insulation on as possible but, for the cold water pipes, the issue is more about stopping condensation on the pipes. I will probably be using something like Climaflex for the pipe insulation. Can anybody give me any guidance on what thickness of insulation I would need on a 15mm plastic pipe to avoid condensation. (Assuming pipes running through heated enevelope of airtight, mechanically ventilated house.)

Thanks
AA

Hi Tony, It will be an unvented system, so no tank in the loft. I wasn't going to insulate any of the heating pipes, but I was assuming that I would get a more constant hot water supply out of the taps (after the initial wait), if I insulated the hot water pipes (e.g. repeated use of the hot tap at the kitchen sink).

I think there is some value in insulating HW pipes along well used short runs (definately necessary close to tank area) But more so in using smaller bore pipe were a lower flow rate is sufficient and designing run to be as short as possible. Check out the AECB water standards for some guidance of flow rates etc.