I am building a new office next to the house; it is about 1.5m away. I need to run, from the house's upstairs bathroom, 1 hot, 1 cold, and radiator with return (all of which I believe are 28mm to the bathroom).
They need to come down the outside wall (2.5m ish), under the path (1.5m ish) and then back up to the office (0.5m ish). My problem is making sure they are both insulated for heat lose and frost damage (south of England, -5°C is about the worst).
I was going to go out of the bathroom into a pipe (something like a 110mm waste); in this pipe I was going to use pieces of wood to brace the pipes in the middle of the pipe (think of a large button that would wedge itself in the waste pipe and the water pipes run through the thread holes).
I was going to use some kind of plastic pipe (what is best?). I was also going to wrap rubber or foam around each pipe, and to top it off, fill the voids of the "waste" pipe with foam chips or beads.
In case of upcoming long nasty periods and the building not being in use, I was going to put stop valves (with stop and "bridging" valves for radiators) in the house bathroom and then draining valves in the office. In fact, I'm not sure I will ever do this as I do not want to do the massive bleeding task after, probably easier just to keep on low heat all winter.
Does this sound like a viable idea? Has anyone done something similar or have another (better) solution?
I enjoy plumbing but I am in no way trained, so…