Posted By: djhPlastic is less likely to leak than copper since there will be fewer joints in inaccessible places. It should be pressure tested before being hidden away. You could always run it inside a larger diameter pipe if you're particularly concerned (like electrical cable in conduit). I would run it in the insulation, since you'd need to insulate it otherwise.

Posted By: WillInAberdeenIf the pipes run parallel to the direction of the joists, it's convenient to run them between the joists, within the insulation layer but not too deep, so the residual heat losses end up in the room. I used pipe insulation as well as burying them in the wool insulation layer, as I felt the wool didn't "wrap around" the pipe very well.

But for pipes going perpendicular to the joists, I think it is easier to go underneath the joists, rather than thread through holes in the joists.

You can get metal pushfit fittings, which fit both copper and pastic pipe.

Mice just love to shred the standard clip-on polyethylene foam pipe insulation, must make for comfy nesting. I'm using some foil-covered rockwool pipe insulation in the hope that it's not so comfortable.

Posted By: Peter_in_Hungary

Posted By: GreenPaddyJust consider mice. They are very fond of

all things organic - along with other bugs etc. I would be a bit nervous about putting sheeps wool as insulation between joists.

Re pipe work - have you considered alpex pipe?

Posted By: Peter_in_Hungary

Posted By: bardoThe alpex pip sounds interesting. Have you used it? What are the merits?

I have used alpex, I found it good, the 5 layer alpex has an O2 barrier, useful on closed systems. It is reasonably easy to install and can be got pre-insulated. The joints are either swaged (install all the pipework then hire the machine for a day) or bolt-up. The fittings tend to be more expensive than copper but you use a lot less of them and with a bit of planning you can avoid fittings in hidden places (like underfloor). Alpex pipe is good for drinking water as well as CH.

I have also installed a CH system using 6mm nylon microbore - very easy but benefits from a centrally placed boiler as each radiator had its dedicated supply and return from the manifolds. Although microbore seems to have gone out of fashion these days.

There are a couple of threads on here about using sheeps wool insulation under floor - probably worth a read if you haven't already done so.

Posted By: bxmanShould there be a need for central heating these days ?

Posted By: revorI would avoid any joints that eventually become inaccessible. Could be trouble in years to come. A lot will depend on your finished floor covering and whether you will in the future be able to lift it and gain access. Are you already committed to I joists? I used web based joists "posi joist" and they are just great to run pipes through.

I used plastic pipe under floor and connected to copper with brass compression fittings elsewhere for domestic supply. (Also had to comply with my insurance company as I had to agree to no hot work so no soldering and the crimping gear was too expensive) Compression joints are a great benefit if later you want to modify the plumbing.

Given the void under the joists I presume this will be ventilated to avoid damp issues in which case pipes will need to be well insulated.

I used alpex for underfloor heating and I would consider this for conventional CH system. It is easy to bend and retains the shape so you are not fighting it like you would do with barrier pipe. It also comes in very long coils mine were 360 m long so less wasteful. If you use it there are different diameters around the 15 mm size mine was 16 mm and if you want to connect up to 15 mm you will need conversion fittings. So be aware.

If you are planning on soil pipe or ducting to go under the floor they may need to go in when you fit the joists.

Have not used sheep's wool insulation but I looked at it and considered it to be too expensive. Also been horror stories about it getting moth eaten if it's not been manufactured properly.

Posted By: Peter_in_Hungary

Posted By: bardoI am interested in alpex however can't see the real merit over plastic especially given that we will need to adapt to fit onto copper pipes coming out the floor and into small radiators.

The alpex installation I did had the alpex pipe coming out of the floor and going straight to the radiators without conversion to copper. If the rad. is the normal height from the floor there are no problems, long(ish) horizontal runs in alpex can develop a sag over time and would be more vulnerable to knocks

I see you are using a plumber rather than DIY. IMO there is a lot of merit in going with what ever is in the middle of your plumbers comfort zone. If what your plumber is happy using is too far away from what you want - then better to get a different plumber!

Posted By: bardowhat is your experience in obtaining fittings for Alpex and or converting to 15mm?