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Discuss Where to position CH pipes under groundfloor suspended floor in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

bwt

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5
I am about to insulate a suspended timber groundfloor in a 1930s semi. The joists are 2"x5" with about 400mm of air space below. The pipes currently run below the floor, and the pipework is a mess, with very little insulation. As I need to reroute pipes anyway, am I best running them between the joists, within the new floor insulation or keep them under the floor but obviously insulate them. The pipes will be running perpendicular to the joists, so I would need to drill holes in the joists.
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
Messages
28,508
Solutions
1
Notch them in the top of the joist just enough for the pipes plus a felt wrap

as you wouldn’t be able to bend the copper enough to get them in the holes
 

Ben-gee

Esteemed
Plumber
Messages
2,059
What spans have you got, 5 x 2 is pretty small?
Measure your spans and it might be that if you’re close to limits I would put them back under the floor to avoid drilling/notching.
 

bwt

Messages
5
Are you using copper or plastic?
The existing is a length of copper connected to plastic where someone has moved the radiator previously. I will probably replace with plastic as it results in less joints to cause problems later.
 

Ric2013

Plumber
Messages
3,230
You could probably also just about pull soft copper through drilled joists or (as I do) joint normal copper tube between every joist.

A soldered joint in copper is very unlikely indeed to require any further attention after it has been installed correctly. You are right, however, not to want to have hidden compression joints.

Plastic, installed correctly, could also be a good bet. If you can have any joints accessible (ideally above the floor) that would be good, but, in practice, plastic joints, installed correctly (read the instructions) have tended to be generally reliable.
 
Messages
2
Notching is not the best of solution unless you absolutely have to. Notching leaves you exposed to any nail or screw to be drilled into the pipe. Drilling in the middle or as close to the middle of a 2x4 ensures that the 1 1/4 drywall screw/nail will not penetrate, especially if somebody else is drywalling for you. Notching will also weaken the 2x4, making its strength as little as a 2x2.

Copper pipe tubing is pretty flexible when putting it through the 2x4's as long as the holes line up within reason. The tubing doesn't have to be perfectly straight, but you do not want to kink it either. You should be able to put 12' lengths with a little bit of pre-planning.
 

Ric2013

Plumber
Messages
3,230
Copper pipe tubing is pretty flexible when putting it through the 2x4's as long as the holes line up within reason. The tubing doesn't have to be perfectly straight, but you do not want to kink it either. You should be able to put 12' lengths with a little bit of pre-planning.
Ah. You see, here is where being an international forum has its downside.

If I am correct in assuming that the OP is in the UK, then standard copper tube will be half-hard/Table X/R250 and you simply won't find it is 'fairly flexible' at all: as you say, you don't want to kink it, and Table X copper kinks almost immediately unless it's in a pipe bender. If, on the other hand, the OP is American, standard copper might be soft copper and, if so, what you say may wll be true.

It depends, of course also what diameter these proposed pipes are!
 

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