Hi there,

 

I'm biting the bullet and putting a new insulated slab in the ground floor of a renovation project. I've finished the main soil runs and they're bedded in pea gravel waiting for the sub-base to go on top. I also need to run a cold water feed from the main supply to the other side of the property. 

 

Should that be run in the sub-base or on the warm side of the insulation? My proposed build-up is actually sub-base 100mm, PIR, UFH pipes and 100mm of concrete over the top so if the cold water pipe goes on the warm side of the insulation it'll be within the slab that's acting as my thermal mass, which doesn't seem correct. 

 

If it's meant to be run through the sub base, what pipe would be correct to use for that, and does it need to be in conduit?

 

Cheers,

Maz

You want the cold mains in the ground, ideally, so you get cold water to draw off for drinking etc.

 

If there’s a chance the pipe would routinely sit over 20°c then legionella is a concern.

 

That’s why pipes are required to be buried low, > 600mm, not just to stop them being damaged. 
 

Where the sub base is it may still have sharp stone, so duct it and pull the pipe through afterwards afaic. 

13 minutes ago, Nickfromwales said:

Where the sub base is it may still have sharp stone, so duct it and pull the pipe through afterwards afaic. 

 

Thanks, ducting it makes sense then. What kind of ducting is suitable for this purpose? A builder told me to use 32mm waste pipe but there's no way I can get my 22mm plastic pipe through that.

5 minutes ago, maznaz said:

22mm plastic pipe through that

What are using if 22mm is bigger than 32mm waste pipe?

 

All my cold pipes are are under the insulation in ducts, works well

13 minutes ago, maznaz said:

A builder told me to use 32mm waste pipe

if it is going in an open trench then you can lay it is sand and no duct.

 

If pulling through later then you need a great big expensive duct, because the water pipe likes to bend, so this is best avoided.

11 minutes ago, JohnMo said:

What are using if 22mm is bigger than 32mm waste pipe?

 

The problem I encountered was the 22mm plastic water pipe wouldn't negotiate the bends in the 32mm waste pipe without kinking. It was perfectly fine in the straight run of course but needs a 90 at each end to run up the wall to the main house.

Run in conduit then instead of you have a change of direction or just do a straight A to B to keep it simple

2 hours ago, saveasteading said:

if it is going in an open trench then you can lay it is sand and no duct.

 

thanks, I'll ask the BCO about this option as it would definitely be easiest

4 hours ago, maznaz said:

I also need to run a cold water feed from the main supply to the other side of the property. 

 

3 hours ago, maznaz said:

The problem I encountered was the 22mm plastic water pipe wouldn't negotiate the bends in the 32mm waste pipe without kinking. It was perfectly fine in the straight run of course but needs a 90 at each end to run up the wall to the main house.

You're not allowed to use anything other than the rated MDPE (blue) water pipe, which is 20 / 25 / 32mm for a rising cold mains. 22mm would give a lot of restriction most likely too. Is this a mains or a T off the mains?

 

https://www.toolstation.com/mdpe-pipe/p31388?store=W8&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&gad_source=1&gad_campaignid=17808462181&gbraid=0AAAAAD-vLcU0T7r6bZ8njV1OqqMbxcGaz&gclid=CjwKCAjwk7DFBhBAEiwAeYbJsYqd05h9aKi4J4x3GAK2rKrNEyPpEW_WvIQhJtcylKLpeYwK9yopIRoCqMMQAvD_BwE

10 hours ago, Nickfromwales said:

Is this a mains or a T off the mains?

Thanks for that. It’s blue mdpe into the house, then into 22mm copper and a15mm copper tee is what we’re needing to pass under the slab. Should that transition back into mdpe then?

I've used left over 75mm MVHR ducting for ducting some services in my garage. 

 

Would this suit? 

Personally, under the slab I wouldnt run copper, i guess many have done in the past though, Me, I'd run a 110mm soil pipe and push 25mm mdpe through it, rest bend where it comes back out of the slab.  No pipe joints where you cant get to them.

This what I did. Ran mains water pipe mdpe to stop cock. Then converted to 22mm copper and to a cold water manifold. Then from manifold went below floor insulation running 15mm Hep2O in conduit to each room that needed cold water. All joints above ground, ample flow to each room. In theory replaceable, to comply with an obscure rule I found in building regs. You then have a central isolation point for each room that should be easily accessible. Allows each room to be commissioned at different times, and if you get a leak you can just isolate that room while it gets repaired.

9 hours ago, maznaz said:

Thanks for that. It’s blue mdpe into the house, then into 22mm copper and a15mm copper tee is what we’re needing to pass under the slab. Should that transition back into mdpe then?

I would. That pipe is designed to be directly buried forever and is pretty bombproof.

 

If it is off a T after the primary stopcock it is no longer 'technically' a rising cold mains, it's just a spur, so no need to do the stopcock and non return valve etc all over again.

7 hours ago, Iceverge said:

I've used left over 75mm MVHR ducting for ducting some services in my garage. 

 

Would this suit? 

Can't see why not as long as the bends you form are long-radius.