Central Heating Pipes in Concrete Slab (or should I go for a screed on top of the slab?)

[WoOt]

I was planning to dig down my oversite to 400mm below DPC level, and doing what looked like a fairly standard floor:

• 150mm type 1 (compacted)
• 50mm sharp sand (compacted)
• 1200 gauge DPM
• 100mm Celotex
• 1200 gauge DPM
  
• 100mm C20 Concrete

I'm now trying to figure out how to feed my radiators in the extension. Initial plan was to run Push-Fit Polybutylene Barrier Pipe in the 100mm slab, but I wonder whether a 100mm slab is thick enough to do this, or whether I'd be creating weak points?

Is this possible? Is the slab thick enough? Do I require some type of conduit to run the barrier pipe through?

Or would it be wiser to go for some sort of screed after the concrete is down? I've only ever done 2 shed/garage concrete floors, so I'm not that confident that I'd be able to get the slab 100% level and at the exact same height as the existing internal floor.

Any DIY suggestions and help appreciated.

 

[cdbe]

You don't need second DPM, just tape the joints of the celotex. You'll need to flatten out the pipes and tape them down as they like to float up:

The conventional way is to finish with a screed on top but you can use a slab if you work out the finished floor level accurately and you level accurately. I got mine to within 10mm over 30m² (and that's mainly a dip in one corner) which a bit of self leveling will sort out. Saves the cost of a screed and digging out more muck.

 

[WoOt]

Thank you @cdbe , so you didn't run those in any conduit? Did you put any mesh down on top of that?

 

[Notch7]

Most builders I know do concrete slab first, then get plumber to run pipes.

one tip if you do that: do the celetex in 2 layers of 50mm: lay the first and cut around the pipes, then lay second layer in opposite direction.

When I built orangeries I got the electricians to run their cables all around the perimeter, tight to the inner blockwork -that way it was much easier to to lay the celetex.


obviously you can put down insulation below the concrete oversite -although that means there is a bigger mass on the warm side -theres good and bad in that

 

[cdbe]

Thank you @cdbe , so you didn't run those in any conduit? Did you put any mesh down on top of that?

No mesh, no conduit. As per notch it is a big slab on the warm side but we're having a wood burner so it will be a good heat store for us.

 

[WoOt]

Thank you. Already bought the 100mm insulation. But I like @cdbe 's method so will go for that. Slab is 11m by 3.5m so I think I might need some mesh too. More research required.

Big day tomorrow. We dug footings to 800mm today and found a lot of flint in the clay. So much so, we can't get through with the digger. Let's hope Building Control-guy is in a good mood tomorrow and allows us to leave it at that. If not, the digger driver fears we'll still be digging this time next week.