Foul waste through insulation layer

[JohnMartin68]

What is the best way to support and protect a 110mm foul waste pipe if it needs to run horizontally through floor insulation? See  attached sketch. The elevations cannot be changed for various reasons. I was thinking of cutting a rough channel through the insulation and filling it expanding foam with the pipe in place, instead of pea gravel. Or should it just be pea gravel (this will probably cause heat leakage)?

[saveasteading]

Pea gravel.. it is more important to lay the drain to be stable and run efficiently than the small heat loss. The air gaps in the gravel will add some insulation. The air in the pipe is the main loss of insulation and can't be prevented.

Gravel up to the top of the pipe, then lay what eps you can over it.

 

I wonder what insulation pea gravel provides. 30% or so air pockets, and lots of very tiny gravel to gravel contact. Much better than sand.

[JohnMartin68]

Thanks you're probably correct the gravel will provide a bit of insulation. I just wasn't sure if the reasons for using pea gravel to support the pipe were still valid in a channel carved out of EPS instead of a trench dug in the earth. For one thing there must be precaution taken that the gravel won't 'leak' from gaps in the insulation but then if the insulation is laid properly without any voids this shouldn't happen.

[Russell griffiths]

Does the pipe need to be that high. 
it should rally be down in the soil or hardcore layer

will your height outside allow you to drop it below the insulation. 

[saveasteading]

28 minutes ago, JohnMartin68 said:

precaution taken that the gravel won't 'leak' from gaps in the insulation

That attention to detail will ensure that you deal with it as you progress.

Perhaps slightly lean on the gravel that lies under the pipe, to press it into any gaps.

[JohnMartin68]

17 minutes ago, Russell griffiths said:

Will your height outside allow you to drop it below the insulation. 

Not without lowering an unknown but at least 10m length of existing pipe.

[JohnMartin68]

Out of interest what is the reason for insisting on gravel instead of using for example foam? Is it just for compliance with what BC expect to see? For obvious reasons foam wouldn't work in an unlined earth trench but the insulation shouldn't move significantly when its in place.

[saveasteading]

Foam isn't very controllable. You would have to position the pipe very precisely, on supports and load it down. Then squirt foam slowly so that it doesn't force the pipe up as if expands. Check the pipe all the while. And repeat.

How would you prop the pipe? Not on anything hard, so gravel at intervals.

 

There will be plenty of instances of people using crumbled pir, or expanding foam. Mostly it works,  presumably. But perfection is worthwhile.

[Conor]

use a proper rest bend with foot and a SINGLE length of pipe going to the outside and set both ends in a little concrete. Then pack in around with insulation and foam. Put the pipe in before the insulation.

 

BTW, 150mm EPS doesn't seem like very much to me. What grade is it? In an insulated raft you'd normally have 200-300mm

[JohnMartin68]

22 minutes ago, Conor said:

BTW, 150mm EPS doesn't seem like very much to me. What grade is it? In an insulated raft you'd normally have 200-300mm

Retrofit, there wasn't room for any more without digging below the top of the footing. Single room, small area that needed to be dug up anyway. 150mm vs 300mm won't make a huge difference to total annual running costs even assuming UFH is left on 24/7. The compressive grade is either 100 or 150. It's the premium version which is darker and supposed to have a slightly better U value than standard.