Shallow drains - problem?

[G and J]

  On 03/03/2025 at 10:19, Roger440 said:

 

In which case, given your other challenges seems like a no brainer to me.

 

 

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I am one with special needs lol

 

So now I’m thinking 120-150mm slab on 300mm of EPS with all drains completely within the EPS.  Don’t yet know where the DPM goes, don’t know if I convert to bnb for the back half of the house as the ground falls away and there’s no drains, don’t know how I support the poo pipes, but hey, a ‘don’t know’ shopping list is a start.  

[Nickfromwales]

  On 03/03/2025 at 10:22, G and J said:

I am one with special needs lol

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Get in line pal.   

 

  On 03/03/2025 at 10:22, G and J said:

I am one with special needs lol

 

So now I’m thinking 120-150mm slab on 300mm of EPS with all drains completely within the EPS.  Don’t yet know where the DPM goes, don’t know if I convert to bnb for the back half of the house as the ground falls away and there’s no drains, don’t know how I support the poo pipes, but hey, a ‘don’t know’ shopping list is a start.  

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DPM goes over the lowest layer of EPS, so it’s using the bottom sheet of insulation as a sacrificial protector to keep it intact.

[G and J]

  On 03/03/2025 at 10:23, Nickfromwales said:

DPM goes over the lowest layer of EPS, so it’s using the bottom sheet of insulation as a sacrificial protector to keep it intact.

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So the drains sit in the EPS layer above the DPM.

 

Presumably one tapes up the penetrations and it’s all ok cos my plumbing is good enough to ensure no leaks.  

[saveasteading]

The sand blinding is only for level control, as stone is tricky to get level and smooth. It shouldn't be thick.

The dpm goes on that.

A slab on that is unnecessary structurally but gives control....ie it is hard and doesn't get displaced or the dpm get torn.. But it can be a thinnish screed. In this case you might reduce the hardcore equivalently.

[G and J]

  On 03/03/2025 at 18:51, saveasteading said:

The sand blinding is only for level control, as stome is tricky to get level and smooth. It shouldn't be thick.

The dpm goes on that.

A slab on that is unnecessary structurally but gives control....ie it is hard and doesn't get displaced or the dpm get torn.. But it can be a thinnish screed. In this case you might reduce the hardcore equivalently.

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And presumably as long as it is of even thickness I can put a lot of EPS down there. 

[Nickfromwales]

  On 03/03/2025 at 23:57, G and J said:

And presumably as long as it is of even thickness I can put a lot of EPS down there. 

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Yup.  I always recommend a sacrificial layer of EPS before membrane, even if you do just a 25mm layer, then DPM, then carry on with the rest of the EPS / PIR.

PIR can be thinner for the equivalent value compared to EPS, so 200mm of EPS can be replaced by prob 175mm of PIR in reality, number can be crunched but you’re not going to be far off ‘great’ with 25mm EPS, then 75mm PIR then 100mm PIR, or 2x 100 of EPS over the 25mm layer. 
Just work out costs and logistics for the extra excavation and muck away, as 25mm saving over a large area soon adds up.

[saveasteading]

Pir  0.022   eps 0.037

 

PIR provides  significantly better insulation, close to double, but similarly more expensive: close to double

 

I'm gradually coming round to 100mm EPS under 100mm PIR as optimum, with joints staggered. Or see what the market is doing at the time.

This because if diminishing returns with depth.

 

@Nickfromwalesplease explain your sacrificial idea? Is this straight on the blinding?

Sacrificial meaning some will be damaged and replaced? Or squashed into protruding  stones?

[Nickfromwales]

  On 04/03/2025 at 08:53, saveasteading said:

Pir  0.022   eps 0.037

 

PIR provides  significantly better insulation, close to double, but similarly more expensive: close to double

 

I'm gradually coming round to 100mm EPS under 100mm PIR as optimum, with joints staggered. Or see what the market is doing at the time.

This because if diminishing returns with depth.

 

@Nickfromwalesplease explain your sacrificial idea? Is this straight on the blinding?

Sacrificial meaning some will be damaged and replaced? Or squashed into protruding  stones?

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I’m just not a fan of putting the ‘fragile’ membrane down on terra firma so makes sense to me to split the lower layer of insulation 25/75 and put the membrane ‘out of harms reach’ so to speak. 
If any sharps etc stab into the underlying EPS then that’s of zero consequence. 
 

25+75/100 EPS then you could even do a second membrane to start reinforcing AT, then PIR on top of that is plenty good enough afaic.

 

Diminishing returns are into rows of zeros after the decimal place then in all reality. At some stage you need to just live and get on, vs micromanage every nth degree. Too many people take too long NOT living in their dream home to save £1000 over 10 years and so on….which is 2 days part time work per annum btw. 

[saveasteading]

  On 04/03/2025 at 09:26, Nickfromwales said:

get on, vs micromanage

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Agreed. And not enough attention* is given to the insulation from the ground beneath the floor. In a chunky house, a lot of the floor is far from the cold outside world. 

 

* the manufacturers choose not to tell us.

[Nickfromwales]

  On 04/03/2025 at 09:39, saveasteading said:

Agreed. And not enough attention* is given to the insulation from the ground beneath the floor. In a chunky house, a lot of the floor is far from the cold outside world. 

 

* the manufacturers choose not to tell us.

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Yup. Just needs the ‘right amount of attention’ and then go CRAZY on air tightness. You could have 1000mm of insulation in the walls / roof but still have a cold house in winter if the infiltration is high.

If someone competent says they can whack the sub base very near to ‘flat and level’, meaning you only need to put just the minimum thickness (<20mm) sand blinding down, then replacing the 25mm deficit with EPS would always be my choice.
 

That’s better than someone importing and laying a full 50mm sand blinding layer down, which is cold, and is only doing only one job.

 

Cheaper and easier to throw some 8x4’s of EPS in there, and then the primary DPM, (you can choose to the do another thinner ‘secondary’ membrane further up in the insulation layer and start your fundamental AT mitigations there).

[G and J]

  On 04/03/2025 at 09:49, Nickfromwales said:

Yup. Just needs the ‘right amount of attention’ and then go CRAZY on air tightness. You could have 1000mm of insulation in the walls / roof but still have a cold house in winter if the infiltration is high.

 

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Thank you - and Amen to the airtightness.

 

 

I really appreciate all this guys.

 

I want to explore this debate re what goes under the insulation.  Before that I want to check understanding and put the drains issue to bed.

 

Whatever goes under the insulation my poo pipes are going in the insulation and above my main DPM, assuming my BCO is happy with that.

 

That means I can have a 100mm screed plus UFH or 120/150mm construction slab with UFH.  Good news.

 

I just have to have enough insulation to house the pipes allowing for their falls.  I'm thinking I can use the insulation to carefully manage the falls to make sure I've got no low spots due to pipe deformation, so safe to use long lengths of plastic, if needed rotated to make sure any bend in the pipe is horizontal and not vertical and thus does not affect the falls.

 

Is all that correct?

 

[Russell griffiths]

Don’t buy 6m lengths of pipe, they always have a significant bend in them, ok if going in a trench you can pack them straight, but trying to hold them in place in your situation would be a pain. 

[Nickfromwales]

  On 04/03/2025 at 12:02, Russell griffiths said:

Don’t buy 6m lengths of pipe, they always have a significant bend in them, ok if going in a trench you can pack them straight, but trying to hold them in place in your situation would be a pain. 

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Rebar and concrete pads? Will need something regardless to hold these in place robustly whilst working the insulation into place around these.

[G and J]

  On 04/03/2025 at 13:14, Nickfromwales said:

Rebar and concrete pads? Will need something regardless to hold these in place robustly whilst working the insulation into place around these.

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Laterally, vertically, or both?

[saveasteading]

  On 04/03/2025 at 13:33, G and J said:

Laterally, vertically, or both?

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The pipes have start and finish location. Between it doesn't matter if it turns slightly laterally.

For falls though, don't adjust by insulation. Lay the pipe to grade using either a level. A spirit level with packers on one end.  Then fix solid on dots and dabs, and perhaps a weight on top. 

Check by eye.

Insulation then fits around this arrangement.

[Nickfromwales]

  On 04/03/2025 at 13:33, G and J said:

Laterally, vertically, or both?

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The start and finish points are relatively easy to fix and lock in, it's the deflection along the run that needs a bit of thought, especially as you'll be bumping into these, stepping over, and accidentally kicking them and what not.

 

Depending on ground conditions, in the past I have just sharpened a bit of 2x1 (4-500mm long) and then put a 100mm cross piece on top to make a T shaped chair and then simply smacked these into the ground at diminishing heights for the fall, say 8-900mm apart. Use a string line from invert to invert as a guide and then hammer these into the ground to suit. Lay the pipe on top and lash it down to these chairs so they cant move about. Job done. Have the 1st fitting and the last fitting in place, and go point to point with the string and then chairs.

 

BCO will want to see rest bends with concrete wellies, as per bb regs, same with chambers, but also good to concrete pad around any changes in direction. FYI, you should not have any changes in direction underground where there are any form of solids, unless you can rod from both direction to that change point.

 

I'd say to use the long 5-6m lengths to avoid joints, but whatever you find easiest tbh. Don't fear using joints, these things are piss-easy to make off, and are bombproof when underground (that's where they're designed to be forever at the end of the day).

[dpmiller]

and if you're going EPS, make it the graphite stuff, substantially better for minimal extra cost.

[G and J]

  On 04/03/2025 at 16:00, Nickfromwales said:

FYI, you should not have any changes in direction underground where there are any form of solids, unless you can rod from both direction to that change point.

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Is that still true of a single easy bend?

[G and J]

  On 04/03/2025 at 15:23, saveasteading said:

The pipes have start and finish location. Between it doesn't matter if it turns slightly laterally.

For falls though, don't adjust by insulation. Lay the pipe to grade using either a level. A spirit level with packers on one end.  Then fix solid on dots and dabs, and perhaps a weight on top. 

Check by eye.

Insulation then fits around this arrangement.

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Noted. Thank you. 

[G and J]

  On 04/03/2025 at 16:00, Nickfromwales said:

Depending on ground conditions, in the past I have just sharpened a bit of 2x1 (4-500mm long) and then put a 100mm cross piece on top to make a T shaped chair and then simply smacked these into the ground at diminishing heights for the fall, say 8-900mm apart. Use a string line from invert to invert as a guide and then hammer these into the ground to suit. Lay the pipe on top and lash it down to these chairs so they cant move about. Job done. Have the 1st fitting and the last fitting in place, and go point to point with the string and then chairs.

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Very good plan. Again, thank you. 

[G and J]

  On 04/03/2025 at 22:02, dpmiller said:

and if you're going EPS, make it the graphite stuff, substantially better for minimal extra cost.

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Interesting.  Will research.