Infill max depth under concrete floor

[cwr]

I have on my drawings the following make up of the ground floor:

 

screed

insulation 170mm

Concrete 150mm

sand blinding 50mm

DPM

Type 1/hardcore compacted min 150mm, max 600mm

 

I understand that there should be 600mm max infill. So does that include the 50mm of sand blinding? ie should Type 1/hardcore be max 550mm?

 

Reason for asking is because top of founds to underside of slab goes as high as 950mm, so trying to work out how much lean mix concrete would be needed to back fill trenches.This being one of the structural engineers suggestions, and I suspect the cheapest.

Cheers,

 

 

 

 

[tonyshouse]

Sand blinding is dangerous , it can later percolate into the hardcore leaving a void 

 

I like insulation under the concrete = greater comfort, slower temperature swings and the more the merrier with insulation 

[Onoff]

Lots of people on here with sand blinding with seemingly no issues (including me). Sharp sand in my case. 

 

Agree with having the concrete above the insulation. I just have dead level concrete above my insulation so no screed. UFH pipe about 1/3 of the way up in 100mm concrete. Tiles straight onto the concrete. Nice big heat store is the idea.

 

 

[Onoff]

Is this a floating slab new build, a refurb, what? No way you can get more insulation in?

 

I said only the other day (yet again ?) @Jeremy Harris has 300mm of EPS under his slab and still estimated 8% heat loss downward!

[cwr]

 

Quote

Sand blinding is dangerous , it can later percolate into the hardcore leaving a void 

In fairness the builders already have fine stone on site rather than sand. 

 

Quote

Is this a floating slab new build, a refurb, what? No way you can get more insulation in?

Yes floating slab for new build.

 

So far the footings have been built to top level of slab, as per sketch below. I like the idea of more insulation as its adding something that will have more useful purpose. Only thing is to do that would mean slab top level to lower then where the footings now are so maybe not the easiest to level the slab?

 

Proposal with lean mix concrete something like this. Think I'll need about 11m3:

 

[Russell griffiths]

Are you on a slope, why such a high build up or such a deep footings. 

[cwr]

Yeah a slight slope, about 1m from one end to the other. I wanted to dig in a bit more at the top end but the founds got poured...

[Russell griffiths]

So swap out your insulation for cheaper EPS and use more of it, 250 or 300mm eps will probably be cheaper and gains your height needed. 

Buy it direct from the manufacturer and not a merchant. 

[OldSpot]

Lots on here have done away with a screed and just have a floor build up as shown in your second post with the floor finish going straight on the concrete slab.

If you swapped out some of the hardcore - with 300mm of EPS100 - you'll end up with nominally 1mm of compression. This is based on normal domestic loading of the floor. You'll also get a well insulated floor to boot!

Approx. 2/3rds of the compression will be when your (150mm) concrete slab goes down so in reality you'll end up with a "variable" compression of ~ 0.3mm or naff all.

I say variable because it will be due to the load imposed by the furniture/people etc living in the property.

[Onoff]

Existing room, I did:

 

Tiles

100mm wet concrete (laid with screed rails)

Poly Panels with 16mm UFH pipes

150mm pir (in two layers)

DPM

25mm eps

Sand (sharp) blind 

Type2

 

 

It feels like a floor should! ?

[cwr]

Thank you for the suggestions, have sent some ideas to SE and was hoping to get a response by now but he's been busy on other site visits so will now be after the weekend.

I originally favoured slab on top of insulation, tho can't for the life or me remember why I moved away from it. Someone somehow convinced me to do so.

Stone blinding already laid at the other end of the build, so need to consider a way forwards that either integrates with original plan or does not require excessive re-work.