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[noseall]

Why will the insulation be soaking wet just because it is below the slab? It is still above the DPM.

Are you telling me that you are in the construction industry and you gave never come across the detail?

Very strange.

 

[Donnapaddy]

Van you not be rude .if your not giving advice please no more comments .it's my thread for gods sake

 

[cAtLeYx]

Why will the insulation be soaking wet just because it is below the slab? It is still above the DPM.

Because you've installed it below the ground bearing slab before you have constructed the super-structure, roof etc and its now pouring down with rain - This this the whole reason why the method and sequence of works is incorrect. Re-read the the origin post and ask the same question.

Are you telling me that you are in the construction industry and you gave never come across the detail?

Yes, I came across this detail at university in some old construction technology books. Things really have moved on. Hopefully you can understand the alternative method of ground floor construction and understand why the method being used by the OP's building really will cause issues.

Ask yourself one question and be honest - If you were constructing your own extension which construction method would you use..

 

[cAtLeYx]

Van you not be rude .if your not giving advice please no more comments .it's my thread for gods sake

Hi - Yes agree you came her for advice. As your builder has already commenced construction of your extension, and has installed the VCL & insulation below the concrete slab, you now have a swimming pool with no way of water escaping and purely relying on evaporation once the building is watertight and heated. Hopefully someone on this forum can advise on what is now required.

 

[noseall]

Ask yourself one question and be honest - If you were constructing your own extension which construction method would you use..

UFH - above the slab.
Otherwise below. Having the mass of the concrete above has benefits. The same as having the insulation in the cavity as opposed to the inner surface if the walls.

 

[cAtLeYx]

UFH - above the slab.

We are not discussing Under Floor Heating!

Otherwise below. Having the mass of the concrete above has benefits.

Even if it completely saturated and been subjected the weather, remember the swimming pool?

The same as having the insulation in the cavity as opposed to the inner surface if the walls.

Are we now discussing thermal mass?

 

[stuart45]

Both methods of construction can be used, although where I live now B and B is the normal because of ground conditions.
Main benefit of insulation below the slab is to do with the way the property is heated. The slab can be a heat store but the room does take longer to heat up.

 

[noseall]

Are we now discussing thermal mass?

Since you asked, yes.
Where do you get this whole swimming pool thing in any case?
The same thing can apply, membrane and VCL wise in both scenarios, as can the whole water ponding thing.
You can still lay another membrane prior to screeding in both scenarios.

 

[cAtLeYx]

Where do you get this whole swimming pool thing in any case?

You have excavated large hole in the ground to allow for your ground floor make up. Lets say we reduce levels based on the following conditions.
The home owner has a finished floor level of 0
To gauge the new extension floor to the existing, bearing in mind the make up advised by the OP was sand blinding say 20mm, insulation say 75mm and a concrete slab say 100mm (in my opinion should be more)
You now need to reduce the external ground levels by 20mm + 75mm + 100mm = 195, lets call it 200mm.
You now have an reduced level dig of 200mm (yes I know the exiting ground levels will play a part in this.
You excavate and cast you foundation, say a further reduction in ground levels of 700mm = foundations at 0 minus 900mm.
You construct your sub-structure blockwork up the DPC level, lets sat 150mm above the finish floor level of 0 = +150MM
This is where the problem comes, you lay a layer of sand (Blinding) to protect the VCL from any potential damage (Not a great idea) The VCL is lapped up the inside of the substructure blockwork to DPC level - This equated to an up-stand of VCL of approximately 350mm.
You install your nice dry insulation 75mm thick
You cast a concrete slab on top your nice dry insulation say 100mm thick (We haven't even discuss the water contamination form the concrete.
You now have a 350mm deep swimming with your 75mm insulation at the bottom and 100mm of concrete over it.
At this point the the works carried out to date are open to the elements. It pours down with rain as advised by the OP and there you have it -

A swimming pool.

The same thing can apply, membrane and VCL wise in both scenarios, as can the whole water ponding thing.

No - The concrete slab is cast on type one compacted stone. You could hose it down with a hosepipe all day long. Once the structure is completed and watertight the VCL in laid over the slab thus stoping any moisture from being on the nice dry warm side of the fabric. The wet slab below will happily sit their and dryout / keep getting wet without effecting the internal fabric.

You can still lay another membrane prior to screeding in both scenarios.

If you instal an additional VCL over the slab there is no possible way of the water escaping as its now trapped between the VCL below & the VCL above - You can't have two VCL - Its a one way street.

 

[noseall]

You forgot to add the other layer of DPM over the insulation prior to casting the slab. Oh, and you seem to be relying on it raining directly prior to the pour, to substantiate your argument.
Are you sure you are in the building trade? You seem either very new to it or a wee but naive.

 

[cAtLeYx]

Ok - so we add a separating layer into the mix - I have explained the construction detail that should be used. I have backed this up with my reasons for this and explained the senerio of what has been installed by the OP's builders and the detrimental effects of water ingress into this detail. Perhaps you could do the same for the alternative method that is being used by the OP builder.

 

[cAtLeYx]

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View attachment 87668

Oh, and you seem to be relying on it raining directly prior to the pour, to substantiate your argument.

The OP advised is was raining ?