Underfloor heating HELP!!

[GMajor13]

I am hoping you can help me with my underfloor heating problem.
I am currently building an extension to the rear of the property and have now decided after the floor has been prepped and signed off to try and install underfloor heating. Floor construction is MOT, sand blinding, DPM, 100mm insulation and a further layer of dpm. This leaves 100mm to reach DPC. Almost all recommendations by suppliers say that 100mm is too thick of a slab to place underfloor heating in and to reduce this to use a screed,however this means that the floor will not satisfy the required 100mm under regs. I lf I was to screed on top this would raise the floor in comparison to adjoining rooms. Help!

Has anyone any experience of laying UFH in a slab this thick and achieved decent results?
If so what effect does piercing the second layer of DPM have?
Any other suggestions on how I can still achieve UFH in my situation?
Many thanks in advance, I hope someone can help!!

 

[Chalker]

Why not use thicker insulation?

 

[GMajor13]

Why not use thicker insulation?

Does the concrete not have to be 100mm for regs?

 

[Dumbo]

I don't understand have you got insulation under the foundation slab ( oversight ) most floor build ups are slab , dpm , insulation , slip coat (thin guage membrane ) then screed . My screed at home is a pumped screed about 55mm thick most sand and cements are about 75mm .

 

[Andy Allen]

Do you mean piped ufh..?

 

[GMajor13]

I don't understand have you got insulation under the foundation slab ( oversight ) most floor build ups are slab , dpm , insulation , slip coat (thin guage membrane ) then screed . My screed at home is a pumped screed about 55mm thick most sand and cements are about 75mm .

The floor is prepped to pour the floor slab.
The build up is;
MOT
Sand blinding
DPM
100mm insulation
DPM
This now leaves 100mm (required concrete) to dpc to fill with concrete that I would like to fit wet piped UFH in.

 

[One Day]

50mm kingspan + ufh with 50mm anhydrite screed. Simple.

 

[Dumbo]

Sorry wasn't following mot as being scalpings . Just increase your insulation thickness

 

[GMajor13]

Sorry wasn't following mot as being scalpings . Just increase your insulation thickness

Thanks JCRtiling for your responses. Surely this won't work though as then I won't achieve the 100mm floor thickness BC require

 

[jobdone]

Is there not another layer of screed to go on the slab

 

[Chalker]

Looks like your missing the 100mm oversize concrete!
His is how it should be done.

 

[Kyle Knowles]

View attachment 92767 Looks like your missing the 100mm oversize concrete!
His is how it should be done.

That's exactly how I've done the last couple I've done #screeding is much harder that tiling

 

[Dumbo]

I just started typing when I saw new posts . So it should be . Mot . Sand . Concrete slab . Dpm . Insulation . Slip coat . Screed .
Concrete slab could be replaced by block and beam .

 

[GMajor13]

This is my current make up. Is there anything I can do at all? Thanks for all your help everyone

 

[hmtiling]

is the point here that the insulation can be over 100mm and 100mm is minimum requirement? therefore add more insulation as already stated?

 

[GMajor13]

is the point here that the insulation can be over 100mm and 100mm is minimum requirement? therefore add more insulation as already stated?

No the point is the concrete must be 100mm and the top of the dpc as you can see from the photo is 100mm from dpc.

 

[Dumbo]

Something is wrong here what your describing is not how a floor build up should be .

 

[GMajor13]

it can be achieved in either way in which case as no concrete has been poured could I change the build up. Could I screed the floor above dpc level with underfloor heating in?

 

[Ajax123]

Give me a call on Monday and I will go through it with you and draw you up a NBS spec. Imperial iS quite right 50mm insulation and 50mm screed is find for anhydrous. Concrete iS NOT a requurement if the. My number is 07966651006.

 

[Ajax123]

No the point is the concrete must be 100mm and the top of the dpc as you can see from the photo is 100mm from dpc.

This is one way to do it but not the only way.

 

[GMajor13]

I suppose the only issue may be I have already installed 100 insulation

 

[Dumbo]

View attachment 92782 it can be achieved in either way in which case as no concrete has been poured could I change the build up. Could I screed the floor above dpc level with underfloor heating in?

Yes I believe so

 

[Ajax123]

I suppose the only issue may be I have already installed 100 insulation

Why? You're allowed to put some more in if you want to....

Basically

Sand blinded well compacted hard core
1200gauge DOM
Insulation (depth and grade according to need)
Minimum 500gauge slip membrane
Underfloor heating
Minimum 50mm Gypsol XS screed

As I said. If you want a NBS spec for the architect and buildin control call me on Monday and I will sort it for you. Simpler. I will even sort out some installers for you to get prices from.

 

[Ajax123]

Domestic Extension Whaplode - http://gypsol.co.uk/case-studies/refurbishments/domestic-extension-whaplode