HOW THICK DOES NEW CONCRETE FLLOR NEED TO BE?

[dazza1304]

Hi there,

Was hoping someone could help me.

I live in an old property that I am refurbing. The ground floor currently has quarry tiled floors.

I want to lift the quarry tiled floor and put in solid floor with wet underfloor heating.

My question is haw deep do I need to excavate?

I am concerned if I dig too far I will undermine the footings. I have dug some test holes and can easily get 12 inches no problem - is this sufficient?

What I was thinking is 6" concrete then DPM, 3" celotex, underfloor heating, then 3" screed.

Is this OK, or do I need another 6" of compacted hardcore under the concrete (seems excessive to me!).

All advice appreciated.

 

[jeds]

Ideally you need 150mm of compacted hardcore. 100mm will do if ground conditions are favourable and well compacted beneath your existing - which is likely if it's been down a long time. Then blind the top of the hardcore with a layer of sand to protect the membrane. 150mm concrete is too much - 100mm is sufficient. The screed needs to be 65mm if the u/f pipes are within the screed.

So; 100 hardcore, 25-50mm sand, membrane, 100 concrete, 70 Celotex, u/f pipes, 65mm screed = about 380mm - or 15" in old money.

If the ground is really good a lot of people might just blind and concrete without the hardcore. But that depends what you find?

 

[dazza1304]

Thanks for the quick response.

Another question now!!

I am putting in 2 new bathrooms and was wondering, do I need to dig the soil pipe in below the hardcore or lay it in the hardcore?

 

[noseall]

Thanks for the quick response.

Another question now!!

I am putting in 2 new bathrooms and was wondering, do I need to dig the soil pipe in below the hardcore or lay it in the hardcore?

the height of the pipe will be determined by the depth of the existing drain onto which you wish to connect to and the relevant falls their-in.

the pipe will need to rise approximately 25mm every metre from the connection to existing.

 

[dazza1304]

Hi yes, I realise that, sorry should have stated that we are putting in a new connection to sewer so fall isnt a problem.

Just really wanted to know if soil pipes should come up vertically through, hardcore,blinding dpm etc, or if it can run horizontally through so to speak!


thanks...

 

[dazza1304]

Ideally you need 150mm of compacted hardcore. 100mm will do if ground conditions are favourable and well compacted beneath your existing - which is likely if it's been down a long time. Then blind the top of the hardcore with a layer of sand to protect the membrane. 150mm concrete is too much - 100mm is sufficient. The screed needs to be 65mm if the u/f pipes are within the screed.

So; 100 hardcore, 25-50mm sand, membrane, 100 concrete, 70 Celotex, u/f pipes, 65mm screed = about 380mm - or 15" in old money.

If the ground is really good a lot of people might just blind and concrete without the hardcore. But that depends what you find?

Hi there, ground has been undisturbed and compacted for about 150 years so is pretty firm!!

Does that mean I can do away eith the hardcore?

 

[noseall]

Just really wanted to know if soil pipes should come up vertically through, hardcore,blinding dpm etc, .

yup.

 

[mikric]

This work is also notifiyable to LABC

 

[marsaday]

i put ufh in my kitchen last yr and didnt need to notify BC. i got him out about the footings issue and he was happy. i dug out enough for 10cm concrete 7cm insulation and 4cm for blinding. so 20-22cm was dug out i think. no problems so far and tiles are down and heating works fine. was a wet system