Underfloor heating pipes within concrete slab

[Smallholdertoo]

We are finalising the plans of a one and a half storey house (c.90m2 footprint). This will be well insulated -with u-values of walls .12, roof .10 and the insulated structural raft 0.10. It will have MVHR, so should have a heat requirement of around 2kw even when -10celcius outside.

 

I suggested to the SE that UFH pipe would be within the power floated structural raft and this was his response 

• "I am apprehensive about this detail as there are several risks including damage to the system during pouring of the raft and the requirement to maintain sufficient cover to the reinforcement. I suggest that the more conventional screed-based systems may be more suitable and would likely make the detailing of wet rooms etc. easier."

 

I would still like to go this route. I am not convinced that there be any material increase in risk from having the pipe in pumped concrete as compare with a pumped liquid screed.  Any damage is more likely to come from hobnail boots than the concrete. and in regards to his comment re coverage, this could easily be addressed by increasing the depth of the slab by 25mm. This cost of 2m3 extra concrete is tiny compared with the hassle and cost of 60mm of screed.

 

I accept his point re the wet room. I am unsure how to address this other than having shuttering to reduce the height of the concrete where the wet room is and screed to hive required levels. 

 

Any thoughts how should I respond.

[JohnMo]

3 minutes ago, Smallholdertoo said:

hobnail boots

Think it's more likely the ground workers will be wearing wellies during the pour.

 

How thick is your raft concrete?

8 minutes ago, Smallholdertoo said:

accept his point re the wet room. I am unsure how to address this other than having shuttering to reduce the height of the concrete where the wet room is and screed to hive required levels. 

Confused by the comment on wet rooms?

 

[Mr Punter]

I have seen a few situations where UFH pipes float in concrete and can be damaged by power floating / polishing, so be a bit wary.

 

The slab will take a long time to heat and cool as I am sure you are aware.

[Smallholdertoo]

1 hour ago, JohnMo said:

Think it's more likely the ground workers will be wearing wellies during the pour.

 

How thick is your raft concrete?

Confused by the comment on wet rooms?

 

Agreed wellies are unlikely to damage the pipe.

 

Thickness not yet finalised SE has yet to do soil analysis  but 250mm has been mentioned.

 

Wet room issue relates to how to plan for appropriate falls in the downstairs wet room to ensure that water runs to the drain..  Screeding feels like it may be better for adjusting levels in a  small area.  If I'm honest I haven't a clue  how to address the drainage of the wet room. 

 

Suggestions welcome!

[Conor]

Loads on here have done this with no issues.

 

For shower areas, just shutter off the area.

 

Do you need to have a drain in the middle of a room and then have a fall to it?! We've two bathrooms with walk in showers and didn't do anything like that. 

[Smallholdertoo]

24 minutes ago, Mr Punter said:

I have seen a few situations where UFH pipes float in concrete and can be damaged by power floating / polishing, so be a bit wary.

 

The slab will take a long time to heat and cool as I am sure you are aware.

I guess the intention will be to tie the pipe to the rebar that will be 200mm apart.  Would it help if the manifold was pressurised with water?

 

I accept it will be slow to change temperature . Thanks for your comments.

[Smallholdertoo]

2 minutes ago, Conor said:

Loads on here have done this with no issues.

 

For shower areas, just shutter off the area.

 

Do you need to have a drain in the middle of a room and then have a fall to it?! We've two bathrooms with walk in showers and didn't do anything like that. 

As this is something I have never done, does shuttering off the area work for a reinforced raft?

 

The drain will be at an edge rather than the middle.  How did you do yours?

[Conor]

Just now, Smallholdertoo said:

As this is something I have never done, does shuttering off the area work for a reinforced raft?

 

The drain will be at an edge rather than the middle.  How did you do yours?

Yes. Just timber and ply box a bit bigger than your intended shower tray. Need to carefully plan these things now.

 

Will the floated concrete floor be your finished floor? If not, it's a simple matter of bringing the sewer pipe up to where the water trap will be and shuttering off a big enough area to fit the trap. A fall, if needed, can be done via tiling.

 

Unless of course the concrete will be your finished floor, in which case all of the above is a complete pain.

[Smallholdertoo]

25 minutes ago, Conor said:

Yes. Just timber and ply box a bit bigger than your intended shower tray. Need to carefully plan these things now.

 

Will the floated concrete floor be your finished floor? If not, it's a simple matter of bringing the sewer pipe up to where the water trap will be and shuttering off a big enough area to fit the trap. A fall, if needed, can be done via tiling.

 

Unless of course the concrete will be your finished floor, in which case all of the above is a complete pain.

Many thanks for your responses - Luckily the concrete will not be the finished floor. We will be tiling over it!  

 

Are you aware of any youtube videos that show this?

 

Edited October 22 by Smallholdertoo
add thanks

[JohnMo]

54 minutes ago, Smallholdertoo said:

250mm has been mentioned

So at that thickness you will have most likely two layers of rebar. They are usually 50mm of more below the surface. So zip tie at 200mm centres to rebar. Nothing will float up.  You have two opinions with UFH pipes fill with air or water glycol, water glycol less likely to float.

 

Plenty of examples on the UFH section on here.

[Tom]

We put half our UFH in the concrete slab and tbh this was far less of a pain to do than the other half we decided to lay on top of the slab and screed over.

Our slab was 200mm and had two layers of rebar mesh (actually four, two at the bottom of the slab and two at the top), I tied the UFH pipes to the bottom layers of mesh then put the top rebar layers on, separated by rebar deckchairs. I did this all myself so could make absolutely sure no pipes were damaged. Seems to have worked well.