Liquid screed without concrete.

[ringi]

If I carefully dig up my exisiting floor in our 1930 bungalow, do I need concrete under the insulation if I have liquid screed over the UFH pipes?

 

If I was to put UFH pipes in concrete, how good a finish does self level concrete give?  Eg how much additional levelling before carpets/LVTs?

 

Practically how do I level under the insulation?

 

(The walls seem not to concrete foundations but to be at least a foot deeper then floor level.)

[Russell griffiths]

Self levelling concrete is not easy to find, lots of plants don’t do it, then if you do find it you will have minimal orders and increased costs, so you will probably end up with normal concrete. 
you will not get a good enough finish for any sort of LVT and nobody will lay LVT without doing there own preparation work. 
so allow for needing a smoothing / leveling compound on top of your concrete, this could be anything from 3-5-10mm thick, depending on how well the concrete was laid. 
 

or easier in my opinion to lay concrete first then insulation then ufh then liquid screed to cover the pipes. 
 

everyone has an opinion of how to do it. 

[Jilly]

Ask @SteamyTea, you need a lot more insulation than you think for ufh to be efficient. 

[saveasteading]

9 hours ago, ringi said:

dig up my exisiting floor

How deep?

Presumably this is a concrete floor, probably 4" thick.

So you would need to remove that and then hardcore, sufficiently for your new construction.

100mm concrete, at least 100mm insulation, 75mm screed.

That's a lot of work.

Liquid screed pours level but will have various lips that you can rub down.

 

[Iceverge]

You could do from the top

 

100mm concrete+fibers with UFH

Insulation 

Hardcore 

 

Put a DPM in there somewhere. 

 

Alternatively forget the UFH and put in large rads. And a thin layer of insulation on the current floor. 

 

[SteamyTea]

30 minutes ago, Jilly said:

Ask @SteamyTea, you need a lot more insulation than you think for ufh to be efficient. 

If you assume, that during the heating season, that the ground temperature is at 8°C, and your UFH flow temperature is at 32°C, then that is a difference of 24°C.

Now if we assume that the floor insulation has a k-value of 0.025 W.m^-1.K^-1 and the heating season is 120 days (2880 hours).

Then, for each m² of heating area you get:

 

 

So while there is diminishing returns on the insulation thickness, what has to be decided when digging, if the marginal costs.

Reducing the losses, will also reduce the heating season, but that does depend on the performance of the rest of the building as well.

 

 

[ringi]

2 hours ago, Jilly said:

Ask @SteamyTea, you need a lot more insulation than you think for ufh to be efficient. 

 

How much? I was thinking 100mm as minimalist with 200mm being more like it.  Hence careing about total thickness of concrete and screed.

 

[ringi]

2 hours ago, saveasteading said:

Presumably this is a concrete floor, probably 4" thick.

 

 

Given the dips in the middle of some rooms, I expecting more like 1".  So do we do a lot of levelling command and new radiators/pipework or UFH (done correctly)? 

[ringi]

If I do concrete, insulation, UFH.

 

How practical is it to get the concrete layed in one room as a time by a borrow mix company?

 

Do they level the concete well enough to install insulation directly on it?

 

I like the ideal of having a clean, mad free, site so I can personally install insulation/UFH so it is done correctly.  Also lets me decide the depth while digging done and seeing how deep the walls go.  Then decide if I can get enough insulation for UFH.

 

How does the cost of Liquid screed change if I do one room at a time?  Is mixing it myself rather then getting it pumped a sensible option?

[saveasteading]

26 minutes ago, ringi said:

How does the cost of Liquid screed change if I do one room at a time?  Is

Massively. Both on material and labour.

[ringi]

2 hours ago, saveasteading said:

Massively. Both on material and labour.

 

Thanks, is that also the case of doing two seperate 50 m^2 area then one 100 m^2 area?

 

The issue I getting is we have a dog and my wife is not good with stairs, so finding temporary accommodation is looking very hard.  (It does not help that both this government and the last government have reduced the number of people willing to be landlords.)