Hello, just trying to get my head round wet UFH in our conversion: The concrete is rough and unlevel in places so I'm hoping the screed will even things out, there is approx  200mm available in some places, but it varies. 

 

I'm planning:

 

10mm slate floor

65-70mm screed

100mm PIR 

The electrician has put the ring main on the floor so need to tuck the DPM under it. Is this ok touching the PIR? I read EPS can degrade plastic??

DPM

?? 10mm sand blinding?? or EPS?? Which sand is best?

original rough concrete slab with a slight slope

 

Which diameter of UFH pipes and which spacing is best to be the most flexible? Going to start with a Willis heater and save up for  ASHP, but might need a boiler .

Thank you!

2 hours ago, Jilly said:

100mm PIR

Not really enough in normal circumstances.

2 hours ago, Jilly said:

read EPS can degrade plastic??

Yes it does, your electrician will know all the regs about it, I hope.

I'll try and squeeze a bit more PIR in. 

 

So PIR is ok with the wires? (I'd intended to change after reading that Celotex degrades or something, so now I'm back to PIR!). 

 

Is it ok for the wires to go through the screed? He has used trunking, but only on the straight runs. 

 

Thank you. 

If you assume that a normal wall needs to cope with low losses when it is 20⁰C inside and 0⁰C outside, then you can work out an acceptable loss for a floor slab that may be 35 to 40⁰C but the ground will probably be no colder than 10⁰C. So 50% greater losses, and no solar gain available except what shines through windows in the summer, which is of no use.

 

Can you not put in conduit for all the buried cables, costs very little and gives you flexibility in the future i.e running cable for a car charger, shed, ASHP.

On 19/07/2021 at 18:03, SteamyTea said:

   On 19/07/2021 at 15:15,  Jilly said: 

100mm PIR

Not really enough in normal circumstances.

I'm using 100mm Kingspan Kooltherm K103 which gives a calculated U value of 0.15 w/m2 K 

 

Is this 'enough' for UFH in your opinion, Oh Esteemy One? ?

25 minutes ago, Jilly said:

using 100mm Kingspan Kooltherm K103 which gives a calculated U value of 0.15 w/m2 K 

Not really, in my opinion.

It is not the intrinsic properties of the materials used, it it the floor losses, as a percentage of your house losses. This is caused by the greater temperature differences that the floor is heated to, compared to an unheated floor.

So as an example, if your house needs 10 W/m² at a temperature differences of 10⁰C, you may find that 3 of those watts are going through the floor when it is at 18⁰C. But 7 are going through if you raise the temperature of the floor to 30⁰C.

It is just a case of doing the numbers and seeing how they compare.

 

0.15 W/m².K will be 3 W when the slab is around 28⁰C.

3 W does not sound much, but that is for every m², and all the time the heating is on, plus a bit when it is cooling down.

So if your slab is 100m², and the heating time is 1000 hours, that is 300 kWh.

Edited November 25, 20214 yr by SteamyTea

Ok...? I can't get any more in as it's a retro fit.

 

I suppose I just have to go with it because the screed is going in soon and there isn't much choice but to see how it performs in real life as I don't want forgo the option and then wish I'd done it.

 

So you are saying I'd be better with giant radiators which I don't have room for? 

What type of screed are you using? Can you reduce that to 50mm liquid screed and get up to 120mm insulation? That 20mm will help a lot. 

Alternatively are windows and doors fitted? Have you a stairs and what height is the ceiling? Any potential to raise the floor level by 20-30mm for example?

24 minutes ago, Jilly said:

So you are saying I'd be better with giant radiators which I don't have room for? 

No.

Saying you need to calculate the floor losses as a fraction of all losses.

You could fit a combination of traditional double radiators and skirting radiators, and possibly plinth, fan assisted ones.

Yes, the windows and doors are fitted.The floor is very uneven, so the screed will vary from 70mm to 40mm in places. The builder says the weight of the screed (unknown sort, sand and cement to be ordered with fibres thrown in) will sort out the unevenness. Sand blinding didn't do a great job. Its rocking where the bath is to go so need to think of something there. 

Edited November 25, 20214 yr by Jilly

@JillyFind out from someone who knows, (not me) about the minimum thickness for sand/cement screed with UFH pipework.

 

https://web.archive.org/web/20161103034245/http://screed.it/sandandcement.html