170mm to achieve FFL

[iMCaan]

Hi

 

So we're close to installing UFH in our self build.

We have 170mm to FFL, which doesn't quite add up.

100mm insulation

50mm liquid screed

3mm (to 5mm) floor tile adhesive

10mm floor tile thickness

Total 163mm

 

How do we gain the remaining 7mm? Perhaps this could be gained by applying more screed and/or floor tile adhesive?

 

Thanks

[JohnMo]

Sorry to say this the insulation depth is not very good, so your UFH will not be the cheapest to run. 7mm isn't much in building terms, just add more screed.

[TonyT]

150mm min I would say, 200 ideal

[LiamJones]

On a heat loss calculator (from this forum), for a ground floor area of about 100m2, the difference is about £50 a year between 100mm and 200mm of PIR. How does one factor in the additional losses from having UFH?

[JohnMo]

1 hour ago, LiamJones said:

How does one factor in the additional losses from having UFH?

 

Basically the dT for the floor moves from being internal room temp compared to ground temp, to water flow temp to ground temp.

 

You basically need double the insulation for UFH compared to radiators to have an equal downwards heat loss.

[nod]

As others have already said 100 mil isn’t much But you have what you have If you are laying ceramic tiles You will need at least the thickness of the tiles that your laying 12 mil is normal  

 

[Conor]

Just show 5h3 screed guys where 5hry need to bring the screed up to and they'll take it from there. They'll start setting out and compare the datums across the floor. You'll find each external door threshold will be a bit different. Your tiler can make up for a few mm difference at each door. You could go to 125mm insulation but think it might be a bit tight for screed as leaves no margin of error.

[JohnMo]

14 hours ago, JohnMo said:

 

Basically the dT for the floor moves from being internal room temp compared to ground temp, to water flow temp to ground temp.

 

You basically need double the insulation for UFH compared to radiators to have an equal downwards heat loss.

 

@LiamJones

Not easy to modify the spreadsheet to get the full picture.

 

As I am a little late amending this, I have had to do a new post.

 

Although the water flow temp is directly related to the heat loss of the floor, it only occurs where the pipes are, so you are better to use the average floor temperature. But that is affected by how well the floor is insulated and the rest of the house.

 

The floor will transfer heat at a rate of 7ΔtA = W into the house (as stated by @TerryE )  Δt is the difference in floor to room temperature. Or rearrange to Δt = W/(7xA)

 

So for my house at the heat demand is around 3kW and floor area is 192m2.

 

3000/(7x192) = 2.2, so my floor needs to 2.2 degs warmer than the room at design temperature.

 

Once calculated you could add this figure to the calculation in cell B51. But in well insulated house there is little advantage.

[TerryE]

BTW, I discussed how I got the 7ΔtA figure in one of my blog posts, A Little Aside On Radiance.   When there is only a relatively small delta, say less than 5°C,  there is little convection, so maybe 80% + of the heat is actually radiative, and there is standard physics law for this that includes an adjustment factor called the emissivity.  This is a fraction that will 0.9 or so for non-reflecting surfaces, so the 7 number is a good ballpark, but remember the Δt is measure for average floor surface temperature over the day relative to the room temperature.

 

Edited October 13, 2023 by TerryE

[iMCaan]

Thank you all.

 

In regards to 100mm insulation, I have what I have now. I've not had the best of the experience with the build from the design stage onwards. Two architects and both didn't advice me of having more than 100mm insulation. 

 

thank you.

 

[Kelvin]

They all seem to default to 100mm. It was only me researching it that I found out you should put in more. I planned  for 210mm  but we ended up at 185mm. My architect said anything above 150mm was a waste of money! 

[saveasteading]

8 minutes ago, Kelvin said:

architect said anything above 150mm was a waste of money! 

But we know better than that.

I tend to agree though that there are diminishing returns that the manufacturers don't mention, especially to a large floor where the outdoors is a long way away.

It's really worth paying attention to insulation at the perimeter.

[JohnMo]

20 minutes ago, saveasteading said:

But we know better than that.

 

This where as a client you need to inform yourself of building design and what you want from it from the aesthetics, but also the building energy performance.

 

For me the self build journey isn't about turning up at the architect door and a few weeks later having a design and then blindly getting someone to build it for you. It's more about working with the architect to get the design and performance you want (even if outside the architect comfort zone), if you need to say no this is how we will do it, then do it. We are the client and as long as conforms or is better than the regs all is good.

 

Our architect has basically copied our design and building the same for himself a few on the west coast of Scotland, he had only done building standards builds prior to me demanding lots of changes and upgrades.