Ubakus or Kingspan U-values right?

[Sparrowhawk]

This is doing my head in. I've done a suspended floor build up accurately in Ubakus and get a U-value of over 0.3W m^–2 K^–1 which seemed high; then did the same in Kingspan's calculator and got 0.19W m^–2 K^–1 .

 

Is there some obvious error I've made? Trying to work out if I can comply with Part L for upgrading existing floors...

 

 

 

[JohnMo]

6 minutes ago, Sparrowhawk said:

This is doing my head in. I've done a suspended floor build up accurately in Ubakus and get a U-value of over 0.3W m^–2 K^–1 which seemed high; then did the same in Kingspan's calculator and got 0.19W m^–2 K^–1 .

 

Is there some obvious error I've made?

 

Your joists are on different centres, one at 350 the other at 450mm, so they wouldn't be the same.

 

Neither seem very good.

[Sparrowhawk]

1 minute ago, JohnMo said:

Neither seem very good.

 

No they're not. I lifted some 1920s floor downstairs to see how much space is available, and I have a 100mm floor joist with 100mm-130mm void under it. Right now I'm trying to see if I can even meet ADL for existing floors (0.25m^–2 K^–1) if I put some insulation in, given the void is shallower than it's meant to be.

[Redbeard]

Is Ubakus German, or did I make that up?! If it is, I wonder if they do not use the IP/90-type Perimeter/Area convention, which gives a lower 'base case' U value than the old 'Uninsulated floors are 2' - IIRC then you'd expect a higher U value. But then I may be talking rubbish since, even if it's German, this appears to be the English version, so maybe it does use IP/90

[ADLIan]

Is Ubakus treating this as a suspended ground floor? Does not appear to be.

[dpmiller]

Kooltherm is Phenolic, not PIR?

[SteamyTea]

3 minutes ago, dpmiller said:

Kooltherm is Phenolic, not PIR

This is the problem with using initials/acronyms/abbreviations.

Even after being involved in the plastic industry since the 1970s, I still get confused as to what people are really talking about.

Phenol based plastics were usually referred to as PFs, polyurethanes as PUs, polystyrenes as PSs, polyethylene as PEs.  Then the processing method makes it even harder, so expanded is E, but extruded is X.

Then it all goes wrong with materials like PIR, I can just about accept the PI bit for polyisocyanurate, but why the R at the end.

[Sparrowhawk]

11 hours ago, Redbeard said:

Is Ubakus German, or did I make that up?! If it is, I wonder if they do not use the IP/90-type Perimeter/Area convention, which gives a lower 'base case' U value than the old 'Uninsulated floors are 2' - IIRC then you'd expect a higher U value. But then I may be talking rubbish since, even if it's German, this appears to be the English version, so maybe it does use IP/90

 

It is German, and I can't see what they're using for permiter/area, if anything. Kingspan by contrast required those two values before calculating the results.

 

11 hours ago, ADLIan said:

Is Ubakus treating this as a suspended ground floor? Does not appear to be.

 

They only have an option for "floor", not ground floor. I can choose the space at the bottom to have air or earth in it, but AFAICT restricting what's at the bottom to those two settings is the main change vs modelling as a "wall" or "roof".

[Sparrowhawk]

46 minutes ago, dpmiller said:

Kooltherm is Phenolic, not PIR?

It is, the options on the Kingspan calculator are very limited (only this material, only 450mm joist centres) so it's going to come out better than the other.

 

But - I was hoping to verify on 2 calculators that 100mm PIR plus flooring would at least get me to 0.25?

[SteamyTea]

I found this simplified method online

 

IP 3/90 formula U = 0.05 + 1.65(P/A) - 0.6(P/A)2

 

Where:

U = U-value of the uninsulated floor (W/m2K).

P = Length of the exposed perimeter (m).

A = Area of the floor (m2)

https://cms.esi.info/Media/documents/Warma_UvaluesUFH_ML.pdf

 

I am not sure if it is right, the final number, 2, could possibly be ²

Apart from that, it is easy enough.

 

It would be nice to know what the real formula is.

 

[SteamyTea]

20 minutes ago, Sparrowhawk said:

But - I was hoping to verify on 2 calculators that 100mm PIR plus flooring would at least get me to 0.25

I did a calculation on this a while back.

 

Convert the 3D shape into a 2D topological shape i.e. work out the area of the periphery and add it to the floor area.

Then just calculate as normal.

 

So say your floor is 8m by 10m and 0.1m thick.

A = 80 [m²]

PA = 3.6 [m²]

 

TA = A + PA = 83.6 m²

 

Multiply by U-Value.

 

PIR k-Value = 0.022 [W.m^-1.K^-1] 

R-Value = 0.1 [m] / 0.022 [W.m^-1.K^-1] 

U-Value = 1 / ( 0.1 [m] / 0.022 [W.m^-1.K^-1]) 

 

U-Value = 0.22 W.M^-2.K^-1 

 

Then add/subtract for joists area and properties.

Edited April 18 by SteamyTea

[Sparrowhawk]

5 minutes ago, SteamyTea said:

So say your floor is 8m by 10m and 0.1m thick.

A = 80 [m²]

PA = 3.2 [m²]

 

"P = Length of the exposed perimeter (m)."
 

Clarifying that the exposed perimiter isn't 36m (the length) but we involve the thickness too? I hadn't taken that into account before, which would explain some odd numbers I was getting 🤡

Edited April 18 by Sparrowhawk

[SteamyTea]

3 minutes ago, Sparrowhawk said:

Clarifying that the exposed perimiter isn't 36m

Yes, I have just realised I mistypes and was about to go and edit it.

 

Fixed now, it works out as a total floor area of 83.6m² because the periphery area is 3.6m². (10m + 10m + 8m + 8m) x 0.1m = 36m * 0.1m = 3.6m

 

Edited April 18 by SteamyTea

[ADLIan]

A = GF area. P = perimeter length as you look at the plan view. In above 36m (not 3.6m, no thickness involved). P/A for most houses is approx 0.4

[SteamyTea]

Just now, ADLIan said:

A = GF area. P = perimeter length as you look at the plan view. In above 36m (not 3.6m, no thickness involved)

I think we may be at cross purposes. 

I was not calculating the P/A ratio, just the thermal losses in a first order simplified manner.