# u-value ( k17)



## lamb (12 Dec 2009)

Hi all

I am trying to work out the u-value in W/m2k of the kingspan k17 ( 52mm- which includes the 12.5 of plasterboard) insulated board.

I have checked the kingspan website and it has just to much detail and does not give this type of rating or i just can't see it ...

and also can't get any of this type of detail off the sei website.

thanks in advance

L


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## sydthebeat (12 Dec 2009)

lamb said:


> Hi all
> 
> I am trying to work out the u-value in W/m2k of the kingspan k17 ( 52mm- which includes the 12.5 of plasterboard) insulated board.
> 
> ...



its pointless trying to work out the u value of 1 element of construction. A u value of an element of construction such as a wall, floor roof etc... is the inverse of teh sum of all teh resistances.

materials have 'thermal conductivity' (TC) values.

The thermal resistance of the material is the thickness divided by the TC value.

The thermal resistance (R) of a construction is the sum of all the thermal resistances.

The U value is the inverse of this total resistance.

you will find many thermal conductivities here, on page 36:
http://www.environ.ie/en/Publication...d,19069,en.pdf

calculating u values is not easy.... there are also conventions to be considered. they are contained here:
http://www.bre.co.uk/filelibrary/pdf...Edition%29.pdf


my advice.... engage a professional (preferably an architectural technician) to calculate your proposed u values.... 

u valuate here is a good tool: [broken link removed]


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## onq (12 Dec 2009)

+1 

Happy to let others crunch the numbers where appropriate.
Some of the drawings on the fasttrackcad site seem quite old.
Slight concern arising in terms of someone deciding to use them.

FWIW

ONQ.


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## galwaytt (14 Dec 2009)

sydthebeat said:


> its pointless trying to work out the u value of 1 element of construction.


 
...even so, you can't work out the sum total, without knowing the properties of the individual parts anyway, so he still needs to know it.

I agree, the Kingspan site is a minefield..........drives me mad.   I notice this is like a lot of the larger corporate ones - the bigger the corporation, the more  complex the site.  DuPont, DOW, etc all similar.......unfortunately....

Xtratherm's is more straightforward.


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## sydthebeat (14 Dec 2009)

galwaytt said:


> ...even so, you can't work out the sum total, without knowing the properties of the individual parts anyway, so he still needs to know it.



no he doesnt...

he needs to know the thermal conductivity of the material he is choosing... not the u value....

i should clarify....

knowing the u value of a piece of material has no constructive use. 
for example, using the OPs query.... "whats the u value of kingspan K17 board?"

kingspan K17 kooltherm board is a composite board made up of phenolic foam and gypsum plasterboard. 
The phenolic foam has a thermal conductivity of 0.022 W/mK.
The plasterboard has a TC value of 0.18.

If he/she uses a 52.5mm board it would have u value of 0.55 W/m2K
If he/she uses a 42.5mm board it would have u value of 0.73 W/m2K
If he/she uses a 62.5mm board it would have u value of 0.45 W/m2K

etc etc...

therefore the u value depends on the thickness and thermal conductivity.

If the op is looking to select between different products he / she should compare the thermal conductivity values as a measurement of which is "better" than others.


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## onq (14 Dec 2009)

sydthebeat said:


> <snip>
> If the op is looking to select between different products he / she should compare the thermal conductivity values as a measurement of which is "better" than others.



Da terminal conductor is yer only man.

Seriously though, the end result is to assess the construction as a whole and the sum of the parts are as important as each part.

Boundary layers between air and another material are important as is whether the cavity is vented and the insulation mechanically fixed.

FWIW

ONQ.


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