polystyrene u values, concrete floor

[mointainwalker]

Raize

I wrote :

100 mm of expanded polystyrene has a U value of 0.4

I did not write :

Polystyrene has a U value of 0.4

I'm not fussy, any kind of apology will do.

 

[Raize]

100mm of Polystyrene still doesn't have a U Value of 0.4.

Let me educate you just for a minute. Indulge me.

A singular item, be it 100mm Polystrene, or Celotex, or a airated block does not have a U Value. It is impossible.

A U Value is the result of a calculation including the thermal conductivities of every component in a construction.

EVERY item used in construction has a thermal conductivity. From the bricks, the roof tiles, to the nails and screws you use.


So yes, you are correct mointainwalker; I missed a word out when I quoted you.

You are still wrong though.

And don't worry, I don't want an apology.

 

[Norcon]

A singular item, be it 100mm Polystrene, or Celotex, or a airated block does not have a U Value. It is impossible.

So if I constructed a wall with 100mm of polystyrene, it doesn't have a U value?
Which in turn means it doesn't have any thermal transmittance and therefore no heat loss. Fantastic.

 

[Raize]

A singular item, be it 100mm Polystrene, or Celotex, or a airated block does not have a U Value. It is impossible.

So if I constructed a wall with 100mm of polystyrene, it doesn't have a U value?
Which in turn means it doesn't have any thermal transmittance and therefore no heat loss. Fantastic.

If you constructed a wall out of polystyrene, the U Value would be the last of your issues.

In that bizzarre circumstance, that the only material in the wall was the polystyrene, then a U Value could be calculated. But the polystyrene itself does not have a U Value.

Look, a U Value is just the result of a mathematical calculation. That's all it is.

 

[Norcon]

But the polystyrene itself does not have a U Value.

So no thermal transmittance then?

 

[Raize]

But the polystyrene itself does not have a U Value.

So no thermal transmittance then?

Yes, it has a thermal transmittance. That is the Thermal conductivity (0.038W/mk) as mentioned previously. Thermal conductivity / lambda value is not a U Value.

 

[Norcon]

Yes, it has a thermal transmittance

So it has a U value then.

 

[Raize]

Yes, it has a thermal transmittance

So it has a U value then.

No, thermal transmittance / lambda value / thermal conductivity is not a U Value.

 

[Norcon]

U = Thermal Transmittance

 

[Raize]

T: +44 (0)845 769 7452 < Springvale (a polystyrene manfuacturer) technical

Tel: 01544 388 601 < Kingspan

T: 0901 996 0100 < Celotex

Call any of the above and ask them what the U Value of their products is. Then post back here and let me know what they say.

 

[Norcon]

If its someone clever they'll say the U value of 100mm of polystyrene= approximately 0.35W.m ² based on CIBSE guidelines.
So I can go ahead and build my wall and calculate the overall heatloss.

 

[theoldun]

Yes, it has a thermal transmittance

So it has a U value then.

No, thermal transmittance / lambda value / thermal conductivity is not a U Value.

Raize, as a thick old bricklayer, we find this very interesting and informative.
To re-cap EPS has a lambda of 0.038W/mK which should give a Resistance of 2.63m2K/w which should give a U value of 0.38W/m2K.
Is that right Raize? Our apologies if we are wrong.
oldun

 

[Norcon]

Thats correct. Though you could probably add on some surface resistances which would lower it a little.
Get yourself cibse Guide A oldun. I have two copies sitting on my desk in front of me.

 

[freddiemercurystwin]

So what's the U Value of polystyrene?

I dance a mean lambada too.

 

[Raize]

So what's the U Value of polystyrene?