Thermal ratings for building regs and what is best to use.

hwalkerh

Hi

We have a single brick extension that we are turning into a room. I believe to meet building reg we require a U rating for the walls of 0.35.

Although this is the requirement it seems to be the lowest that they do for thermal plasterboard and they do ones that go up to 1.05 of more.

Can you tell me what is the sort of rating i should be going for for a nice warm room and not just to meet building regs.

Thanks
Helen

vaio

U value is how many watts escape per square metre of wall for a standard fixed temperature difference between inside and outside.

So, the small the U value the better

Doozergirl

What vaio said; it's the smaller number the better. 0.35 is a very good U value, 1.05 is worse!

House_Hunter

I think the OP is really after examples of what U-value people have achieved and then qualitive statements about whether it was "warm and cosy" or not as opposed to an explanation of U-values...

Sorry OP...don't know much about U-values in modern buildings - we have solid walls that are freezing to touch!!

27col

hwalkerh wrote: »

H

Can you tell me what is the sort of rating i should be going for for a nice warm room and not just to meet building regs.

Thanks
Helen

Go for the lowest U no. that you can get. If thermal plasterboard is 1.05 then that will be three times worse than the required .35. In fact it would not even begin to meet the official requirement

hwalkerh

Many thanks for your responses. I think i may have been confusing things.

The thicker plaster boards come with large ratings but they call them Thermal resistant U values so I am guessing in the case of Thermal resistance the large the value the better.

Does anyone know if the Building reg 0.35 U value is the same as buying plasterboard with the 0.35 Thermal resistant U value?

Also what sort of thermal resistant U value plasterboard to people recommend to make a cosy and warm room?

Any help would be great.
Thanks

hwalkerh

http://www.british-gypsum.com/products/plasterboard___accessories/gyproc_thermal/gyproc_thermaline_basic.aspx

Here is a link for what i mean about the plaster board

The_Pedant

I think the Thermal Resistance figure is the 'R-Value'

U Value = how well a material conducts heat, so higher = more conduction, so worse insulation.
R Value = the thermal resistance and hence how well a material keeps heat in, so higher = more resistance, hence better insulation.

these two values are the reciprocal of each other, so divide 1 by the value you have to get the opposite value.

So, from that link:-
22mm board: R-value of 0.35 = U-value of 2.86
40mm board: R-value of 0.80 = U-value of 1.25

Remember to include your wall in any calculations, plus the cavity etc.

Can anyone confirm if I'm right in thinking that you just add up the r-values for each element in your wall and then convert that into the U-value? (Has been a while since I last had to work all this out).

If that is the case then you need to reach a total R-Value of about 2.86 to reach the required U-Value you originally mentioned.... I think :huh:

Petrarch74

Hi, From what i know, Pendant is correct, add up the U values and reciprocal is the U-value.

I also spoke to our thermal expert here and he says:

"I Would never recommend using an insulated dry ling board directly fixed to a single skin wall.
( Reason being, is that dampness from driving rain will penetrate the single brick and cause damage to the liner board)

Providing that the wall is relatively free of dampness, I would recommend fitting an independent free standing timber frame wall (not fixed directly to the brick wall) leaving a minimum 25mm cavity between the back of the frame and the wall.
Fill between the studs with 70mm Rockwool Flexi and then screw fix a 50mm Thermaline insulated plasterboard to the inner stud face. U Value =0.32 (calculated value)

You will need to inform L A building control of “ the change of use “ to habitable space otherwise it could jeopardise the sale of the property if this is apllicable."

Hope that this helps.