Energy Performance Certificates and period buildings

[Nemesis]

I posted this in the HIPS sticky but thought it deserved a thread of its own:


http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2007/07/29/nhips129.xml

 

[ljn]

I agree this needs it's own thread. It's goig to be a big deal for all sellers of period buildings.

The fraze in the article:

"...our assessment is supposed to be a purely visual one. We are not obliged to be thorough."

Would suggest that they're not going to do a proper energy assesment, but wew are obliged to commission one and pay for it. But more serious is the stress of having to explain to a buyer that the survey I paid for is actually rubbish and misleading so please don't use it as an excuse for a discount.

 

[MdB]

This article really does make a nonsense of the whole energy rating scheme. I'm not planning on selling my house but I am keeping this in mind as I do work on it. One important improvement I will be making is adding lots of insulation (floors, walls, roof etc) so I guess I will need to record carefully everything that goes in so I can show an assessor when they come around.

Just out of interest, does anyone know how a rubble wall is rated? Is it just done on thickness or does the type of mortar / type of stone get taken into account? I can't imagine that thickness is an accurate measure but can't think of any other way it would be done.

 

[Penners]

Just out of interest, does anyone know how a rubble wall is rated?

On the "we're-not-obliged-to-be-thorough" principle, I reckon it's glanced at, then the inspector closes his eyes and sticks a pin in the energy rating chart.

:roll:

 

[MdB]

Just out of interest, does anyone know how a rubble wall is rated?

On the "we're-not-obliged-to-be-thorough" principle, I reckon it's glanced at, then the inspector closes his eyes and sticks a pin in the energy rating chart.

:roll:

Wouldn't surprise me at all. I do need a figure though so I can do some heat calcs on my house to work out what power heating system I need.

 

[Penners]

Sorry - you'd need to ask someone who knows what they're talking about.

i.e. not me!

 

[Gervase]

There is no hard and fast formula for rubble stone. As one English Heritage chap put it to me: " A 900mm thick rubble wall will have very good insulation value provided it is solid. However, all old walls have voids and it is by no means certain what material is inside the core. Calculating a U value can be meaningless."
However reference to the Chartered Institute of Building Services Engineers' Guide A includes the thermal performance and U values for most materials which are available, for example the thermal conductivity of lime plaster (thickness not specified!) is given as 0.8 w/mk while the U value for stone walls 6oomm thick with 50mm air gap with 25mm dense plaster on laths is 1.38 w/m2.
So they say! But, as mentioned, such figures are pretty meaningless.

 

[biffvernon]

for example the thermal conductivity of lime plaster (thickness not specified!) is given as 0.8 w/mk

'scuse me, but one wouldn't specify the thickness for the thermal conductivity as that's what the 'm' in the units is for.

I'd guess that small voids within the rubble would increase insulation while big voids that allow convection would reduce insulation. Doubtless an x-ray examination will be part of the HIP.

 

[Gervase]

 

[MdB]

Original post deleted as I got it wrong (hopefully before too many people read it...)

Thermal conductivity (W/m.K) is not the same as U value (W/m^2.k) though they are related as follows:

U Value = Thermal conductivity / thickness (ignoring convection and radiation)

so lime plaster with a Thermal conductivity of 0.8 W/m.K would have a U value of 32 W/m^2.K if it was 25mm thick.

I think I have got that right now.

 

[Penners]

The only words I understood in the last three posts were "void" and "thick".

Says it all, really.

 

[Nemesis]

Don't worry Penners - you are not alone!

 

[ljn]

English Heritage's view:

http://www.english-heritage.org.uk/upload/pdf/Advice-DEA.pdf


Liam