Hi.

I need a basic chart showing the heat losses through a loft area if
there is no insulation, 50mm, 100mm up to the 265mm nominal 'perfect'
insulation. Anyone know where there is one or the facts (validated)
so I can draw one up for myself?

Along the lines of...

One sq metre of uninsulated plasterboard has a U value of... ?
Ditto with 50 mm standard rolled fibre insulation.
Ditto with 100 mm, 150 mm etc.

It's so I can show someone a comparison so she can decide just when
enough is enough compared with keeping spending more and more on more
materiels.

I am googling, and it's ongoing, but all I find so far is detailed
tech guides or company ads. I'll bet someone on here has a link
already!

Thanks.

Mike Barnard wrote:
Hi.

I need a basic chart showing the heat losses through a loft area if
there is no insulation, 50mm, 100mm up to the 265mm nominal 'perfect'
insulation. Anyone know where there is one or the facts (validated)
so I can draw one up for myself?

Along the lines of...

One sq metre of uninsulated plasterboard has a U value of... ?

K value for plasterboard is 0.16. So U value of 16 for 10mm thick.. or
16 watts per square meter per degree centigrade.


Ditto with 50 mm standard rolled fibre insulation.

k value of glass fibre around 0.034 so a U value for 50mm is 20 times
that. 0.6 pr so? seems wrong..no..thats more or less right.

Ditto with 100 mm, 150 mm etc.


Divide by 2, 3 etc..


It's so I can show someone a comparison so she can decide just when
enough is enough compared with keeping spending more and more on more
materiels.


Note that when loose fiber insulation is used, the value of a WINDPROOF
layer like plasterboard is really high. Its not the same with celotex,
which is windproof to start with.

In terms of loft insulation around 100mm of rockwool, windproofed to the
hilt, is probably the best cost-benefit compromise.

If you want a useable surface there , fill between joists totally with
rockwool, then screw some 2x4s across the lot and fill again, then plate
over with chipboard.

If its to be left unused, then lay that last layer across the joists
instead.



I am googling, and it's ongoing, but all I find so far is detailed
tech guides or company ads. I'll bet someone on here has a link
already!

Thanks.

The Natural Philosopher wrote:

K value for plasterboard is 0.16. So U value of 16 for 10mm thick.. or
16 watts per square meter per degree centigrade.

Nonsense - you've forgotten to include the surface boundary layer
resistances.

For calculation principles and up-to-date data see BRE publication 443:
http://www.bre.co.uk/filelibrary/BR_...6_Edition).pdf

--
Andy

Andy Wade wrote:
The Natural Philosopher wrote:

K value for plasterboard is 0.16. So U value of 16 for 10mm thick.. or
16 watts per square meter per degree centigrade.

Nonsense - you've forgotten to include the surface boundary layer
resistances.

Who said I should?

That was straight out of te building regulations hand book.

Take it up with them.

I tend to trust them more than you.




For calculation principles and up-to-date data see BRE publication 443:
http://www.bre.co.uk/filelibrary/BR_...6_Edition).pdf

On Sun, 30 Dec 2007 01:04:01 +0000, a particular chimpanzee, The
Natural Philosopher randomly hit the keyboard and produced:

Andy Wade wrote:

Nonsense - you've forgotten to include the surface boundary layer
resistances.

That was straight out of te building regulations hand book.

I tend to trust them more than you.

But he is right. The Resistance value of all the elements is added
together to give the total R-value; a U-value is the reciprocal of
this. The R-value includes the surface resistances of the inside and
outside surfaces (IIRC, between 0.35m²K/W to 0.04m²K/W depending on a
few factors).
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

Hugo Nebula wrote:
On Sun, 30 Dec 2007 01:04:01 +0000, a particular chimpanzee, The
Natural Philosopher randomly hit the keyboard and produced:

Andy Wade wrote:

Nonsense - you've forgotten to include the surface boundary layer
resistances.

That was straight out of te building regulations hand book.

I tend to trust them more than you.

But he is right. The Resistance value of all the elements is added
together to give the total R-value; a U-value is the reciprocal of
this. The R-value includes the surface resistances of the inside and
outside surfaces (IIRC, between 0.35m�K/W to 0.04m�K/W depending on a
few factors).

Highly dangerous factors. A ripping wind in the loft makes mockery of
them for a start. And reduces rockwool insulation hugely.


However the OP did not ask for the total resistance of this or that
construction, Merely the U values of the materials. That stands as written.

If you want the total U value of a construction do the maths and add in
the boundaries.

BUT as I said, its dangerous to rely on them.

Anyone who has blown on his hands to warm or cool them can tell you that.

Judging by my boiler on times, `I lose 2-4 times more heat in a 20mph
wind...

The difference when I fully boarded out 150mm rockwool in the loft was
immense.

A fan blown heatsink will do about 5-20 times more heatloss than a
convection cooled one. OH its DESIGNED to do that, which houses are not,
but the U value calculations are VERY optimistic if they rely on ANY
boundary layer outside the house, or in a 'cold' loft' whatsoever.

On Sat, 29 Dec 2007 13:51:04 +0000, Mike Barnard
wrote:

Hi.

I need a basic chart showing the heat losses through a loft area if
there is no insulation, 50mm, 100mm up to the 265mm nominal 'perfect'
insulation. Anyone know where there is one or the facts (validated)
so I can draw one up for myself?

Along the lines of...

One sq metre of uninsulated plasterboard has a U value of... ?
Ditto with 50 mm standard rolled fibre insulation.
Ditto with 100 mm, 150 mm etc.

It's so I can show someone a comparison so she can decide just when
enough is enough compared with keeping spending more and more on more
materiels.

I am googling, and it's ongoing, but all I find so far is detailed
tech guides or company ads. I'll bet someone on here has a link
already!

Thanks.

Interesting answers, thanks. All I really need to know is whether
adding another 150mm of insulation will make a big difference to the
existing 125mm. So If I had a chart as described I'd have an idea of
a 'typical' heatloss for various depths. At what point does it become
pointless (oops, bad english) to add more? Is it worth 300mm? 500MM?
Where does one reasonably stop?

On Sat, 29 Dec 2007 13:51:04 +0000, a particular chimpanzee, Mike
Barnard randomly hit the keyboard
and produced:

I need a basic chart showing the heat losses through a loft area if
there is no insulation, 50mm, 100mm up to the 265mm nominal 'perfect'
insulation. Anyone know where there is one or the facts (validated)
so I can draw one up for myself?

I am googling, and it's ongoing, but all I find so far is detailed
tech guides or company ads. I'll bet someone on here has a link
already!

The 2002 Approved Document L1 (Dwellings) is still available on the
Planning Portal
(http://www.planningportal.gov.uk/upl...ADL1_2002.pdf).
This had some useful and not-so-useful tables in the back.

What you will hopefully see is that it's not a simple straight-line
graph where doubling the insulation halves the heat loss. It isn't.
It also depends on the proportion of heat loss through bridging
elements such as ceiling joists. It is also subject to diminishing
returns, where a small initial amount of insulation has seemingly
dramatic effects but subsequent thicknesses have less and less effect.
This is where other factors affecting heat loss and energy use such as
airtightness come in.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

Mike Barnard wrote:
On Sat, 29 Dec 2007 13:51:04 +0000, Mike Barnard
wrote:

Hi.

I need a basic chart showing the heat losses through a loft area if
there is no insulation, 50mm, 100mm up to the 265mm nominal 'perfect'
insulation. Anyone know where there is one or the facts (validated)
so I can draw one up for myself?

Along the lines of...

One sq metre of uninsulated plasterboard has a U value of... ?
Ditto with 50 mm standard rolled fibre insulation.
Ditto with 100 mm, 150 mm etc.

It's so I can show someone a comparison so she can decide just when
enough is enough compared with keeping spending more and more on more
materiels.

I am googling, and it's ongoing, but all I find so far is detailed
tech guides or company ads. I'll bet someone on here has a link
already!

Thanks.

Interesting answers, thanks. All I really need to know is whether
adding another 150mm of insulation will make a big difference to the
existing 125mm. So If I had a chart as described I'd have an idea of
a 'typical' heatloss for various depths. At what point does it become
pointless (oops, bad english) to add more? Is it worth 300mm? 500MM?
Where does one reasonably stop?


Where the loses from other sources exceed the losses from the bits you
are insulating.

In a house to modern standards, it is in fact the trickle ventilation
that sets an upper limit on how much its worth insulating.

That and unavoidable 'cold bridges' around window and door frames.