On Sun, 10 Aug 2003 22:36:37 +0100, "IMM" wrote:




If you do the heat loss (or gain) calculations for a brick and block
property with tiled roof, having ridiculous amounts of space wasting
insulation in the roof space is making no more than a tiny difference
when set in the context of what is gained or lost through the walls
and windows.

Figures and evidence please. Not rambling thoughts.

I already did this once for you and
not very long ago. Would you
like me to dig out the figures that
demonstrate once again that you
are talking nonsense?

You claim anything over 100mm of loft insulation is not worth it. Please
convince me. Don't make it up.

It's pretty simple.

Consider a detached property with an overall footprint of 8m x 8m and
a height of 5m to the eaves. Floor is concrete throughout and there
is a pitched, felted roof. Walls are brick and block with 50mm
cavity insulation. All rooms are at the same temperature of 21
degrees, and the outside is -3 degrees. There are a total of 10
rooms with an average window size of 1.5 sqm in each, and patio doors
3m x 2m

Using the required U values from the Approved Documents to the
Building Regulations:

Floor U = 0.25
Walls U = 0.35
Windows U = 2.0
Roof U = 0.16



Floor area = 64m^2
dT = 24
Heat loss = 64 x 24 x 0.25 = 384W

Window area = 21m^2
dT=24
Heat loss = 21 x 24 x 2 = 1008W

Wall Area = 8m x 5m x 4 = 160m^2
less 21m^2 windows
net wall area = 139m^2
dt = 24
Heat loss = 139 x 24 x 0.35 = 1168W

Roof area = 64m^2
dt = 24
Heat loss = 64 x 24 x 0.16 = 246W


This comes to a total of just over 2800W
In addition, in order to heat the average number of air changes of
1.5 per hour, additional heat of 3975W is required making a total of
6775W.

If the U value of the roof were increased to 0.36, which is the approx
value if 100mm of insulation were used, the heat loss through the roof
increases to 554W, the difference being 308W.

In other words, the saving is 308/6775 = 4.5%

In comparison to the walls and windows it's negligible.


If you were to take a slightly older property having twice the U
values for each surface, the improvement gained by going for more than
100mm of insulation drops to between 2 and 3 %.


Strange that current building rags are over 100mm

That depends on the type of insulation, of course. Frankly it's
demonstrably window dressing to play the Kyoto game.

and in 2007/8 they will be
well over.

You've seen the Statutory Instrument?

Maybe you know something the BRE, the Germans, Dutch,
Scandinavians and North Americans don't know.


Not really, but the figures speak for themselves.

It's window dressing.


..andy

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