On Wed, 10 Dec 2003 18:31:34 +0000, Andy Hall wrote:

On Wed, 10 Dec 2003 17:32:29 -0000, "Christian McArdle"
wrote:

When you add an extension, modern building regulations are going
to require cavity walls and double glazing and the heat losses
in this part are going to be a lot less (could be only a quarter)
of the equivalent size of existing house.

Indeed, I've heard of cases where adding a two storey extension has actually
resulted in reduced calculated heat losses from the house. This is because
an uninsulated solid wall was appended by the heavily insulated 2 storey
extension, which had considerably lower heat loss than the original wall,
despite have many times the surface area.

Christian.


The area doesn't need to be much for there to be an improvement.

The U value of a plastered solid double brick wall is about 2 W/m^2.K

For a new wall it's 0.35 or 0.25, so almost a 10:1 difference.

For old single glazed windows the improvement with double glazed, low
emissivity glass is about 2.5:1, although the areas are smaller of
course.

Not to mention the much reduced air changes which accounts for significant
part of the total heating demand.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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