"Mary Fisher" wrote in message
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"Jim" wrote in message
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"Mary Fisher" wrote
In January 1993 we paid something over £300 for cavity wall insulation,

I am not familiar with this term. In the US, I have always used
paper-faced rolls of fiberglass stapeled between the wall studs. What is
CWI? The same? Sprayed foam/cellulose?
Thanks,
Jim


Houses built until fairly recently in Britain have only had an air gap
between the inner and outer walls of a house. That helped with insulation
and preventing damp. It was better than earlier buildings which were
single walled.

Newly built houses have built-in blocks (usually) of insulation between
the inner and outer walls.

Those of us with empty gaps can have them filled at our own cost or,
nowadays for many people, free. Because of not being able to access the
gap solid slabs can't be inserted so loose filling is blown into the gap.

In our case (and I think it's the most usual) holes are drilled in the
mortar between bricks at certain distances from each other, a pipe is
inserted and shredded mineral fibre is blown into the gap from outside.
It's a quick, if noisy, business, a lorry stands in the street with a
large bore hose leading to the house, the pump is in the back of the lorry
and can be heard from several houses away - that's how we know when
someone's having it done :-)

Afterwards the holes are re-filled with mortar and the workmen leave. As I
said, it's very quick and if you haven't had any wall insulation before
you can feel the difference immediately - far sooner than you can with
roof insulation although the fuel savings aren't as obvious.

I'm talking about brick-built houses of course, houses built from other
materials will probably have different means of providing insulation if it
wasn't built in from the start. I say that to avoid being flamed :-)

Mary

The filling is usually subject to a survey. As if there is damp on the
outer brick wall, the insulation in the cavity may take it to the inside
wall. The two walls were to prevent water ingress anyhow (well to overcome
poor quality workmanship in a building boom in the 1920s really). I think
the builders were giving guarantees with new homes and the cavity wall meant
that damp problems would be near eliminated. Cavity walls are unnecessary
in the UK, except in coastal windblown areas, yet they are standard. Some
cavity fill material makers say their materials do not allow moisture to
travel from the outer wall to the inner walls. You can't part fill, as
water may move across the top of the insulation material.

The only good thing about cavity walls is that they can be filled with
insulation to improve the thermal qualities of the house. If a wall is
designed for maximum insulation, it beats cavity walls hands down. It is an
expensive undertaking building two walls when one will do. The Germans
think we are mad.

I know of one block of apartments that had the cavities filled. The
residents complained that they were colder in the Spring. The solar gain
from the south facing walls never penetrated into the apartments. Overall
throughout the year they would have saved money on fuel and in winter the
places would be warmer.