"Terry" wrote in message
. ..

Another problem that can arise with very high levels of insulation and a
well sealed house, is large amounts of condensation.
In Scandinavian new builds I've seen this has been specially catered
for.


Well, sort of. But ..............
Here in Canada with longer colder winters (and often heat leaching winds!)
higher values of the insulation reduce heat loss and therefore the cost of
heating ones home. Since the energy cost increases of the 1970/80s etc.
much
thicker insulation has been the 'standard'. Most wood frame houses now
have
6 inch wooden stud outer walls filled with insulation and/or sheeted with
foam boards, older homes 4 inch.
But it is the 'vapour barrier' on the warm side of the insulation,
whatever
type and thickness it is, that is important. It prevents the warm air from
seeping out into the outer walls and ceilings. Warm air is moist; when it
cools down the moisture in it condenses into water and can cause rot,
mould,
damp/wet insulation and even condensation and water droplets in the attic.

It also makes the house air-tight reducing much heat loss in winter, and
gain in the summer. The Canadians have the R2000 standard, which is one the
most advanced in the world, if not the most. The Canadians, say "build
tight, ventilate right".

The Canadians don't just slap up the VCB, as they do here. It is
meticulously installed and properly taped up. The Canadians are
implementing the R2000 standard in the UK and Japan. Canadian companies
harve be involved with Uk companies, as the Uk companies just don't have the
skills levels, or can concenrrate long enough to carry out detailed work.

(Saw one roof where every nail in the loft/attic was rusty!) same thing,
on
a smaller scale, as occasionally happens in large stadia.during a
temperature change. i.e. "It rains indoors".
From time to time our National Government has provided incentives to
increase insulation values, typically and easily by adding several
additional inches to ceilings. Often easy to do using 'blown in'
insulation.
But emphasis is always on proper installation, adding to and not blocking
off attic air circulation vents and stressing the use of proper vapour
barriers and or/sealing leakage up into the roof space.
An improper or missing vapour barrier in the ceilings and no attic
ventilation can spell expensive major problems. See damp attics and
peeling
painted trim! One guy had 'mushrooms' (fungus) growing up there!
Most new Canadian houses now to qualify for mortgage, are built to R2000
specification; this does require a 'sealed' vapour barrier house with
extensive use of sealants around all interior wall apertures. That type of
construction therefore requires an air/heat exchanger system which runs
continuously using AC mains and also careful additional ventilation of
bathrooms and cooking areas. Both my daughters houses each about 1500 sq.
feet per one floor plus a 'full basement' are built to this standard are
electrically heated and are very economical and comfortable.
Efficiencies of up to 80% heat recovery are claimed for the air/heat
exchangers but personally I doubt if that is true over a wide range of
temperatures. Not having an air exchanger in this older more 'leaky' and
less efficient house am not familiar with their operation in detail. They
do
produce condensate which is drained away by a tube and do need cleaning of
the filters and heat exchanger core fairly often.. (How much water vapour
does a human breathes out during a typical night? A litre or two?
By the way, misunderstandings persists about not allowing the house
humidity
to get into the outer walls of older homes. Consequently one hears a lot
of
nonsense about 'Not being able to keep paint on my house", among older
folks
who built houses in the older traditional way. As to why paint blisters
and
peels on the outside lapboards of a painted house. What's happening is
that
without vapour barriers and or adequate ventilation moisture condenses as
it
meets the cold 'within' the exterior walls and then pushes the paint off!
Houses finished with permeable stain permit that moisture, some will
always
occur, to 'breathe' out through the walls. This approach has worked for us
in the two houses we built and have lived in ourselves since 1960. Some
older houses that have been covered over with nice looking? but
impermeable
siding, such as vinyl, have suffered some rot within the walls! My
neighbour
had to replace most of one end wall of his less than 25 year old house!