"Tim Lamb" wrote in message
...
In message , The Natural Philosopher
writes

Any pointers to how others have approached this problem?

regards
--
Tim Lamb
..
Why don't you look at how we build wood frame houses in Canada!

These commonly have 2 by 4 or 2 by 6 wood stud walls which are heavily
insulated.

There is much emphasis on a well sealed non-permeable vapour/air barrier on
the 'inside' or warm side of the wall structure, including careful vapour
sealing around electrical outlets etc. in exterior walls. The most rigid
standard, R-2000 also requires the use of an air-exchange which exhausts
stale air, brings in fresh air and in the process recovers much of the heat
from the outgoing air.

On the outside of the wall underneath any 'cladding', including brickwork
which here is rarely used structurally, the use of a permeable 'building
paper' or product such Tyvek is normal/required. Outside finishes can be
wood siding, vinyl siding, occasionally metal and more recently a product
that looks like wood clap-board (lap-siding) but is made of cement. Very
occasionally stucco. See note:

One other thing that I recall for this particular climate (eastern maritime
Canada) which is wetter and generally colder (for longer) than most oft the
UK, is that 'not more than one third of the total insulation should be
inside the vapour barrier. The reason being to not allow warm and therefore
moisture laden air to permeate into the wall and condense at some point
within it causing wet insulation and/or rot and mould.

We have used vapour barriers and Al. foil in the walls and insulated
ceilings of both house we have built and lived in since 1960. Adhering to
the principle and standards espoused by CMHC (Canadian Mortgage and Housing)
has certainly been worthwhile. No rot, minimum draughts, low maintenance,
little paint peeling etc.

BTW it's wise also make sure of sealed ceilings and a well ventilated attic;
failure to do so can cause attic condensation and roof rot! IIRC the minimum
'distributed' venting is 3 sq.feet per 1000 sq. ft of area, 0.3% (by area
not volume). Most house have much more than that, with frequently or
continuously vented soffits and/or gable-end and/or roof vents.

Note: A neighbours house one year older than ours, later had some sort of
sprayed on coating with a slightly rough 'stucco like' texture instead of
stain or breathable-permeable paint. It was applied onto the conventional
wooden clapboard (lap siding). Once completed the previous owner claiming
that he had solved the repainting problem for life. He's dead and gone, rest
his soul.
But the present owner reports that the sprayed on finish is cracking and
peeling possibly due to moisture finding it's way out through the walls? I
always wondered about the validity of the inside vapour barrier since
original owner did much of the building himself; as did we all in those
days! Present owner reports some evidence of mould in a few places in some
walls. Also the slightly rough finish gets grimy, suggesting that even if
it survives the house exterior will have to be repainted anyway.

Our house has pine clapboard siding and again this summer will need
restaining (always use a permeable stain not paint) and some repainting of
the trim. This will be for about the fourth time in 36 years; I will most
likely again do it myself (age 72) using a couple of trestles and planks for
most of it. Happy to report that this house passed insurance inspection
recently and the addition of a couple of requirements will reduce the annual
insurance premium somewhat.