"Andy Hall" wrote in message
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100mm of foam in the walls of a 70s house is not very likely.

Not as built but the walls are generally of an easily fillable kind and more
and more are being done so with the available grants.


If
there is no insulation in the walls as is quite likely, then the walls
certainly dominate in comparison with the difference between 200mm and
400mm of insulation in the roof.

Agreed.
But under the proposed ODPM scheme the walls would usually have to be filled
before either the property was sold or other improvements made anyway.


Depending on the dimensions, the walls may well still dominate even if
they have some insulation.

Not for a bungalow assuming it has some form of rectangular shape. Of
course if it has large 'wings' then the walls do come more into play and may
dominate.