On 2007-02-16 16:25:59 +0000, "Mikeyboy" said:

The existing walls (2 sides, rear) are part of the house - it is based
on an original Victorian conservatory. Nothing new is planned, merely
updating of a rather out of date design. Are you saying that the dwarf
walls won't add to the heat-retaining qualities? Even if insulated to
the max?

They will do, but calculate the areas and heat losses using U values
for the surfaces

You can find tables of U values or programs on radiator manufacturer
web sites or
in the Approved Docs to the Building Regulations.

The calculation for a given surface is to multiply the area in square
metres by the U value and
the temperature difference. When you are doing this for calculating
radiator sizes it is
typical to assume -3 degrees outside and 18 or 21 according to taste inside.
Clearly the larger the U value the worse the insulating properties.

Out of what you have, it is likely that the largest heat loss will be
the current glass because it is
single and has a very large area. If the existing walls are single or
double brick with no insulation,
then they will be next, followed by the floor.

Practically, you probably wouldn't do anything about the floor unless
you want to dig it all up, put in a sheet
of polystyrene foam 100mm thick and concrete, or create a floor above
the existing, on joists, insulate it and board over that.

You could add dwarf walls insulated to modern standards and make some
difference vs. having them as all glass.
However, unless the area is substantial, the effect will be minor in
the context of the overall room. that's why I said that to make a
large overall difference you would need to have these walls larger as a
proportion of the whole and then you run towards being outside the
definition of a conservatory and subject to Building Control.

Certainly the type of glass is the one to go for first.

If you don't mind losing some overall size, you could fix studs to the
existing walls, put in Celotex sheet (has 3 times insulating properties
of glass wool for a given thickness)and fit plasterboard over that.
This would take you to modern insulation standards for walls. It is
likely that this would be the second most significant loss of heat
after the roof and glass walls and door.

Whichever way, you need to do the sums to know what you are dealing with.