The question is if there is nowadays better glazing that could be
retrofitted and improve the thermal properties of what is
fundamentally, in my opinion, incorrect construction.

In our house we have an (unfortunately) unheated "sunroom". That' a
room that has three sides exposed, with 2m-tall, floor-standing
windows for walls and a pitched, insulated roof. There is no ceiling
per se, one can see the eaves, but if there was one it would have been
2-2.2m high (no thanks :-)). It is significantly (up to 1.5m) raised
from the ground.

We use this very infrequently, for the expected reasons; despite the
black-out blinds in the summer it can exceed 35deg and in the winter
my stingy heart aches to heat it with an oil-filled radiator (though
it is on at the frost setting). In spring it can be unbearably hot
during the day and still need heating in the evening.

It is double-glazed, with wooden frames and must be 10-15 years old. I
have no simple way of extending the heating to it (wooden floors in
the adjoining room and concrete/terracotta tile floor in the sunroom).

Thanks in advance for any ideas!

--
Kostas