I was wondering about how you keep the insurance company happy with
ventilation in conservatories. Can you get, say, self opening windows which
don't open far

Are you talking of a conservatory or a room extension leading directly into
the house.
If it is just a lean-to conservatory on the side of the house then insurance
will be no problem.

Re ventilation....was always taught that you should have 1/8th the surface
area of the roof.
Otherwise you could fit extractor fans in the ridge section of the gable
ends and low level louvers or covered openings to let cool air in

--
David Hill
Abacus Nurseries
www.abacus-nurseries.co.uk