I'm just about to get the felt on my flat roof replaced. I mentioned to the
roofer that it would be good to have better insulation.
He has suggested adding a vapour layer and an insulation on the top deck.

Having thought about it, is it going to do any good?
The roof consists of an upper deck with a 'void' of about 18 inches before
the lower surface which I think is made of chipboard.
There is an access hatch to the roof from within the house.
When it is windy, you notice a pretty strong breeze if you pop you head into
the void. Whether this is just for ventilation or whether we need some repairs
done, I'm not sure.

So if there is such a breeze in this space, isn't insulation that is above this
a waste of time?
I would have though the insulation should be in the void although this would
be more difficult to do.

Any thoughts appreciated.

Pete