On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

--
Martin