then would I need to worry about ventilation at all?

Why? Have you worried about it before? What are you concerned about?


IIRC, the recommended depth of insulation these days is about 200mm
(damn,
mentioned insulation ... IMM's sure to be around soon ? I think my
joists
are quite a bit shorter than that though. I would like to improve the
insulation at the same time, so what's normally done in this
situation?

lay insulation to depth of joists. Lay another layer on at 90 degrees.


One last point on roof felt. My roof is the original 1930's one and
the
tiles sit on the roof frame with no felt. The loft therefore gets very

dirty. One option I've seen is this spray-on stuff that guys come
around
and do for about =A3200 I think.

Oh no.


Another cheaper option I was thinking of was
perhaps stapling strips of rood felt to the roof timbers. Any
suggestions?

I'm not sure why you want to do anything: what problem are you trying
to solve?


NT