"David Hearn" wrote in message
...
Our 1930's semi has a roof which is unlined. Consequently the roof is
very
dusty (I think from the old tiles + dirt etc). We have no plans to
re-tiling the roof - but still would like to do something to stop the dust
coming in.

You may have 70 years of dust. I had similar and did a complete clean
including under the ceiling insulation. I have found the rate of new dust
deposition is actually quite low and doesn't really much affect things in
boxes.

As long as you maintain free ventilation in the rafter space stapling a
membrane to the rafters shouldn't cause damp, may actually improve things.

Alan