John Rumm coughed up some electrons that declared:

Tim S wrote:
OK...

A poser:

As I understand it, sarking is for windproofing, not water proofing a
tiled roof?

its also a second line of defence against water. (a felted and battened
roof is reasonably water tight even before tiled).

Then, if we install celotex between and under the rafters and therefore
become concerned that we maintain good ventilation above the celotex,
then why not just remove the sarking and let the roof breath through the
tiling? The celotex (at al) will give us our wind proofing...

Patches of my sarking are falling off and I see no evidence of water
ingress in those areas, but I do feel the air moving when the wind blows.

Just a thought...

If you leave it in place, make sure there are some vents at the bottom
of the rafters, and a gap behind the celotex, then you can probably
achieve enough through draft at the top by just cutting away a 4" strip
of sarking near the ridge.


It could be a useful technique on a few blind areas under windows (my dormer
walls are externally tiled too).