"Christian McArdle" wrote in message
...

So you installed breathable membrane
under the tiles and have eves
ventilation that vents up the rafters
following the roof slant to the ridge
tiles. I read that only breathable
membrane is sufficient as long as the
is an air gap of 25mm; and no eves
and ridge ventilation is required. The
gaps between the tiles is enough to
take away the water vapour.

Indeed. The ventilation provided is
very belt and braces. Personally, I
wouldn't have bothered with most
of the vents and just relied on the
breathable membrane. However,
I'm certainly not expecting the wood to rot
away any time soon!

It has been proven that the breathable membrane is all that is needed, but
Building Control sill insist on an air flow so the eves ventilation and
ridge tiles have to go in. All they are doing is over cooling the house in
many cases.

If they just accepted the membrane all could be done from inside the loft.
Seal up the eves ventilation gaps into the loft. Rip out existing sarking
with a Stanley knife. Install membrane between rafters stapling and using
tape where needed,. Leave an air gap between underside of tiles and
membrane. Another air gap on the loft side of the membrane and then
insulation and plasterboard. water vapour working its way through the
plasterboard and insulation will work its way through the membrane and out
into the outside air via the gaps in the tiles.

That will work, but I doubt they would allow you to do it. Or will they?