"Pete C" wrote in message
...
On Mon, 12 Apr 2004 15:32:38 GMT, Ian Stirling
wrote:

I have a roof.
I suspect others may too, so am asking advice.

It's on top of an attic, and has tiles on top of a felt paper layer,
attatched to rotting bits of wood.

The underlaying planks (I'm sure there is a technical term) are sound,
but won't be for that much longer.

Hence, I plan at some time in the not-too distant future to remove all
the
tiles (section by section) the old bits of wood which the
tiles are hung on, replace the tar-paper, with nice thick tar-paper,
and then attatch more wood, and replace the tiles.

If you have rot it sounds as though the attic may not be sufficiently
ventilated. I.e. moisture is getting bottled up/trapped in the attic/roof
space and is condensing on the inside of the cool roof.
Presto rot, mould etc. If you use anything at all on the inside of the roof
it should be a 'permeable' material that will allow moisture to breathe out
through it along with adequate ventilation.
The other question is where the moisture is coming from? All
heated/insulated living spaces should have a non-permeable vapour barrier on
the warm side of the insulation. At an extreme some types of oil based paint
can be used as a vapour barrier but are not ideal. BTW the recommenmndation
in some jurisdictions is that there should be a MINIMUM of 3 sq. feet of
venting, evenly distributed to permit cross ventilation of the roof space
for every 1000 sq. feet of ceiling area. Are there any openings into the
attic that allows warm and therefore humid air to get up there; or is there
anything vented into the attic that should not be?