Terry wrote:

"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.

Nope.
Most of the attic boards are sound.
The problem isn't condensation, but water getting under defective/slipped
tiles, running down the tar-paper, and pooling against the 'gutter' of
tar-paper that's against the bottom board.

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

Unfortunately, not.
It's plasterboard, with no barrier that I am aware of, just 150mm of
loose glass-fiber, with boards on the top.

Is there special paint that can be used instead, on the insides of the house,
and then painted over with normal magnolia/...

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

I really doubt that there is this much.

Would simply leaving the bottom board off the attic, and replacing with
a shorter one, so there is a small gap work?
(obviously there would have to be a carrier over this to keep the tar-paper
off and provide a vent.)

If the roof was insulated with polystyrene or similar boards on the top,
would this not greatly help?

There is only light mold on the inside of the timbers, they are fundamentally
sound, but it should be fixed.

attic that allows warm and therefore humid air to get up there; or is there
anything vented into the attic that should not be?

I don't really think so.
There is a recent 3" hole, for cabling, but this is not a recent problem.

This house was rebuilt from an old stone cottage by a builder for his
mother, who subsequently died.
I suspect it was not built with longevity in mind.

Thanks everyone for the comments.