Andrew Gabriel wrote:
In article ,
The Natural Philosopher writes:
I think we know know why...the real discussion issue is 'what is the
simplest way to fix it?

Yes, but at two levels.

The first is what can I do quickly (like in half a day) to dry out
the loft and allow the rafters to start drying. I won't be able to do
a long-term fix until later in the year.


Open the loft hatch mebbe and let some warmth in there, the ventilation
will do the rest.


I might try something with the dehumidifier, such as having it upstairs
and discharging into the loft, but I need to do some measurements to
make sure it extracts enough moisture so it doesn't make the situation
worse, and I didn't have a humidity meter on me when I was there last
time. (Unfortunately it won't work in the loft as it's too cold for it.)

Second is what's a proper long term fix (which isn't too much work of
course;-) This requires proper diagnosis, since fixing the wrong
problem won't do any good.
Somehow you need a vapour barrier in there if the insulation is as good
as it seems to be.

And it really is old lah and plaster.

A lot depends on the rooms below. A simple fix is to reline below over
existing with foil backed plaster board, and skim or use lining paper to
finish off. and repaint..

I am not sure about fixing from above, but lifting insulation and laying
plastic sheet over the lot and re laying insulation might work as well

Or even strips of plastic laid between the joists: its not to make it
watertight just to cut it down till the existing ventilation can cope.



It looks like moisture through the lath and plaster might be significant.
So, what's the best way to do this? I could probably roll back the
insulation to get to the laths (it runs between the joists, and then
another layer across the top of the joists).

Could I simply buy some of the thinner damp proof membrane and lay
this over the laths, or is there a better material? I have a large
roll of non-breathable sarking which might work for this.


Sounds ok to me..see what others say.

Can it go up and over each ceiling joist? Cutting it to fit between
the joists would leave long unsealed stretches along the joist edges,
defeating the object of trying to seal. However, if it goes up and
over each joist, the joist tops will be sealed cold spots (with only
one layer of insulation over).

As I said. major reduction is the game. not 'sealing' ..think of it as a
path with a leaky plug and a dripping tap..as long as you are getting
rid of it faster than its coming in, it wont end up in the rafters.

Anything will do. celotex is foil baked as is fooiled plasterboard.
Could cut strips of that and simply flop them down between joists.. betweem

Another option is replacing the ceilings, but taking down two large
lath and plaster ceilings is not something I like the idea of, and
overboarding always seems to me like a bit of a bodge.

It isn't really. I've got bits of doubled up plasterboard here..its
standard for extra sound insulation in many places.