"Cicero" wrote in message ...
"The Natural Philosopher" wrote in message
...
N. Thornton wrote:
(Alex) wrote in message
. com...

I have installed rockwool insulation blankets under the floor and I am
now experiencing some worrying problems with condensation as the
insulation itself gets very humid at times with water dripping onto
the DPM laid on top of the underfloor (no concrete).

The floor is made of 18mm plywood nailed on top of the joists. The
insulation is placed between the joists. The crawling space is about
600-800mm deep.

I am thinking of reducing the crawling space (and so the volume of
air) so that the existing ventilation will be more efficient.
Someone mentioned to install a vapour check membrane underside the
plywood (floor).
Will the above work? Any other suggestions?

Thanks

Alex


remove the rockwool, that was a design error I'm afraid. More air
bricks may help to some extent, but you still need to remove the
rockwool as it prevents air movement round the wood.

NT
--------------------
I disagree.

I would say the correct thing to do would be to isntall a vapour barrier
above the insulation, and ensure decent insulation.

Its no different from an insulated loft, upside down really.

the difference is that the underfloor void is constantly wet.
If or when any damp gets past that barrier, as IRL it will, it is then
trapped, and rot will occur. The floorboards will be nailed thru the
barrier, lots of holes.


-------------------
I think that rockwool isn't the best insulation to use in this situation.

I used 2" polystyrene slabs wedged between the joists. This was suggested
and approved by my local Building Regs people and by the company who
supplied the polystyrene. Building Regs suggested that there should be no
gap between the insulation and the under-surface of the floor. The company
who provided the polystyrene suggested that a 1/2" gap would be helpful in
case of liquid spillage from above. The suggested 1/2" gap was to ensure
that any spillage would drain away safely past the insulation.

I'm not sure what 'The Natural Philosopher' intended when he said,
".............draught proof below it ............". It's actually
important to maintain the existing ventilation (via the airbricks) under the
insulation to prevent condensation / rot etc.

Cic.

expect rot. Dryness and air movement are the 2 things that avoid it.


Regards, NT