On Sunday, May 4, 2008 2:02:30 PM UTC+2, Kostas Kavoussanakis wrote:
I read some recent articles on the newsgroup about cavity wall
insulation. It is not hard to buy the argument for it, esp. at a
reduced price, as subsidised by energy companies.

However, I tried to do some research and came across a claim that it
can cause dampness and also that the mineral-wool product is inferior
and actually the cause of damp:

http://www.telegraph.co.uk/property/...29/pask129.xml

What do folks think and what is your experience?

Thanks!

Kostas

Hi,

You identify an old problem that is not explained properly or not at all by many insulation manufacturers.

Whilst a basic product in itself may be waterproof that does not mean the way it is used to produce an insulation product is.

Take for an example glass - it is both waterproof and vapor-proof, but go back to basic school science. If you stand two pieces of glass in water, with a matchstick between one vertical edge, you will see that the water climbs up between the two panes of glass - the smaller the gap the higher it will climb.

This is called capillary traction. The same happens with glass-wool or mineral-wool.

Another point that most fail to mention is - when you insulate externally , in a cavity or internally is that there is the risk of interstitial condensation.

Believe it or not, most wall constructions are not vapor-proof. In other words moisture can travel through a wall. When that moisture meets a cold surface it condenses - that is called interstitial condensation when it happens within a material - the exact point of condensation is called dew point.

ALL insulation should have a vapor barrier on the warm side of the insulation and that should have taped joints or holes.

INTERNAL insulation.

If you insulate the internal of say a solid wall, it should be covered with a vapor barrier unless the product manufacturer states it is not required as is possible with closed cell products.

If you do not, you will find the internal air passes through the insulation and condenses on the inner face of the external wall. Which in time can result in timber rot.

CAVITY WALL insulation.

The same as above can happen.

Also almost every external wall will have minute cracks etc in it, which will permit rain to penetrate and run down the inner surface of the external wall. Unless a pressure hose e.g. a fire hose is directed square on to a wall, such penetration is not detectable when the contractor inspects the cavity. I do not know of any contractor that hoses the entire wall when inspecting the cavity.

This is likely to progressively saturate any insulation unless it is closed cell.

So be warned.