Cavity Wall Insulation: Materials and Side-effects

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:

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do folks think and what is your experience?

Thanks!

Kostas

Reply to
Kostas Kavoussanakis
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> What do folks think and what is your experience?

Damp is a known issue. If water is running down the cavity, as happens occasionally, with insulation there it will soak into it and be trapped, causing damp. In the unlikely event that this occurs, one can repair where the water is getting in.

There are some wall constructions that should never be cavity filled. These are bridged cavities and uneven cavities, such as ratbond and rough stone.

Polystyrene is usually avoided today because of the probems its caused in the past.

NT

Reply to
meow2222

what problems does polystyrene cause? should i remove it from my house?

flammable? does something nasty to electric wires (what?) what else?

[george]
Reply to
George (dicegeorge)

George,

The use of Polystyrene 'balls' is common in cavity fill even today - but fibre fill is gaining popularity/

If your house cavities have been filled for a while with 'balls' and there are no damp patches at various spots on the internal walls, don't worry, there are no problems.

Is it flammable - yes. But its unlikely to catch fire in a cavity wall!

Does soemthing nasty to electric wires - no. And its not a normal practice to run cables in the cavity.

What else - If its polystyrene balls, then they just go everywhere if you have to cut into the cavity. If it's the old Styrene injected foam, then that did cause problems with fumes - But its unlikely that you'll have that.

Hope this helps?

Tanner-'op

Reply to
Tanner-'op

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Tanner-'op" saying something like:

It leaches out the plasticiser and makes the cabling brittle, perhaps leading to fires, so no, no real problems there, then.

Reply to
Grimly Curmudgeon

However the plasticisers cause the polystyrene to shrink away from the cable breaking contact. So not a real problem.

Reply to
dennis

Unlikely to happen to with the 'inert' polystyrene balls in cavity fill - as in the original question - even if were in contact with live electric cables dropped down the cavity (which is not normal and bad practice anyway).

And I suppose that even if you covered a cable in the polystyrene balls and left it like that for years (as in some of the early attempts at loft insulation) - then all would be ok (apart from a possible heat build-up from some high current carrying cables). Now if you were covering the cable in expanding styrene foam - then your arguments would at least be bear some weight!

As a matter of interest, could you point me in the direction of the BRE digests that support this argument - or any other document that would for that matter

Ah well!

Tanner-'op

Reply to
Tanner-'op

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "dennis@home" saying something like:

Oh no, not a real problem at all. Right.

Reply to
Grimly Curmudgeon

With sheathed twin-and-earth cable it's not considered to be a problem if the cable remains undisturbed.

Reply to
Andy Wade

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Wade saying something like:

Until somebody goes and disturbs it. That'll work, I'm sure. I mean, nobody every goes and rummages around the loft, do they? I'm thinking about the thousands of houses that have polystyrene loft insulation, not to mention the unknown number of houses where cables do (in spite of tannery smell's assertion) pass through cavity walls filled with polystyrene balls. Then there's the really common technique of dry-lining older houses with battens + polystyrene aeroboard, where the cables are simply led willy-nilly round the back of the new lining, with no thought given to the contact 'tween cable and 'styrene.

After I first heard of this degrading effect, I started paying attention to new and older installations and was quite surprised at the number of places I found instances like those above. Trouble is, you just don't know what's been done over the years and imo, there's a whole pile of house fires waiting to happen.

Reply to
Grimly Curmudgeon

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> What do folks think and what is your experience?

We had mineral wool injected into our cavity walls many years ago. There has been no damp but the comfort of the house was immediate.

Damp isn't absorbed by mineral wool but there shouldn't be damp in the cavity.

Mary

Reply to
Mary Fisher

oh i should be ok then, in the loft today i found old style rubber cables going to a light socket, they were surrounded by sawdust, which is also very very flammable!

I've found mouse tooth damage to some of the wiring, but no electrocuted mice yet!

Ive been vacuuming the sawdust and polysyrene and foam bit out...

Reply to
George (dicegeorge)

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> What do folks think and what is your experience?

Many thanks for all the answers.

Kostas

Reply to
Kostas Kavoussanakis

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Where in the country are you? The risk is higher in coastal areas and the further west you are.

Reply to
Tony Bryer

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 w= ay it is used to produce an insulation product is.

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

This is called capillary traction. The same happens with glass-wool or mine= ral-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 conden= sation.

Believe it or not, most wall constructions are not vapor-proof. In other wo= rds moisture can travel through a wall. When that moisture meets a cold sur= face it condenses - that is called interstitial condensation when it happen= s 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 insulati= on 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 re= sult 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 wi= ll 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 wa= ll, such penetration is not detectable when the contractor inspects the cav= ity. I do not know of any contractor that hoses the entire wall when inspec= ting the cavity. =20

This is likely to progressively saturate any insulation unless it is closed= cell.=20

So be warned.

Reply to
sydley2008

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Mary, have you placed mineral wool in a tray of water ? See what happens, all be it slow.

Reply to
Syd

by many insulation manufacturers.

way it is used to produce an insulation product is.

back to basic school science. If you stand two pieces of glass in water, w= ith a matchstick between one vertical edge, you will see that the water cli= mbs up between the two panes of glass - the smaller the gap the higher it w= ill climb.

, in a cavity or internally is that there is the risk of interstitial cond= ensation.

words moisture can travel through a wall. When that moisture meets a cold s= urface it condenses - that is called interstitial condensation when it happ= ens within a material - the exact point of condensation is called dew point= .

tion and that should have taped joints or holes.

th a vapor barrier unless the product manufacturer states it is not require= d as is possible with closed cell products.

on and condenses on the inner face of the external wall. Which in time can = result in timber rot.

will permit rain to penetrate and run down the inner surface of the externa= l 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 c= avity. I do not know of any contractor that hoses the entire wall when insp= ecting the cavity. =20

It can happen with unVBed CWI, but seldom does.

NT

Reply to
meow2222

CWI inspectors tend to miss key problems...

- Dirty narrow cavity, eg, 15-25 to 35-40mm rather than clear 50mm width

- Corroded wall ties, eg, black mortar combined with wind driven rain

- Brick returns, eg, at random to brace not just openings but outside walls

Corroded wall ties, narrow cavity, brick snots & brick returns bridging cav= ity, black hygroscopic mortar are all problems for CWI.

The idea is moisture may get in, but as it got in - so it can get out. This= is not true in certain cases, some houses aged roof felt has flopped back = against the eaves and dump water down the cavity in addition to normal wind= driven moisture ingress. The problem is water loading builds up and satura= tion can occur.

I recall 2% moisture content of glass wool insulation results in 100% loss = of insulation value. Where cold bridging occurs local condensation occurs a= t those points (typically around windows) which can cause decoration damage= .

The CIGA guarantee is worthless because it does NOT cover damage caused by = Building Defects and any building which is not to current building regulati= on standards is considered to be defective, not compared to when it was bui= lt. So as usual a piece of toilet paper in most instances except where it c= an be demonstrated the installer was negligent in assessing suitability whe= reupon I think they do pay for it to be scraped out of the cavity.

Bonded polystyrene ball insulation may outperform glass wool, never checked= .

If cavities are 35mm the benefits are still present, but quite small. Moder= n cavity wall insulation at build involves thick celotex (far better than g= lass wool) AND usually maintains an air gap so water penetration can run fr= eely down the outer leaf. A common fault then is the insulation separates a= way from the inner leaf, or a gap is left which results in convection - ess= entially turning the insulation's effectiveness into little more than "ware= housed insulation board".

If you are redecorating a room, and you can afford to lose 50-70mm off it, = frankly I would insulate internally with 50-75mm Celotex. It will far outpe= rform CWI in terms of rapid room warmup (and cooldown, more useful in summe= r) and give the lowest heating loss.

Reply to
js.b1

This sounds like a good idea for those of us without cavity walls then? Brian

Reply to
Brian Gaff

cavity, black hygroscopic mortar are all problems for CWI.

not true in certain cases, some houses aged roof felt has flopped back against the eaves and dump water down the cavity in addition to normal wind driven moisture ingress. The problem is water loading builds up and saturation can occur.

insulation value. Where cold bridging occurs local condensation occurs at those points (typically around windows) which can cause decoration damage.

Building Defects and any building which is not to current building regulation standards is considered to be defective, not compared to when it was built. So as usual a piece of toilet paper in most instances except where it can be demonstrated the installer was negligent in assessing suitability whereupon I think they do pay for it to be scraped out of the cavity.

cavity wall insulation at build involves thick celotex (far better than glass wool) AND usually maintains an air gap so water penetration can run freely down the outer leaf. A common fault then is the insulation separates away from the inner leaf, or a gap is left which results in convection - essentially turning the insulation's effectiveness into little more than "warehoused insulation board".

frankly I would insulate internally with 50-75mm Celotex. It will far outperform CWI in terms of rapid room warmup (and cooldown, more useful in summer) and give the lowest heating loss.

Something like this?:

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'm thinking of fixing some to the alcoves either side of a chimney breast, as I'm in the process of decorating anyway.

Main problem is the coving - original 19C and too much trouble to remove. So thinking of taking the Celotex to within 30cm or so of the ceiling and creating a shelf.

Rob

Reply to
RJH

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