Should We Demonise All Cavity Wall Insulation?

Contextualising the argument against Cavity Wall Insulation

Whilst we completely acknowledge that wet cavity wall insulation causes a number of problems relating to moisture transference between the outer and inner leaf, potential penetrating damp and even a secondary condensation damp problem due to the reduced thermal value of a wet wall, we reject entirely the idea that even dry CWI causes problems and yet we are now seeing CWI blamed almost entirely for every damp problem encountered. Scare mongering has always been a great marketing tool but this claim makes no sense whatsoever.

Checking for condensation damp

We have encountered hundreds of condensation damp problems and statistically the problems of cold surface condensation are always worse in solid walled (poorly insulated) properties, the process for identifying primary cold surface condensation is quite simple.

Failed cavity wall insulation

Testing for moisture at depth rules out penetrating damp

We test for moisture at depth in the masonry to rule out penetrating damp and a secondary condensation damp problem caused by reduced thermal value in the building fabric. We record dew point temperature and also record wall surface temperatures to see if wall temperatures are at or below dew point temperature, if it is then this proves that you have an active condensation damp problem.

Proving that CWI is a problem

The same diagnostic process applies to cavity walls and if testing for moisture at depth in the inner leaf of masonry rules out penetrating damp and if CWI is installed then it is not causing a problem. I have recently read claims that even voids in dry CWI ’cause’ condensation but this is a marketing claim rather than being an actual fact. The argument is that internal surface temperatures are cooler (Possibly below dew point temperature) where the void in insulation is to be found. This is absolutely true but the whole wall would be at the same temperature (Possibly below dew point temperature) if no CWI was installed. All this really proves is that the CWI is having a positive effect on the wall surface temperatures where there are no voids.

Some home owners even had CWI installed to help mitigate for cold surface condensation issues as well as to reduce heat loss and indeed it helped and is continuing to help in many many cases. We are we not suddenly  going to reject the idea that improving wall surface temperatures is a significant factor in reducing issues of cold surface condensation.

Nonsense  statements made about cavity wall insulation

A mathematical relationship exists between ambient temperature (Ta), dew point temperature (Td) and relative humidity (RH), if:   Ta is = to Td then RH equals 100%, directly impacting on one value will affect other values. I recently read that CWI causes an increase in internal temperature and a subsequent rise in RH; this point was given in explanation as to why even dry CWI can cause condensation. Again, this is wrong and in fact the reverse is true, an increase in ambient temperature results in a decrease in relative humidity because warm air can hold more moisture than cool air. Generally speaking we wouldn’t even agree that CWI results in an increase in ambient temperatures because most occupiers do not suddenly take to turning up the thermostat on having CWI installed. What actually happens is that they generally have heating set to the same comfort levels but use less energy in maintaining those levels. It is rather simplistic to say that all recipients of CWI now run with higher internal temperatures in their properties so technically there would be zero effect on internal RH levels.

The single biggest direct impact of having dry CWI properly installed is that it raises internal wall temperatures above dew point temperature and therefore reduces the risk of cold surface condensation damp. If it is not inherently waterproof and if the potential exists to transfer moisture across the cavity then problems can occur but the issue needs to be contextualised and it has to be recognised that marketers are now latching on to the anti CWI campaign and these are quite often the same people that installed the product. It would in our opinion be foolhardy and unnecessary to embark on a National campaign to remove all CWI without first gathering evidence that it is actually causing a problem. Visual evidence of damp and decorative spoiling caused by damp does not prove that CWI is the cause of that damp.

So how common are cavity wall insulation failures?

As an interesting aside to this piece and perhaps to underpin our point… I recently received a telephone call from the founder  member of CIVALLI, the cavity wall insulation victims alliance. It was explained to me that BBC Wales had done a piece on cavity wall insulation failures, which had been picked up by BBC East Midlands, who also wanted to do a piece on the alleged high levels of cavity wall insulation failure. Unfortunately, the fly in the ointment was that CIVALLI didn’t know of any failures in the East Midlands and thought that I might be aware of a ‘victim’ to help validate the piece. I explained that I knew of no ‘victims’ and also that I thought the BBC Wales X-Ray piece was in my view, an irresponsible piece of journalism that made no sense of the facts presented. I’m not interested in sensationalist news stories, I’m interested in facts and evidence and my personal experience is that cavity wall insulation failures are not as common as CIVALLI would have us believe; perhaps the fact is illustrated by virtue of the fact that they were not aware of a single case of failure in the East Midlands that could be used to support another sensationalist news story.

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  • Brian Fish


    We live in the North East of England and in severe cold weather conditions do suffer from condensation and mould after having CWI installed. I would suggest your assumptions are equally unfounded and the reality suggests that the system is not fit for purpose and will fail even more in the future.

    If cold bridging exists in any form the CWI also does not allow the surfaces to breath the way they have done for decades, therefore the RH would rise above the normal previous experienced levels and cold bridging would hit the Td.

    • Joe Malone

      Hardly unfounded Brian, I’ve tested hundreds of properties for moisture in the masonry after having CWI installed and the fact is that it is not causing moisture levels to rise in the underlying masonry. Moreover I’ve inspected hundreds of wall cavities with a borescope and thermal imaging and the only problem we commonly see is insulation voids due to poor installation.

      What ‘reality’ suggests it is not fit for purpose? Some of your post makes little sense. Are you suggesting that inhibiting wall breathability causes internal relative humidity levels to increase? If you are then the suggestion is nonsense. You could equally argue that current air tightness standards for buildings are causing high humidity but we build energy efficient properties now mechanical extraction needs providing to account for this, ideally in the form of heat recovery fans. Masonry, and indeed, floors, will to some small degree act as a moisture buffer, absorbing and releasing some humidity over time but in reality this has little or no impact on internal humidity levels. The most common form of CWI, blown fibre, is in fact breathable so again, this point highlights that your comments make little sense. I hear a lot of talk about the ‘reality’ of CWI and I’ve yet to see anyone provide any proof that CWI is causing widespread issues.
      Perhaps you could explain your ‘cold bridging’ point as it relates to CWI, because again, your comment makes no sense?

  • G

    We live in the Midlands and have issues with the damp and mould after CWI. Apparently our home should not have had this injected into the cavity and installation is patchy. Warm air condensing onto ‘cold spots’ where there is no insulation has resulted in mould growth and dampness. The presence of this insulation would likely cause further issues unless the product was removed (i.e., corrosion of wall ties etc),
    From our understanding, the removal of this product is an invasive, noisy and intrusive process which can cause damage to brickwork and so, decisions for removal should not to be taken lightly.
    Cavity wall Insulation is not suitable for all homes with a cavity and in some cases, installation has not been done correctly by unscrupulous installers.
    Perhaps you could reflect on these circumstance in your argument to give a broader view about the issues of CWI.

    • Joe Malone

      Thank you for your post Gertrude though again, it seems obvious to point out that your post is littered with words like ‘apparently’ and ‘likely’ but do you actually have any proof beyond your anecdotal comments? If you read my posts properly on CWI you’ll see that I have reflected on the broader issues and presented a balanced argument. CWI does not cause cold spots, rather the cold spots remain where inconsistent fill has been achieved. Yes, this is a common problem but the whole wall would be a cold spot if CWI were not installed. You say the installation would ‘likely’ cause further issues, but this is not the case at at all, in fact it is unlikely that it will cause issues and provides a valuable function in the majority of homes. The primary risk is to properties in exposed locations; in particular those that have blown fibre installed, which is not inherently waterproof. We’ve inspected enough wall cavities to form a pragmatic viewpoint on this. Wet CWI can cause corrosion of wall ties, but again, wall tie corrosion was a well recognised problem long before the current fashion for blaming all internal damp on CWI. Ferrous wall ties or those with a poor quality galvanised coating will perish anyway, and would have done so even without wet CWI installed to the wall cavity. The problem is well recognised and has been for years and at no point have the BRE or anyone else for that matter, suggested that CWI is to blame. What about non-ferrous wall ties? Are you suggesting that CWI will cause those to fail too? Similarly you appear to have a poor understanding with regards to cold surface condensation… what has ‘warm air’ got to do with anything? Warm air holds more moisture than cold air, so if the property is warm then you reduce the risk of condensation. You’re right in one respect though, a decision for removal should not be taken lightly, unless you have proof that the CWI is wet. The mass hysteria and blame surrounding alleged CWI problems and the industry springing up to correct a problem that rarely exists is all completely unnecessary and rather like the damp proofing industry which sprang up en-masse to treat widespread rising damp, another problem that rarely exists. Perhaps you could reflect on these circumstances in your argument because it may be difficult for you to accept but we provide a truly independent viewpoint, whereas you clearly have a vested interest in blaming an industry for your damp problems. This is despite the fact that this alleged CWI issue is very easy to prove or disprove, but you choose to rely on rumour and anecdotal information with regards to what has caused your damp. I say this time and time again, if you have any evidence that CWI is to blame for your problem then please share it?

  • Peter Keig

    Wall insulation should only be installed if adequate ventilation rates are maintained throughout the property post-insulation.

    If the cavity is filled, infiltration rates reduce and indoor generated water vapour struggles to diffuse through the inner leaf and escape to the outdoors via the cavity.

    • Joe Malone

      Peter, I agree with the point you make about ensuring adequate ventilation is made but the rest of your post makes little sense. Infiltration is permeation of a liquid into something by filtration. You are therefore suggesting that CWI has an impact on the degree by which humidity is controlled and managed by permeation into the building fabric. In fact blown fibre CWI is permeable and allows air flow and vapour transfer across the wall cavity. It has little or no impact on the permeability of the inner leaf of masonry. In general terms wall permeability is so low anyway as to have almost zero impact on humidity levels within the property.

  • Peter Keig

    Joe, infiltration is the term used to describe outdoor air that enters the home through gaps in the building fabric. The opposite is exfiltration. EPS CWI has an effect on the ability of the inner leaf to shed diffused moisture into the cavity. Fibrous CWI has an effect of the ventilation in the cavity, and once wet increases the thermal conductivity of the wall. Hence BEIS pushing to find a solution to current wall insulation problems that are increasing CO2 emissions not reducing them. You are incorrect in stating that ‘wall permeability is so low anyway as to have almost zero impact on humidity levels within the property’. You need to look at the appropriate BRE and academic research on moisture buffering.

  • Geoff Holden

    I have a 4 bed detached house in Bury, Lancashire. It was built in the late 80’s with some cavity wall insulation ( the insulation is part of the breeze block. A company is recommending that we have have the cavity filled with Supafil CarbonPlus Cavity Wall Insulation. I see that you say you dont recommend blown fibre. Is there something that you think would be a better alternative.

    • Joe Malone

      Yes, blown polystyrene beads. They flow better into the cavity and there is far less chance of voids in the cavity fill. Additionally it is inherently waterproof.

  • Are you saying we should forget the breach of dutyrequirements of BBA , agrement cert. and any actual loss to the homeowner?
    And the vast amounts of monies paid over to these companies following insulation into cavities/lofts. No interest by them of fitting cavity brushes or ensuring free flow of air !
    The assessment of the property means they have deemed suitable for insulation. No excuse now if found not suitable e.g. dpc ,debris in cavities a d other cumulative effects. Impossible to defend.

    • Joe Malone

      Hi Mike, not at all and I’m struggling to understand how you could come to that conclusion or question within the context of the blog. It’s a technical blog that clearly explains the issues. Let me ask you a question though… what loss to the homeowner? Do you have evidence of such losses? I have consistently been clear that a large number of blown fibre cavity wall installations are not properly installed. Typically with poor fill and bonds in the insulation; in a couple of cases I’ve found there was no insulation installed despite the homeowner paying for it. Does this fact in itself mean there would be consequential loss or damage to the homeowner? No, of course it doesn’t. It does however mean that there has been a contractual breach to provide the homeowner with what they paid for. The bigger issue is to whether these poor installations are causing consequential damage and loss to the homeowner and my considered opinion based on hundreds of detailed surveys are that this is extremely rare and the vast majority of well installed CWI installations are doing what they were intended to do.

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