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.

24 responses to “Should We Demonise All Cavity Wall Insulation?”

  1. Brian Fish avatar
    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.

    1. Joe Malone avatar
      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?

  2. G avatar

    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.

    1. Joe Malone avatar
      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?

  3. Peter Keig avatar
    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.

    1. Joe Malone avatar
      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.

  4. Peter Keig avatar
    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.

    1. Joe Malone avatar
      Joe Malone

      Weirdly, I missed this comment all that time back, but would respond with the following…

      Hi Peter,

      I’m well aware of the claimed effects of moisture buffering but critically, this is related to materials with a high buffering capacity. Bricks, the material with which most solid walled properties are constructed do not have such a high buffering capacity. In any event, when you consider that effective mechanical extraction in the bathroom would be aimed at say, 10 air changes an hour, the effects of moisture buffering are inconsequential.


      Joe Malone

  5. Geoff Holden avatar
    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.

    1. Joe Malone avatar
      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.

  6. Mike lea avatar
    Mike lea

    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.

    1. Joe Malone avatar
      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 voids 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.

      1. Gaz Smyth avatar
        Gaz Smyth

        Hi Joe, you seem very knowledgeable about cavity wall insulation but having suffered from failed CWI myself and had it removed (had become saturated), I have spoken with a lot of people suffering the same problems. Property unsuitability seems to be the big problem within the north-west where I live and also south wales, which is particularly badly hit. However, given that you’re located in Zone 1/2 (Nottingham) on the UK wind driven rain map and most surveyors work reasonably local to their office, I am not surprised by your comments that the west midlands is free of widespread CWI issues. Local surveyors know their local patch better than anyone. However, I would suggest if you perhaps do a few hundred surveys along the north-west coast of England and down in south wales. I think you will find a lot more evidence of CWI failing on a more substantial scale. This may then give you good reason to either revise some of your CWI articles or perhaps write a new blog.

        1. Joe Malone avatar
          Joe Malone

          Hi Gary,

          Firstly, I don’t mention zone 1 or 2 or the West Midlands, so you have made assumptions that are incorrect. We carry out surveys right across the UK and I’m more than aware that properties in exposed locations may be those more susceptible to penetrating damp. What is interesting though is that CIVALLI want to paint this as a UK wide problem, not confined to the more exposed locations; even contacting me to ask if I knew of any ‘victims’ in the East Midlands. I’ve done many many surveys along the north west coast of England and in Wales, on many occasions with the home owners thinking failed cavity wall insulation was the cause of their damp, and on each occasion it wasn’t. What you are essentially doing is linking exposure maps with failure rates, but extending your theory beyond nothing more than your own experience, of which I have no evidence, and of course your anecdotal conversations with ‘a lot of people’, again, it goes without saying that this isn’t evidence. I’ve also had conversations with a ‘lot of people’, who appointed us to investigate the matter; all initially believing their CWI was the cause of their damp, and in each case they were wrong. Of course, it makes no difference to my business whether we do or don’t diagnose that CWI was to blame, we simply have the tools and experience to properly investigate the matter, and we get paid for our conclusions no matter what they are. So our findings are truly independent and not driven by homeowners who think they may be able to claim compensation for their damp problems, or indeed driven by an industry created to remove CWI, usually at vast expense.

          However, you think I should write a new blog, detracting from a blog, which is based on a mountain of physical evidence and site testing because you’ve spoken to a lot of people with the problem. Some time back I offered my services free of charge to CIVALLI, after their claims that some home owners suffering from this problem can’t afford the survey work. Despite this lack of affordability, they always seem to conclude that the CWI is to blame. Of course, they never took me up on my offer, in my view because they were afraid the findings wouldn’t support their position. Time and again, I have asked those who claim to have failed CWI to send me the proof but of course it never materialises beyond vague claims, because an industry is now being created on the back of this alleged and over hyped problem. I don’t write blogs based on anecdotal evidence or vague claims Gary, so no, I won’t be revising the blog, or writing a new one to alter my position on the subject. Kind Regards.

          1. Gaz Smyth avatar
            Gaz Smyth

            So large swaths of south wales with housing estates in the valleys that have properties suffering from severe dampness from CWI (insulation being physically removed and found to be saturated) is just dampness caused by other issues? Why would a Welsh MP get involved? I partially agree with your comment about condensation not being caused to internal wall spots where there are cavity voids present. However, it is not a complete marketing claim as mould does get caused and this can be seen around window reveals, wall/ ceiling junctions etc where these areas become colder and exacerbated once CWI installed. I bought a IR thermometer and I saw for myself the difference in temperatures between these areas in my house.
            .The zone 1 to 2 reference is in relation to where your office (assumed) is located and therefore you must work in an area that does not suffer from severe/ very severe wind driven rain, and hence the properties are not a higher risk of moisture penetrating a cavity filled property.
            I recently had a survey carried out a surveyor says that he only works within a 25 radius of where he lives so he maintains good local knowledge. I assume you work across the UK because you are an expert and/or like to travel, unless you are a national company with multiple offices.
            I don’t believe CWI failures are endemic throughout the UK but various areas such as in the north west, south wales and in Scotland are seeing large CWI extractions taking place(e.g. local authority housing estates). I agree there are a lot of people trying to jump on the claim band wagon, but making disparaging comments about CIVALLI, a volunteer group who are speaking with people suffering from the effects of CWI (photos of damage documented on social media), doesn’t help anyone. I can’t speak for CIVALLI but perhaps offer your services again and visit some particularly badly hit properties. I think CIVALLI and others would also be interested for you to publish some figures of CWI surveys you have done and a % summary of findings.
            E.g. dampness/ internal damage caused fully or partially by the CWI being present or completely unrelated to it and what was the actual cause. If you could include numbers of your surveys by region, that would also be very insightful as saying you have done ‘many many surveys’ is like the claims companies saying there are ‘many many CWI failures’ out there.

          2. Joe Malone avatar
            Joe Malone

            Gary, you’re welcome to post on here if you have anything useful to contribute beside anecdote and argument, but again, this forms the content of your second post, though I will deal with a number of your points.

            1. You still state that large swathes of properties have suffered from damp due to CWI. Where is your evidence from the survey work done on these properties?

            2. MP’s tend to get involved due to political pressures and know nothing about technical problems in housing.

            3. You contradict yourself; agreeing that CWI doesn’t cause cold spots, but then stating it causes mould. According to you, CWI doesn’t cause cold spots where voids are present but causes them around window reveals. Please explain the mechanism for this illogical claim?

            4. You bought an IR thermometer and noticed temperature differences… So what? This proves nothing and you’ll always find temperature differences whether CWI is installed or not. We use a thermal imaging camera that cost many thousands of pounds and yes, this may show cold spots where CWI has not been properly installed, but this doesn’t prove that the internal leaf of masonry is wet because moisture has transferred across the wall cavity, and neither will your IR thermometer.

            5. You spoke to a surveyor who works within a 25 mile radius and therefore this rule applies to me??? I was recently in the Isle of Wight, Cornwall, Southend, Wales, Manchester, Leeds, Newcastle, York, Devon and London. There is a reason some surveyors work within a 25 mile radius and it’s because they’re valuation surveyors and their PI insurance increases considerably if they work outside that 25 mile radius. We’re not valuation surveyors! I also give talks Nationally for the RICS and this year am speaking at their Roadshow at multiple venues across the UK and Ireland.

            6. I’ve made no disparaging comments about CIVALLI beyond stating the facts. I’m sure they’re well meaning but personally I think their involvement is misguided. There’s a great irony here, you think I should research and collate statistics for a problem that allegedly has already been proven, and that’s the problem, it hasn’t! The key claim here is that CWI causes internal penetrating damp by allowing moisture to transfer across the wall cavity. Yes, blown fibre has the potential to do that, but it very rarely does, and any claims that it causes internal condensation damp where internal masonry is found to be dry at depth, are just nonsense.

            7. To respond to a blog you feel I should collate years of survey work and produce statistics for you? No, I won’t be doing that Gary but suffice to say we’ve looked in hundreds of wall cavities in damp properties and have only ever found two cases where the CWI was wet. We’ve found numerous cases where CWI has been poorly installed, in fact most blown fibre systems are poorly installed. However, this doesn’t mean that they cause internal damp. The bandwagon is already rolling Gary, and that pre-supposes that the evidence is already in place so it should be very easy for you to provide that evidence, not anecdotes relating to your own experience and discussions with people you know.

            Kind Regards

  7. Paul Brimstone avatar
    Paul Brimstone

    We have two 1965 bungalows next door to each other on the IoW. One has no CWI, and does not suffer mould. The other has the cavities filled with polystyrene balls and will acquired mould in a few days, weather dependent. They have identical build, identical ventilation. That’s fact, not opinion. Additionally, the polystyrene balls are a nightmare. If you make a hole in the wall for plumbing, it’s hard to keep them from flowing out by the million. And worst of all, any electrical cables running in the cavity are literally dissolving slowly. Pull one out and the outer surface is sticky. Bladdy awful stuff. I’m only here because I’m looking for someone to remove it.

    1. Joe Malone avatar
      Joe Malone

      Hi Paul,

      Your statement may well be fact, but what is also a fact is that this in no way proves that the CWI is responsible for the mould. I take your point about polystyrene beads, which is why we always recommend bonded polystyrene beads.


      Joe Malone

  8. GM avatar

    As an ex-chartered surveyor myself (not of your sort) I am impressed how you defend your learned opinion. The CWI debate is set to continue with the next chapter of government handouts to people who do not fully understand the consequences of their actions (including installers) enticed by the “half-baked” government plans for “climate” issues.
    An excellent blog.

  9. fiona avatar

    Hi joe
    Would a small 1m by 1m void in mineral fibre wall cavity insulation towards the bottom of one end of a wall of a detached bungalow with a solid subfloor be intentional or or not. We were asked it if was solid despite only knowing it was of block and beam type. Would this be a reason for a small void to assist with breathability etc or not.

    1. Joe Malone avatar
      Joe Malone

      Hi Fiona,

      No it wouldn’t be intentional, and this is one of the biggest issues we face with blown fibre CWI; incomplete fill. If there is a subfloor void, then yes, this would need ventilating, but subfloor air bricks would be sleeved through the wall cavity, so that the CWI didn’t block these vents.



  10. Humph avatar

    I live in postcode DN22 (N-E Midlands: driving-rain exposure zone 1 (“sheltered”), though close to the edge of a zone 2 (“moderate”). There is no advice against installing CWI in these zones if the construction of the building is suitable, and in good condition.

    My next-door neighbour has recently has his foam CWI removed due to what we were told was widespread damp/mould on inside walls, He bought this detached 1968 house in late 2022. He had had a full structural survey done, which apparently reported no problems with the CWI

    When recently blown and sucked out by a contractor, some (tho9ugh very far from all) of the foam was found to be damp or, just above DPC level, actually wet.

    Their contractor (who is also a CWI installer) told me that he had advised my neighbours to let the cavities dry out, after which he would re-fill them with insulation beads,

    We bought our own house, also a detached 4-bedroom one, in 1979. It is next to the one mentioned above, and was built by the same builder, also in 1968. CWI foam was stated by our seller to have been installed by injecting the cavities with UF foam in 1972. I don’t know if the neighbouring house was so treated at the same time and by the same contractor.

    In 1998 we had a single-storey extension added to the our house (built under a local authority Building Notice). A section of the original cavity wall had to be removed for this. When the outer leaf of the wall had been dismantled I could see that the foam had been adhering tenaciously to the inner face of the brickwork. The exposed cavity was fully packed with clean, dry foam, which also adhered tenaciously to the inner face of the inner (lightweight block) leaf of the wall..

    Also in 1998, we had double glazing installed (a quality job). I improved the loft insulation by underdrawing the roof rafters. And, yes, I ensured a free ventilation passage from the vented soffit boards on one side of the pitched roof, up and under the ridge board, to the other.

    Part of the 1998 double glazing job was for fit UPVC “roofline” (gutter boards and the vented soffit boards mentioned above). It also included removing several rows of roof tiles and the ageing sarking section of this covering, which is a good quality polyester-reinforced roofing felt. The weathered/eroded bottom sarking section was removed, and replaced by new heavy duty sarking reaching fully down into the backs of the (also renewed) gutters. Anti-bird combing was added. Our fitters commented that this part of their job was very appropriate owing to the 1968 wall cavities being open at the top (CWI being also uniformly visible here).

    In 2004 I installed a 3-speed venting system into the top floor of the house (the unit and ducting being in the loft). One of the extraction inlets is over the stairwell, so helps also with the downstairs air. In addition, we have proper 6″ wall-mounted extractor fans in the kitchen and utility room, and in the downstairs and upstairs bathrooms.

    Over the so far 44 years of our occupancy we have had no problems at all with damp inside our house. This, like our neighbour’s, is of good quality construction for a speculatively-built 1968 estate house. The brickwork of both looks in good condition (including mortar beds and perps),

    So we were astonished by the problems reported by my neighbour, and taken aback by the intrusiveness and messiness (not mention the reported (by the owner’s mother, to my wife at the local gym, £3k cost) of the stripping job.

    I asked the more senior of the two men who had done the stripping about:-

    1. Condition of the galvanised steel wall ties. He showed me camera shots revealing these as still surprisingly sound looking, and not with much in the way of mortar blobs caught up on them. I was relieved, for our sake, as well as that of our neighbour!

    2. The cause of the wetting of the CWI. He seemed to have no idea what could have caused this, because the condition of the brickwork was good, and the foam was mainly dry, and appeared to have been installed competently. I mentioned that the cavities, which, if they are as on our house, are not closed at the top. He did not say if he was aware of this. But he did embark on a list of possible causes of the wetting of CWI, which included, in extreme cases, rotted sarking felt allowing rain water to run through displaced tiles onto the wall plate topping the inner leaf of a cavity wall and thence into an open-topped cavity.

    I discussed this with my wife. We agreed that, if sarking is rotted back/eroded by weathering/birds right back to a point where it allows leaks around the second or third row of tiles, it might allow rain to trickle through onto the wall plate as described above, soaking the CWI and, as this gradually detached itself from the wall inner faces, trickling further and further down the cavity.

    I am not confident enough about the soundness of this suspicion to ask my neighbour if he was advised by the CWI removal contractor to get the sarking felt checked, and replaced if necessary.. He seems a practical and sensible man, He presumably discussed the cause of the problem with his contractor, so he should not need a non-specialist like me to advise him!

    Any informed views on this possible cause of wetting of CWI would be much appreciated.

    My neighbour’s house had at least four owners since our original next-door neighbours, who had owned it since 1978 (when they bought it from the original owner), until 1993. The period from then until 2022 included it being owned by a local businessman who rented it out over several years to a series of tenants. The last owner/occupier before the present one (2022) had the house double=glazed and the roofline done. But he boasted to me how incredibly cheap was the quote that he had finally accepted.

    This is a dilemma for me, I would hate to see them spending another large sum having the cavities re-filled if the source of the original wetting had not been cured. But they do not welcome comments from what they no doubt see as technically unqualified neighbours, and seem to rely on the man’s father and grandfather for advice.

  11. Neil Graham avatar
    Neil Graham

    Not here to prove or disprove but can you please explain due points in a cwi. Surely when water vapour travels towards the outside from the warmer humid air inside, the air condensates towards the outer leaf. Where does that condensation go and is it this what is creating any alleged problems. I don’t understand how modern methods of insulation require vapour barriers but when people have cwi there is no requirement by the installers.
    I have had cwi and am getting a strange tide mark at low level on the external brickwork but nothing on the inside?.

    1. Joe Malone avatar
      Joe Malone

      Hi Neil,

      By your logic, if wet CWI is causing the tide mark on the outer leaf of masonry because it’s saturated, then it would also cause a tide mark on the inner leaf of masonry. Is this tide mark above DPC level? Ultimately, in terms of diagnosis, the dew points through the building fabric are unimportant. The question is to whether or not the CWI has allowed moisture to travel across the wall cavity to then saturate the inner leaf of masonry.

      Kind Regards

      Joe Malone

Leave a Reply

Your email address will not be published. Required fields are marked *