Cavity wall insulation is a great way to keep your home warm and cut your energy bills, but there are instances where cavity wall insulation is not the right solution and can actually lead to big problems further down the line.
Why were cavity walls introduced?
Cavity wall properties began to be built in the 1930s as a way of stopping moisture penetrating the external walls. The cavity walls were built by laying two skins of brick parallel to one another with an air space between them. The advantage of this type of wall was that water could penetrate the outer skin of brick, but then when it reached the void there was no way it could cross to the inner leaf, ensuring that damp never made it into the home.
In the 1970s, oil prices sky-rocketed and this saw energy bills increase, so the decision was taken to utilise the cavity for an additional purpose – house insulation. The aim of the cavity wall insulation was to slow heat loss, thereby helping lower energy bills. Today, cavity walls are still a popular building type and it is a requirement within building regulations that the cavity is filled with insulation to help limit heat loss.
Building a property and including cavity wall insulation at the same time is pretty easy, but obviously there were millions of cavity-walled properties built between the 1930s and 1970s without insulation. In the 1980s, a method was developed that allowed these unfilled cavity walls to be injected with insulation and millions of properties have been injected with insulation since.
If you do a quick search of the internet, you will find many people who are dead against cavity wall insulation – the reason for this is that in some cases the cavity wall insulation can cause problems!
Problems caused by cavity wall insulation
There are a few common problems caused by cavity wall insulation that are discussed in detail below:
Urea-formaldehyde was used in the cavity
When cavity wall insulation first began several decades back, a particular type of foam was used that gradually breaks down over the years, releasing a toxic urea-formaldehyde gas. If you have this type of insulation you may want to get it removed since it could have health implications as the gas is carcinogenic. The other problem with this particular type of cavity wall is that as it breaks down it slips down the cavity leaving the top of the cavity insulation free, so heat loss can occur.
The good news is that as a result of modern standards, this type of insulation is no longer installed!
Millions of properties benefit from the energy savings produced by cavity wall insulation, but not every building is suitable. If the building is located in an area of the UK that has high exposure to wind and rain, then cavity wall insulation is probably a bad idea. Remember one of the primary purposes of the cavity is to drain water away from the inner leaf of the brick, but if the cavity is filled, this new insulation can create pathways for water to cross over the cavity and cause damp in the house.
Incorrect property type for insulation
Rogue installers have been known to install insulation in properties that are not suitable, like steel framed and timber framed properties or those with porous bricks that allow the insulation to get damp. We get a huge number of phone calls from homeowners who are unable to sell their property and buyers unable to get a mortgage due to the presence of cavity wall insulation in timber framed properties.
Flood or Fire Damage to Insulation
If the insulation gets wet or otherwise damaged by an unforeseen event like flooding, the insulation may need to be removed. An example might be where the water tank bursts or where there is a chimney fire. Here, replacement insulation is likely to be recommended once the defective cavity wall insulation is removed.
Poorly installed cavity wall Insulation
The final reason is perhaps the most common problem associated with cavity wall insulation and is the most common reason why people look to have cavity wall insulation extracted. If wool is being injected into the cavity and the installer doesn’t take care then there is a high chance there will be gaps in the wall where there is no insulation. This can cause damp, so it may be recommended that the insulation should be removed.
Likewise if beads are injected into the cavity they should always be injected with some sort of adhesive to help hold the beads together when they are in place. Unfortunately this process takes far longer than simply injecting the cavity wall insulation beads without glue, so many installers ‘forget’ to do this as it allows them to race from job to job.
The good news is that cavity wall insulation can be removed with minimal fuss. If suitable/appropriate, new insulation can be injected into the cavity or a completely different type of wall insulation can by used leaving the cavity empty (e.g. external wall insulation).
How can you remove cavity wall insulation?
It is currently possible to extract a range of insulation types, including mineral fibre, expanded polystyrene (beads), and urea formaldehyde.
Where wool insulation needs to be removed, it is sucked out by a large vacuum machine. In the case of glued beads or urea formaldehyde, to extract this type of insulation from the cavity, bricks are removed and the insulation is broken up using a specialist type of machinery. Once the insulation is broken down into smaller parts it is sucked out, similar to wool extraction.
The high pressure vacuum machine is used to suck the insulation out of the cavity, and the old insulation is bagged and removed from the property, leaving the cavity completely clear of any old cavity wall insulation.
If you would like to see a cavity wall insulation removal case study, click on the link below – it goes into more detail of the cavity wall extraction process.
>>> Cavity Wall Extraction Case Study <<<
We have nationwide cavity wall extraction partners who between them cover every postcode, so you if you are interested in getting your cavity wall insulation removed then fill in the form below and we will be in touch. Prices vary depending on the type of insulation that requires extraction and the size of the job – the good news though is that in many cases we can use readily available data to produce accurate desktop quotes without the need to visit the property first.
Cavity wall insulation does work – just not every time
It is worth reinforcing the point that in the vast majority of cases cavity wall insulation is a great way to insulate your home – it is relatively inexpensive and the payback is normally just a couple of years. The truth though is that not every property should have cavity wall insulation installed, so if in doubt always seek professional advice to see whether it is right for your property.
If you would like to read more about cavity wall insulation, see our full guide here.
Extracting cavity wall insulation
Need to remove cavity wall insulation from your walls? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.
If you would like us to find you a local insulation extraction expert, just fill in the form below and we will be in touch shortly!
The use of Urea -formaldehyde has not ceased because of ‘modern standards’ – the formaldehyde gas is a carcinogen!
As it is a foam that hardens, in what way can you suck it out…please do some research before writing.
The trend for ‘free’ cavity insulation’ is a Greenwash. The Government pays for it to go in – raised by inflated fuel bills, then the owners the have to pay for it to be taken out when they cannot bear the dampness that results from stopping the air circulation in the cavity.
Hi, can anyone recommend me a company that removes urea formaldehyde foam insulation.
Spot on.
The author of this blog is clueless about Cavity Wall Insulation. “Fortunately, it is relatively rare that the insulation will need to be removed!” utter rubbish, a simple search in Google will bring up on many forums where house owners have been persuaded by the Government to have this stuff pumped in to their walls, with devastating consequences.
Previous owners of my house had this installed, now my cavity insulation is saturated with water, and the internal walls destroyed, the smell of damp is soul destroying. CIGA who deal with the warranty do not want to know, local Council couldn’t give a sh!t, its my problem not theirs.
I have quotes of £2000 to get this insulation removed. Still debating which of my body part I can sell in the black market to raise the money.
Hi John couldn’t agree more, we now have condensation where there’s was none black mould on other areas, since having this stuff pumped into the walls. our house is freezing in the summer , who has their heating on in the summer, we never did. It is time and money wasted .
Hi John, thanks for the comment. Unfortunately there are some cases where cavity wall insulation is absolutely not the answer, but 13.4 million people have cavity wall insulation in the UK (out of the 26.9m homes) – so obviously it works for the majority! I guess the issue with the internet is most people only use it to complain – if you had it done and it worked fine it would be unlikely something you would shout about on a forum!
Anyway thanks again for the comment and I hope you get it all sorted with all your body parts intact!
The older Urea-formaldehyde used in the 1970s is removable since in most cases it has broken down which makes the process relatively straight forward. Also, since it has broken down, it tends to produce cold spots on the cavity walls – so in many cases it should be removed and replaced to ensure the house is more energy efficiency.
Newer methods of insulation should not cause any damp unless the wall is consistently battered with high levels of driving rain, and the installer SHOULD (although may not) advise against it.
I would strongly disagree with the suggestion Urea-formaldehyde foam is easy to remove.
My reasons for this is that a lot of prep work needs to be done on the property before any extraction takes place……as we use compressed air in the extraction process he foam turns to dust and will enter the property through any little cracks around windows, behind kitchen cupboards where the sink and waste pipes are. The loft is a particular problem.
A little research shows that it is not relatively rare that insulation has to be removed. Especially after the heavy rain last winter extraction firms are having a field day (or year).
My conclusion is that especially with fibre insulation you are taking pot luck with damp, the risk may be as high as 50%.
Installers will not necessarily advise against it because they don’t do a detailed enough survey.
After 6 months my walls are still wet. But apparently, it’s not the fault of the insulation company.
Look up the Daily Telegraph article.
Tony – thanks for your comments. While there is always a risk when you retrofit your property in most cases even with extreme weather the current industry research suggests that problems only arise in a really small number of cases.
The CWI should be backed by a CIGA 25 year warranty to help protect the consumers should issues arise. If in doubt, as the article suggests consult the opinion of independent expert (structural engineer), who should be able to provide advice tailored to the condition of your property.
HI I had cavity wall insulation (rock wool) removed due to damp on internal walls – all along base of the hall -which worsened when it rained . My surveyor advised the retro fittred cavity wall insultation was responsible as outside wall was sited to suffer wind driven rain. I bought the house with the problem and contacted the installers to remove under the CIGA guarantee. They agreed to remove as a good will gesture stating the insulation was not cause of damp but the wind driven rain and porous render would have been too much for the insulation and broke it down. Though inspector later advised me the wool thathad been used was no longer used as it holds water, I was just happy just to get it removed. A month ago the team took it out. After a couple of dry weeks damp got much better we had rain and it all came back. I rang them they came up and looked with a camera advised me some wool was still remaining and they come to take it out. . Though the areas of damp did not relate to areas of wool left when i watched them removing it. I thought my damp problems were over and watched the lower walls all dry out again.i usea little water gadget though i know they are not considered very accurate I thought just by the pattern of readings decreasing show it is drying out. All good till we had raing again and walls looking damp again and all readings back up high. Has anyone had insulation removed and faced these issues ? does the damp go i am trying to understand if I should be contacting the insulation company again or exploring other options and considering my surveyor/home buyers report and the supporing damp survey i also obtained had the wrong cause of the damp ? Help anyone ?
Hi Caz, I know its a while since your post but for you or others reading this, has anybody had a look in the cavity at DPC level? It is quite possible you have mortar droppings, bits or brick that had blown off from the installation, and dirt bridging the DPC. A common problem and one that many installers of insulation do not consider.
Hi, make sure that you have unblocked the air vents which would have been blocked up by the installers. Also install air bricks to the top of the wall as your loft insulation has probably closed off the cavity stopping the drying out stack effect. Ensur you have at least 1 air brick per 5 stretchers. Rising damp is a myth. If the damp occurs onlywhen it rains then install a french drain around your property at least 150mm wide around your property.. DO NOT take advise from people who are trying to sell you a product. I have spent many years aquiring my knowlage and it upsets me that people are still been ripped off by uncompassionate salemen with no construction knowlage.
Dear Cas,
I am in a similar position but CIGA have refused to help, can you let me know what you said to persuade CIGA to help you.
I would just be happy if they are able to provide partial funding to get my installation removed.
Look forward to your reply.
Regards
J
Hi Caz,
I would suggest from what you have said that it would be well worth getting a reliable builder to remove 4 bricks every 1.5 metres along the base of the wall one brick above the damp course. Obviously only in the area affected. I suspect that you have a breached dpc which is often the case (not rising damp as such) if there is debris breaching the internal damp course this would be your problem and by taking the bricks out as described, it would enable the builder to remove this debris. The cavity wall insulation probably didn’t help if it is breached by debris.
This sounds like rising damp Caz, you will need to get someone to look at the damp course layer (DPC) to check it is still performing its fucntion
we have a firm called Vac-Xtract and we remove insulation for a living. I would never suggest anyone ever having their walls insulated unless it was bead.
Caz I am having exactly the same problem you had. Had CWI done 4 years ago for free with a government grant. Now regretting the decision as we are suffering with rising damp as the insultation has dropped below the DPC. The walls are damp and mouldy and my children’s bedrooms are so mouldy which is not good for their health. After the heavy rain , the damp is now awful. We now need to look into having this removed. Where do I begin? Will the company who installed the CWI remove the insultation if I complain or will we need to pay to have it removed as well as having to repair all the problems caused by the damp as well. Various builders have said our property was not suitable for CWI and the air bricks have been blocked. I wish I knew what I know now!!
I have a certificate but cannot find a guarantee as such.
Any suggestions will be appreciated. Many thanks.
Georgina,
If the insulation was installed with a government grant, it should have a 25 year industry guarantee through an organisation like CIGA. In which case it should not cost you to get it removed. Look at your certificate and see if it has contact details.
Regards
Alan
At ExtractUK Ltd, we specialise in cavity wall insulation removal. Yes, you do get a 25 year guarantee (generally not for foam) but if the problems have occurred with the last winters storms the insulation companies and CIGA are more than likely to say they will not cover this under their guarantee, as the guarantee covers workmanship and the product. They will not usually cover if your property has any defects in the mortar. What we are finding is properties that seem to be affected have rubble and debris in the cavity and shouldn’t have been installed in the first place, this should’ve been picked up by the surveyor. Please be advised that the moment you remove a brick, or make any structural changes, you may instantly void any guarantee you do hold.
Hi, bought property 1year ago now, and have damp problem on south facing wall. Previous owners had cavity walls insulated. ( can see the holes that are filled on mortar joints where insulation would have been with injected or blown in). On home report high damp levels were reported, but was told this was now rectified. Internal walls had been re plastered and decorated too. Unfortunately damp has returned. Would it solve problem to remove insulation in cavity on problem wall only, or would this create a cold spot and make problem worse? All other walls seem fine, bar the one with damp. Air bricks have also been sealed . Am keen to solve problems but do not want to create another, as am thinking if cavity is filled all round the house, no air can circulate, and if I remove from one wall cavity only, I will be leaving a void with no air to pass through. Could this also cause dampness if done. I have decided to take this upon myself so any advice would be appreciated. Problem wall has garage on lower half built onto it, so was thinking of removing brick at dpc level every metre and sucking it out with specialist vacuum from suitable hire shop, then refit bricks and repoint. Would this work??? All advice appreciated. I’m joiner to trade, and work for small building firm so am willing to do work myself.
My company would suggest not to have any insulation put in the cavity unless the cavity is totally clean from debris / rubble. Bead however seems to be the most durable of the insulation form and have not come across many problems when this has been the insulation installed. Most of the surveyors that work for insulation companies are not surveyors at all and work on commission.
I was very interested in what people had to say . I had my free cavity insulation (beads) in June last year .This was done through E.ON. I have had appox ten visits since as the beads are all over the utility room. No sooner is one site sorted before it starts coming out somewhere else. I am at my wits end and about to contact E.ON. yet again. I would love to have ALL the beads removed any one got any suggestions?
Hi Lorna,
If you fill in the form above we can provide you with a quote to remove the existing insulation. We can then get it installed properly if you would like – or if you would prefer you can leave the cavity free from insulation.
Thanks
James
I have had the cavity filled with Walltite (Polyrethane foam and it is wonderful – It is damp resistant and twice the uvalue of other insulations
Those with problem areas might try injecting a small area with builders foam, which sets on touching water
Hi
We currently have one wall which is effected by damp on the inside. Two builders that have looked at it think its probably due to the cavity wall insulation, so I have been searching that online.
I have read about CIGA, but we have no paperwork on the CWI due to it already being in the house when we purchased it. Can I contact the CIGA to find out if we are still under warranty? Also does anyone know their contact details? Thank you.
Hi Lisa,
I am not sure to be honest – I would give them a call and see what they say.
The contact details are as follows:
The Cavity Insulation Guarantee Agency
CIGA House,
3 Vimy Court, Vimy Road
Leighton Buzzard
Bedfordshire.
LU7 1FG
Contact Numbers:
Phone: 01525 853300
Fax: 01525 385926
Email: info@ciga.co.uk
Can you tell me how I find out who installed the cwi at 40 Balston road Poole Dorset as we brought the house in 2006 and have no paperwork thanks
Hi Peter,
With regards to WHO carried out the installation of CWI at 40 Balston Road, Poole, Dorset, we can run a CIGA Guarantee search for you. Please get in touch, if you require further assistance.
Regards
Southwest Insulation & Extractions Ltd
Hi
we are having problems with wet Rockwool insulation in our block of flats. Could you find out if we are covered by GIGA? The flats are at Haddon Court Queens Promenade Blackpool Lancashire Fy2 9BB
Many thanks
Could you tell me whether this issue has been resolved Jean? I have been looking at properties on Queens Prom and they all seem to have a simlar problem. Many thanks.
Hi we are buying 53 wardcliffe road ,weymouth dt4 0hp ,THE survey says the cavity wall insulation is causing the damp ,could you please run a CIGA quarantee search for me .Do you charge for doing this many thanks Mrs Moore
hi have a look in the loft space near your loft hatch they might be a card or paperwork saying who installed the cavitywall insulation
Hi Peter,
I am sorry we would have no idea how to do this! Apologies!
We had paper insulation put in the walls, but the walls are ice cold, it does not seem to have improved the warmth of the property. Would like it removed and straw insulation installed, but how much would this cost? The paper insulation has been in about 10 years, so is still under guarantee (but I think the paper insulation is rubbish).
My wife has become very allergic to formaldehyde. We discovered that we had urea formaldehyde foam in our cavity walls. I found a company that specialised in removing it. The boss of the company said that the foam would have started to degrade. However, when they came to remove it the foam was rock hard and they had a hell of a job to remove it. We had to seal up everywhere in the bungalow to stop the stuff coming in. It does go into the loft and they hovered that out to the best of their ability. We just has a formaldehyde test done in our property having already removed anything that could be giving off high levels. We had very low levels of VOCs and also very low levels of mould. However, the formaldehyde levels are elevated.at 54 ug/m3. My question is has the formaldehyde impregnated the walls?
90% sure im having problems on my gable wall due to cavity wall insulation . cold spots mould damp . looked a drilling pattern on external walls totally diffrent from instulation instructions for the tye of stuff thats been put in . if this is case surely its bad workmanship ? & will need fixed under guarantee
had cwi put in in 2008 a year later in the front bedroom above the window and to either side the wall and ceiling began to show signs of damp believing it was my roof i had different work done on it none of which solved the problem and finally a new roof fitted ( even though 4 different roofers said it was ‘ sound’) so far it has cost over 4 thousand pounds but the damp is back it was then suggested to me it could be the cwi. i have a surveyer coming out in a few days from the company who installed it but even over the phone he is insisting its not the cwi and if its not i have to pauy for his visit £50. i am a pensioner and now cannot aford to have it removed privately. it has honestly got me at my wits end .Now it sounds not such a rare problem. how do these firms justify themselves making peoples lives a mysery . do they think people enjoy being worried to death when they wont do the right thing.
Hi
my house was bought 3years ago without any paper work for CWI, but inspecting the property it obvious its been done. the house itself looses the heat so quickly,
conacted CIGA they had no record of the property, contacted a companys to check, but they where only willing to say what i already know that it has CWI, and it cost appromx 3000 to remove. I was hoping they be able to add to the inulation, unfortunate they needed to check the material used and it turn out that they was not able to mix the two. surely there must be a company that test the gase gives off by the material used.
if the walls were to be painted with water resistance paint would this be sufficent repellant for the rain in most case.
Hi
I had cavity wall insulation installed as it was advised by the goverment. After a few years I have had nothing but trouble , damp around the windows and doorways where for 40 years there was nothing and the exterier plaster has started to blow off in places which has left me with having to get the wall replastered which is not cheap. I have wrote off to the insurance firm which happens to be basesd out of the country and who never bother to reply as it may be a cost to them , the installation firm cant be found at least by me. It has turned out to be one nightmare for me. the material used is a sort of fluff.
to the first one I have found to write too
Mr P.Richards
Hi Peter, please send an email to mailbox@thegreenage.co.uk and we can help get this resolved if you would like our assistance. We have teams up and down the UK that can remove incorrectly installed cavity wall insulation.
I had UREA FORMALDEHYDE FOAM RESIN 29 years ago in July 1986. Spoke to the installer today (21-10-15) and it then met the British Standard Institute Certificate BS 5618 – cert No FS 252. He assured me it was there for life as I did not notice any on a small outside repair round a pipe outlet.
Can any more be pumped in? Does any one do a check to test it is still effectively there? Would a full house survey to a potential purchaser check its viability?
I spoke to James and Gary who were incredibly helpful in getting my damp cavity wall insulation removed. They took me through the entire process and although CIGA didn’t pay to remedy the work they put me in touch with a certified cavity wall extraction company. Thank you for all your help!
We had paper cavity wall insulation installed just under 10 years ago. I am concerned that this isn’t a great insulation material. Can I install a second insulation material without going to th expense of removing the existing?
Hi Phil,
The existing insulation will have to be removed if you want to insulate with something else. Unfortunately this is pretty expensive – if you get any damp at all it might be worth getting in an expert to take a look.
What would you do in a situation if you have had 1920s narrow cavities and a Government company filled it with the foam? Basically the reason I am saying this is that we have started to get damp in the property without having these issues before.
Insulating a house with a cavity, choosing not to insulate the cavity and adding external wall insulation!! You the authors are the Cowboys!! Know your facts before adding this rubbish to your site?,!
Under a Goverment scheme we had our home insulated we are not sure what was used but couple of months later we are experiencing damp in two of the ground floor rooms.we have tried to contact the firm who installed it but they have gone into liquidation.can you give us any advice on how to proceed .Thank you
Hi Anita, I think one of the team have been in touch – but I am afraid this is a common problem! Cavity wall companies are going into liquidation on a regular basis right now since there just isn’t the work to sustain them. The first port of call should always be to speak to CIGA – but people get very mixed results! Anyway, we can come and carry out surveys etc if you need so just give us a call if you would like!
Very useful service from Thegreenage. They helped us through the whole process (CIGA etc). In the end it did have to be removed to stop the damp coming through but even the cavity wall insulation removal was done with a minimum of fuss. Would really recommend.
Thanks Piersey1972 – we are finding more and more people are looking to have cavity wall insulation extracted – but as it is a relatively new process, there are lots of companies starting up to jump on the bandwagon and some don’t follow the correct procedure (some obviously do!). The first port of call is always CIGA to cheque if there is a guarantee in place for the works carried out on your home. If so then they can force the company to remove it if the company is still in business. Just be aware though that many cavity wall insulation companies are now going bust since the number of cavity walls that are still able to be filled are obviously dropping dramatically which means that the CIGA guarantee might not really help!
Hi im just wondering how the formaldehyde is removed , what methods are involved and how is desposed of please, i have a property that needs extracting and could do with this information .. Many thanks
Hi Leigh, take a look at Extraction4Homes!
We have had a survey on our house and been told by the surveyor we have damp and thinks it’s down to the cavity wall insulation . Anyone any idea how I go about having it removed and what it’s going to cost
Hi Anne, cavity wall insulation removal is the biggest area of growth in this industry! Cavity wall insulation does work well in about 99% of cases, but in some homes it just isn’t possible. We work with these guys – Extraction4homes, who carry out a very proffesional service, but there are certainly other companies also offering a removal service. You are looking at approximately £20 – £25 per m2 to get the cavity wall insulation removed.
Hi ann,
Will remove your failed insulation. All pictures are date and time stamped and they will help you with putting a claim in so you receive your money back.
My property is pretty damp and I thibk it had cavity wall insulation two years ago. How much would it cost to remove and can you recommend any local installers?
Hi Yves, where abouts are you located, we have partner organsiations that specialise in cavity wall insulation extraction all over the country.
The price depends on a couple of things – 1. the type of insulation injected into the cavity in the first place. 2. The area of cavity wall that needs the insulation extracted, obviously for the extraction company, the bigger the better and this tends to allow them to be more competitive.
As a guide though you are looking at prices starting from approximately £18/m2 for cavity wall insulation removal.
Hi Alan, I have just moved into a property that has cavity wall insulation and I have heard lots of horror stories about the insulation leading to damp. As a result I want to get the cavity wall insulation removed asap. Can all types of insulation be removed or is it only certain types and is there a UK wide database that exists that has the type of insulation I have? I don’t want to pay for a survey only to be told mine can’t be removed.
We are trying to sell out property. It is timber frame and when the buyer had their survey it was picked up the cavity had been insulated. Is this a relatively simple process to remove the cavity wall insulation in this case? Do the cavity wall extraction companies provide a certificate that will be accepted by mortgage companies proving the cavity is now empty since I guess that is what we are going to need.
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When we had double glazing fitted it was noted that the cavity fill beads had not reached several areas due to narrow cavities in some places. The beads also escape if holes are drilled in the wall or from the top of the cavity in the loft if it is windy. If we had the fill removed would we be eligible for a grant towards new modern, efficient fill? Could one company do both processes at the same time?
hi adding a bathroom event into gabel wall resulted in loss of bead insulation to create a void at top. Is this ok to be left well alone as ciga still not got back to us about wheter we need to get refilled or not. Also adding asubfloor airbrick elsewhere resulted in more oss of beads and on checking no beads could be seen to the area above so an lunlined airbrick was placed in situ to subfloor Is this likely to create problemsif rest of that wall is insulated with beads still
I had a damp area above one window in my house. The cavity walls had Rockwool installed by the previous owner some 25 plus years ago.
The cause of the damp was the breakdown of the cement used to fill in the instillation holes which let water into the cavity. Once cleaned out and re cemented the damp stopped!