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.
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.