Damp caused by cavity wall insulation.

The following post is a short review of the current situation regarding dampness caused by cavity wall insulation. However, what we need to address are the facts, which seem to be in short supply regarding this subject. Have you seen any damp caused by cavity wall insulation? I asked myself this when I read some of the recent media posts, particularly Jeff Howell’s piece on damp caused by cavity wall insulation^.

Below I explain why there is a need for more investigation on the real causes of damp in buildings and what role retro-fit cavity wall insulation has.

Almost all cavity wall insulation installations show some variation in density – is this always going to cause a problem?

The facts are that cavity wall insulation has been installed in millions of homes and the number of complaints is quite small. This would normally indicate that problems are rare. However, as described on many web sites and in Jeff’s post, some damp problems may be misdiagnosed, so that the cause is described as due to rising damp, penetrating damp or condensation, even if cavity wall insulation is involved.

Of course we must remember what cavities are for. They are not related to insulation and are there to reduce the chance of rainwater penetration across a cavity to the inner leaf of masonry, where it can cause damp. Filling the cavity will always present the ‘possibility’ of bridging. However, modern hydrophobic materials do not attract water so in theory, penetrating damp shouldn’t be a problem.

Some say that the cavity supplies vital ventilation and that blocking this free flow of air may also cause damp. However, the vapour permeability of most modern insulation materials is very high. Certainly much much higher than say, the internal plaster covering the walls or even the decoration, so once more, this shouldn’t cause issues.

So, what is going on and why are people finding damp, to such a severe degree that the insulation, when exposed, is wet through? Why is mould becoming an issue in some cavity wall insulated houses and is the CWI to blame?

Let’s imagine we have a well built pre-war house with a cavity wall. It is in good condition and a year or so after cavity wall insulation is installed the owner complains of a damp smell, a cold house and high energy-bills. He is a Telegraph reader and sees a post by a ‘claims specialist’ and asks for the insulation to be checked.

The cavity wall insulation removal specialist

Along comes the recommended cavity wall insulation removal specialist and, after a few checks he condemns the insulation as incorrectly installed and – it is responsible for all of the owners damp problems. These defects could include, some debris in the cavity, which was there before the insulation was installed. It could be that an air brick or two were blocked by insulation, there are voids in it or it could be that the house is near a westerly coast, or has a poorly pointed wall or some missing pointing.

Where the insulation is installed correctly – this is what should be seen in the cavity – no voids

This void turns out to be quite extensive

It’s true that where there’s a claim there’s a gain and this applies where cavity wall insulation is concerned

In many cases the insulation is removed, the debris removed and the walls are pointed and in some cases treated with a water repellent too.

This is brilliant for the claims company and his installers. It’s a disaster for the insulation company though (well, their insurers really).

Why should we care? Well the thing is that I see houses with and without cavity wall insulation, which are mouldy and damp. I’d be fascinated to see data on the environmental changes, which follow removal of insulation for comparison with data obtained prior to the event. Whilst I accept that there are many cases of poor specification and poor installation of cavity wall insulation, I just don’t see the evidence for massive effects on dwellings, apart from exceptional cases. Certainly nowhere near the touted 3 million homes affected, which some journalists are promoting as a probability.

Let’s not forget that the claims specialists have a direct conflict of interest here. They make money from the entire claims procedure; the inspection, complaint handling and subsequent removal of the CWI. In some cases they also offer the repairs, which ought to have been done beforehand, such as the pointing, cavity cleaning and such. I’ve no objection to this and have even explored the possibility of my own company carrying out CWI extraction, where I can see a need (very rare so far, other than isolated areas – see below). However, the conflict of interest is important, because of course it naturally colours the context of the discussions. There are now web sites galore telling homeowners that their insulation is a threat to them and is probably causing the damp… and of course that it can all be solved with a simple phone call to ‘our partners’ – this is called marketing and we all do it. It should be recognised as such – even if the web sites look like consumer information sites, which they are not, rather than adverts for services, which they are.

This insulation is causing damp and the remedy is to remove the insulation which is blocking the vent – not all of it.

We need to be adult about this avalanche of negative information about CWI. I haven’t seen much damp caused by cavity wall insulation. As a specialist damp surveyor that puzzles me. The media would say that this is because, as a damp specialist I am missing the symptoms. However, I can’t see that, given how careful, well trained, experienced and well equipped I, and many of my fellow Property Care Association members are. There are problems with CWI and I am not denying that – it’s the degree I am worried about.

Investigating the potential for damp caused by cavity wall insulation.

This issue needs investigating and ideally we need to follow through some of the CWI removal cases, to make sure that the cart isn’t leading the horse, so to speak.

A good way forward would be to find a few houses where the insulation is suspected as causal in the owner’s damp problems. A detailed survey should be done, separately from any claim malarkey. Data must form part of this, including at least a few weeks of data, recording the internal and external environment: vapour pressure differentials; surface temperatures and relative humidity.  A detailed moisture audit, to check for other moisture sources – the means of ventilation, heating regime and occupancy levels. All these are crucial because without this information, all we have is a cavity wall insulated house ,where the installer broke the rules – rather than a house where the insulation caused the problem.

I know the cavity wall insulation is not installed correctly – but is this ventilation duct involved in the damp problem at all?

In a perfect situation the data loggers would be left in-situ for a few weeks well after the CWI is removed and ideally other environmental improvements should be left alone – no improvements to ventilation or heating and such. Then a clear idea of the role of the insulation itself can be arrived at. An alternative would be to leave the CWI in-situ and address only the defects found. Improve the ventilation if that is poor, remove blockages from the cavity or unblock the vents.  Merely replace the local areas of insulation where voids are found. Perhaps apply a water repellent cream such as StormDry to the external walls if required. If that solves the problem, without removing the CWI, then that too would give valuable insights into what is really going on. It could also save CO2 as we are left with a dry insulated house, rather than a dry but cold house.

The house is on the cold side and the electric is expensive – but this is a water vapour machine.

The rules about insulation installation are clear and they’ve been broken many times. The insulation industry must be feeling pretty worried about developments. However, are these incorrectly installed jobs really causing as much damage as we’ve heard? The truth is that nobody really knows. We know about the really bad cases of bad practice in installation, but we now have a new industry emerging, paid for by the claims system. Is it right that this industry should form opinion, without independent research on the subject? In addition, what role does subsequent work, done after cavity wall insulation has been installed, play in all this? I have written quite a lot about the possibility of wall tie installations causing damp problems in houses with CWI installed. We’ve all seen how much debris can be pushed into a cavity by a tradesman installing a new soil and vent pipe or a boiler flue too.

I intend to have a chat with some of my peer group in the damp diagnosis industry and we may be able to get some data to address the lack of information. If you have a house which is damp and the insulation is being blamed and you live in Yorkshire, I’d love to come and have a look…. please get in touch.

Dry Rot.

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