When the government is gaga over cavity wall insulation, it’s natural for every home owner to contemplate over opting
for CWI. As an expert in cavity wall insulation, I can only say that it’s completely your decision to go on with cavity wall insulation but first read down the facts I have mentioned below.

Based on my prolonged professional camaraderie with Cavity insulation, I will point out the typical pros & cons of opting for Cavity wall insulation.

Let’s start with the pros

Well, the obvious advantage of CWI is prevention of heat loss. It implies that your house will stay warmer in extreme cold if you can successfully and appropriately insulate the cavity walls. Another very important factor here is that you will experience reduced heating bills. In fact, Retro fitted cavity insulation is advised by the government as a measure to address the staggering energy costs.

Another important benefit of CWI is that effective insulation helps to lower the carbon footprint by a great extent.

Next, the government has announced to offer CWI completely free of cost to every homeowner here, over 70 and people on certain benefits.

Then, CWI installation is a fast process and gets done within just a few hours in most of the cases. In a rare case, it might take a days to insulate your entire home.

Moreover, you can expect a prompt response from cavity wall insulation. Your home will get warmer since the first day of the installation and you will experience high energy savings immediately.

The cons

The most prominent con of cavity wall insulation is the damp trouble and the main culprit here is the insulation material itself most of the times especially mineral-wool fibre. Although the material is largely claimed to be water repellant but, on the contrary, it does not carry any waterproof benefit & only absorbs water leading to high moisture & damp. Then, another material, bonded polystyrene bead undesirably can transmit rain-water across cavities which consequently leaves you with a damp house. Basically, in a lot of cases, poor installation of polystyrene beads result in insufficient bonding which permits beads to actually “escape” leaving voids behind. Now, when these voids get filled with rainwater, these tend to channelize the water across cavity instead of dripping it straight down, as required.

However, what I have found that the damp issue with CWI is mostly prevalent in homes located in high wind-driven rain zones.

Besides, one of my recent projects last month showed that gaps in insulation too can create voids in the cavity walls. These voids further experience condensation, which automatically accelerate dampness in the home.

thermal insulation survey

Does Cavity Wall Insulation Cause Damp?


Cavity Wall Insulation has been promoted widely by the government to address heightened energy costs. Building Regulations, since 1980s, have made it essential for all new constructions to be structured with cavity wall insulation material. Now, if the cavity wall construction has been built properly, the insulation won’t compromise walls’ opposition to rainwater penetration.

Damp occurs

But, my experience in the industry has shown that CWI is prone to damp issues, especially if the home is in a high wind-driven rain zone. BRE has forwarded that the single-leaf brick cavity walls tend to leak always while exposed to severe wind-driven rain, which in turn further leads to dampness in the house. The leakage takes place at vertical joints in between the adjacent bricks given drying mortar shrinkage.

It should be noted here that the CWI leakage & damp issues are mostly common in older homes (built before 1980s) where clear cavities were filled with insulation (retro fill).

Insulation materials causing damp

The damp factor in CWI is largely dependent on the insulation materials used. The material that we found to be particularly troublesome is mineral-wool fibre. According to its manufacturers & installers, this is a water-repellent material which doesn’t allow the rainwater penetration across cavity. But if you want my honest and expert opinion, this claim is a myth and the very material actually absorbs water just like a blotting paper. This in turn, results in high moisture formation and inevitably dampness in your house.

Another important insulation material here is bonded polystyrene bead which we have found to channelize rainwater across the cavities, leading to damp. Now, unlike mineral-wool, this one is actually waterproof. But, if cavity filling stays incomplete, there would be voids that would be filled with rainwater & based on their configuration; the voids might straightaway transmit the water across cavity. In most of our CWI removal projects, we have found that in a lot of cases, CWI with the polystyrene beads had resulted in insufficient bonding which permits beads to actually “escape” leaving voids behind.

The other insulation material that has caused damp issues is foam.

To find out more on how we remove cavity wall insulation , a case study on a foam extraction or simply to find out the cost of a extraction

Gaps in insulation

One of our latest projects in south east England shows us that when it comes to CWI damp issues, the problem might be a result of increased condensation as well. It’s not always the rainwater transmission across cavity which is the culprit here. My research around has proved that around 40% of homes with mineral-wool fibre CWI are suffering from insulation gaps. These voids result in condensation and ultimately dampness & the consequent peril of black mould in the houses.

Can Cavity Wall Insulation Be Removed Or Extracted?

Though CWI with insulation material is increasingly advertised by the government as something must-have for every home here yet in reality, the boon has turned out to be a bane for many. The most prominent problem here is the damp issue from ineffective CWI that has led to harmful black mould and deteriorating property for many. Now, as a CWI expert, I tend to receive calls & emails from homeowners asking whether their CWI can be extracted or removed to address the damp issues.

Well, I am a seasoned cavity wall insulation remover and my answer is ‘yes”. If you need, we will arrive at your house and extract or remove the cavity wall insulation for you. We have successfully helped a lot of clients across England & Wales for years now to get rid of the cavity wall insulation and the related ugly dampness.

We deploy a specialized insulation machine to pull out the insulation material as well as the dampness from your cavity wall. The most notorious insulation material that must be removed if you are suffering from severe CWI damp problem is mineral-wool fibre which tends to absorb rainwater leading to damps in the cavity wall. Ironically, the material is advertised as water resistant which is far from the truth. The other insulation materials that act as culprit here are urea formaldehyde and bonded polystyrene beads. Our high quality equipment’s can successfully extract all these insulation materials if you are suffering from damp issues due to faulty CWI.

Typically, we start by drilling through holes which were actually used for the installation of insulation material in your cavity walls. Our high-pressure hoses & vacuum sucks out insulation from your cavity wall to remove the older insulation from your home. The process might take 1-2 days for a typical home. In some case, we had to replace the brick or offer a touch up if the wall is too messy post the removal or extraction of the insulation material.

If you are looking to know whether or not you should be re-installing the insulation. Once again, I will advise that “don’t”, you might end up with the damp issue once again.

Do you want to know more about cavity insulation removal & replacement?

We also receive mails from troubled home owners who are looking to know about the cost of CWI removal or extraction. The cost obviously varies from one project to another, depending on the size and need of the house. I am providing a very rough and basic idea on the cost.

Well, our service for a semi detached 3-bed property would be something like 1,800 – £2,500 while it would be £1,000 – £1,500 for one three-bed bungalow.

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