Cavity Wall Insulation Problems

Please read before you have Cavity Wall Insulation Problems, and need your Cavity Wall Insulation Removed. The cost for fixing damp, mould and condensation issues which are left behind from the insulation installers is expensive. It may well be free, and funded by grants for the install, but there is no funding to extract the insulation.

The Insulation industry has gone full swing since last years storms, with the maker of the insulation blowing machines now making machines to remove the insulation! To find out more about how it’s done visit Extract Insulation Ltd.

The cavity wall construction is the modern method for house building, consisting of a block/brick inner leaf and brick on the outside, which has a cavity, usually between 50-100mm in width. The cavity wall was first used in coastal locations to keep out the rain but soon spread to other drier locations, as it was identified that the cavity also provided a degree of thermal retention. A cavity is essential in preventing water penetration, as the single 1 brick thick external wall will always allow water through when exposed to the wind driven rain, due to the drying process as the mortar shrinks at the perp vertical joints. Cavity walls were built to ensure there is that there is an air gap, this allows water to penetrate and run down the inside face of the brick to the foundations. However, if cavity’s are filled, this allows a direct path for water to penetrate, and can lead to dampness showing on internal finishes.

Buildings built with galvanised fish tail or wrought iron wall ties may have problems, as the damp conditions within the injected cavity can lead to corrosion and subsequent wall tie failure, which can be costly to remediate.

Extract Insulation Ltd conclusion is there is undoubtable problems caused by injecting retro – fitting insulation into wall cavities which can lead to cavity wall insulation problems, which may far outweigh any thermal retention benefits.

Cavity wall insulation will also alter the performance of traditional buildings, and can exacerbate existing moisture-related problems or create new ones. Any application of insulation requires caution particularly where walls may be damp. Its a good idea to have humidity tracking extraction fan fitted in bathroom and kitchen to ventilate theses area, you can buy these at are shop.


The available techniques for insulating existing cavity walls generally involve injecting or blowing an insulating material into the cavity. This works by entrapping and combining with the air in the cavity. There are three generic types of cavity wall insulation that can be injected or blown into the cavity:

Mineral wool (Rockwool, Whitewool, Walltherm)

There are many different cavity fill insulation types, however the most widespread is blown mineral wool fibre, which is not water resistant, being able to hold 2 ½ times volume of water than its own weight, and can lead to damp patches and mould growth. In addition, when mineral wool fibre becomes wet, it can act to draw heat from inside a building, increasing your fuel bills. The insulation may also have voids / gaps which can directly cause or lead to condensation problems, and as it is difficult to inspect the cavity, this can often go unnoticed and be hard to detect. Insulation can also sink under its
own weight, and or insufficient insulation material may be injected, which in turn create the ideal conditions for mould and condensation growth, as this leads to cold spots, and thermal bridging to occur at high level.

Beads or granules

Bonded Polystyrene beads have been known to less likely to transmit water across the cavity, as the beads themselves are waterproof, they have been known to leave no voids, this is why if you did choose to insulate the cavity walls, this is the one I would recommend.

Urea-Formaldehyde Foam

Urea-Formaldehyde Foam insulation is also subject to problems as it needs to be ready mixed on site and so is prone to human error, and generally brakes down over a period of time causing voids in the cavity. If the mix is too strong, it can cause pressure on the walls, leading to cracks bridging above DPC level and causing further wall damage. When removing/extracting Urea-Formaldehyde Foam insulation the problem comes as Extract Insulation needs to use compressed air with a directional nozzle to force the insulation towards an industrial hoover. Also a whipper (a rubber hollow tube that air comes out) is used, this spins around in the cavity like a Catherine wheel effect breaking down the remaining cavity wall insulation, thus can cause foam dust particle to enter the roof space and the property that the insulation is being removed from.


The cavities need to be above 50mm in width for most cavity wall insulation to be installed. Apart from Bead, Foam and certain types of fibre i.e Knauf Carbon Plus which can be installed in cavities 40mm and above.

Before deciding to fill an early cavity, check the cavity size and establish whether there is any material within the cavity itself.

The products that are available for cavity wall insulation are not in themselves very high performance insulators, particularly if the cavity is narrow. For this reason it is not normally cost effective to install insulation in cavities of less than 50mm width. In addition with such narrow cavities there is an increased danger of the insulation itself allowing water to cross the cavity to the inner-leaf.

However, cavity wall insulation in suitable situations can be a highly cost effective measure although there are certain technical risks in using this method to insulate an early cavity wall. The suitability depends mainly on the local exposure to driving rain and the condition of the existing construction. As many early cavity walls were built in areas with severe exposure to driving rain this makes many of them particularly susceptible to damp bridging the cavity through the insulation even at widths greater than 50mm.

The condition of the existing wall is critical to the cavity wall insulation process as any cracking to the wall needs investigation. If the cracks are due to wall tie corrosion it must be remedied first as cavity wall insulation will only make the situation worse. Cavity walls with widespread spalling to the face-work should not be filled.Call us on 02393 880032 All mortar joints should be full and the pointing in good repair.

Cavity wall insulation must always be carried out by a certified installer who is required to carry out a thorough survey of the cavity with a boroscope (in accordance with BS8208) prior to the work being carried out. The purpose of this survey is to check the cavity meets the stringent requirements of the required standards. There are a wide range of potential problems due to not having a proper survey at the start! In my experience most surveyors are more of a salesman the want your signature for their commission. They should be looking at all aspects of your property for example damp problems, exposure to wind driven rain, condition of the outside fabric of the building to name a few.

Filling the cavity with insulation introduces the risk that moisture will be able to find its way across to the inside leaf, whatever the insulation material used. There is also the possibility that the installation will be less than perfect, leaving unfilled air pockets creating cold bridging to the inside walls which may attract condensation.

If you are having Cavity wall insulation problems with damp and mould – Email:

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