A blog post

Cavity Wall Insulation – what are the benefits?

Posted on the 28 August, 2009 at 2:54 pm Written by in Case Studies, Cavity Walls, Damp

Cavity Wall Insulation
(What are the benefits? …..…..DAMP)

From October 2008 all domestic buildings (being built, rented or sold) were required ‘by Law’ to have an Energy Performance Certificate (EPC) to help improve the energy efficiency of the building. The EPC provides an ‘A’ to ‘G’ rating for the building, ‘A’ being the most efficient and ‘G’ the least and to-date a ‘D’ rating is currently being banded as the average.

It is claimed that around a third of heat loss in a house is through its roof and walls and currently there is a government drive (supported by television advertising and the offer of Home Improvement Insulation Grants) to encourage home owners to increase loft insulation and also to fit cavity wall insulation, as it is claimed this can save on average around £180 per annum on heating costs!

However were you aware that by installing cavity wall insulation, whilst you may well be saving some money on fuel costs, you could also be creating a major expense for the future……..damp!

Example of cavity wall insulation

Example of cavity wall insulation

The cavity wall (as we know it) dates back to the early 1900’s and is commonly found in the coastal areas around Britain, used to reduce the risk of rain penetration. In the 1920’s, local building by-laws encouraged the construction of the cavity wall and by the 1940’s it had become the Industry Standard. The familiar cavity wall (as we know it) is two leaves of brickwork, forming a 60mm cavity and tied together with metal wall ties.

Even back in the good old 1970’s concerns were being expressed over Energy Conservation and home owners were then being encouraged to introduce loft insulation and it wasn’t long after that cavity wall insulation was also being recommended.

Fill your cavities with foam, polystyrene, mineral wool or any other material you can introduce through a small hole in the wall and you will save energy and loads of money. Sounds good, but what if by introducing this insulation you increased the risk of damp to your property, which in turn would cause internal decorative spoiling, plaster damage, fungal decay to  structural and joinery timbers and also accelerate the risk of corrosion to the metal wall ties.

Could that really happen? Well the answer is yes and it is.

Paul Carter, the principal of Premier Heritage, has investigated hundreds of buildings over the past 20 years of so, where damp has affected internal decorations etc and found that the damp present was due to bridging of the cavity by the earlier installed insulation materials. Whilst some of these cases were wrongly diagnosed by others as rising damp, most of these buildings (if not all) retained a physical damp proof course, the newest being a 1980’s brick built bungalow in Hampshire.

Ok, lets put this into perspective, there have been thousands of cavity built houses within the UK that have been insulated and a good majority of these don’t currently have nor will ever have a problem with damp. But there are a great number that have and no doubt more will be affected in the years to come! 

Increased rainfall in past years has resulted in a noticeable increase in damp problems affecting conventional cavity-constructed housing, due to moisture penetrating / bridging the cavities and in particular on the weather prevailing elevations and this isn’t a problem relating to current rainfall, but a gradual build of damp over many years.

Rainwater driving into the masonry of a building can penetrate the outer leaf brickwork leading to the wetting of the insulation materials, increased damp penetration and a reduced thermal performance of the material. Poor construction methods, mortar and perp joints, debris within the cavities, dirty wall ties and poor installation procedures by installers all contribute to the overall problem, which generally will result in the need to remove the insulation, which is not only expensive, but will almost certainly cosmetically scar the building when finished. Unfortunately it doesn’t come out through the same hole through which it went in!

So how do you avoid this problem? Well there’s no easy answer to this other than to look carefully at the building’s construction (porosity of building materials) and its exposure to the prevailing weather conditions. If having then decided to proceed, ensure that the chosen contractor / installer, during the survey, checks the cavities  and cavity trays for debris and dirty wall ties, but more importantly offers a system and material that guarantees (preferably insurance backed) that the materials being installed will not transmit / bridge moisture through and into the internal wall!

Alternatively, if you’re still unsure then don’t install.

Examples of Cavity Wall Insulation causing damp:

Cavity Foam Insulation

Cavity Foam Insulation

1970’s block constructed bugalow with poorly installed cavity foam insulation and debris bridging moisture via wall ties, cost around £800 to remove and rectify internal damage caused.

Polystyrene bead cavity insulation

Polystyrene bead cavity insulation

1930’s brick constructed house with polystyrene bead cavity wall insulation. Caused extensive damp to rear elevation walls, cost in excess of £3,000 to remove insulation and rectify internal damage.Polystyrene bead cavity insulation
Polystyrene bead cavity insulation

Polystyrene bead cavity insulation 2

1920’s brick constructed house, south facing elevation with polystyrene bead insulation and poor quality mortar. Caused extensive damp to internal decorations and accelerated corrosion of wall ties (rusting ends just visable), cost in excess of £3,500 to remove insulation and install new wall ties.

some comments

There are currently 102 of them
  1. Chris 30 December 2017 at 6:11 pm permalink

    Should add to above our house is only twenty years old and already has expanded polystyrene boards in cavity and they leave room for air circulation. Our house is lovely and dry inside and heating bills are very reasonable and I feel no need to risk structural problems and damp walls that may well result from CWI. I have seen a few neighbours houses insulated, the installers clambered all over their tiled garage roof without ladders and have probably broken some tiles.

  2. Bee man 20 August 2018 at 1:11 pm permalink

    As with all trades it’s only as good as the Tradesman that installs it!
    as has bee brought up many times in the comments the Mark Group didn’t care whether it as done properly or not as long as it was done and they got paid!
    should you have the cavity walls filled then firstly look at the longevity of the product used, Fibre is made with water repellent additives so that it prevents water entering the cavity, there are two serious issues with this, 1. the mandatory water permeability test for cavity wall insulation only lasts three weeks, what happens to these properties long term, well you only need to look at the huge number of damp houses that were installed 10 plus years ago! 2.As the density installed is often not calibrated properly on the day the majority of properties will have light filling, this can then slump leaving gaps or even have gaps left in the cavity on the day, either way this then creates a bridge that penetrating water can cross to the inner leaf and gaps lead to cold spots and condensation patches on the inner wall.
    so why haven’t these fibre materials been held in check? because the majority of the regulatory organisations funds come from the Fibre industry, why would they dent their profits.
    Foam insulation is expensive and while when installed correctly is great it again depends on the installers to correctly calibrate and fill the walls, incorrect ratios of hardener will lead to break down of the material over time.
    EPS bead is made in such as way that the density and thermal values are not reliant on the installer doing their job properly on the day, the material remains unchanged from manufacture so it is far more reliable, the other benefit being that it does not resist penetrating water into the cavity and will not hold water, therefore, for a bead material to pass the mandatory testing is much harder as it has no built in repellent agent, any water that passes through the brick into the cavity dissipates through the bead down to ground level without crossing the cavity, the same effect as filling the wall with marbles.
    the other main concern that must be addressed is the building suitability, if the cavity is poorly made with dirty wall ties, debris and rubble no matter what material is installed it will have issues with damp.
    the wall condition also matters, soft eroded mortar, lose render or damaged brick also have to be addresses before considering cavity wall insulation, the property should also me maintained over time to avoid any issues.
    another issue is condensation forming around windows and cold spots post installation, this shows that the insulation is working, the walls are now warmer so condensation doesn’t form across the surface, that warm moist air will move to condense on the cooler surfaces, ventilation is the key, cooking, drying clothes in the house etc will create warm moist air, this must be vented out to avoid the issue.
    ultimately, do your research and try to use a good stable installer that seem professional and undertake proper checks on the property ahead of doing the work.
    my house has already been insulated with Fibre but I think I am one of the lucky ones whos house was installed properly, if I were to have it done again, I would chose EPS bead.


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