Cavity walls were designed to prevent the ingress of water however penetrating damp can still occur. A bridge across the cavity can be formed, which allows rainwater to move through to the inner surface of the property. This occurs for example where;
- the cavities have been incorrectly filled
- the wall ties have been incorrectly installed
- obstructions exist in the cavities
- the insulation was not properly installed
What are cavity walls & how do they work?
Cavity walls were originally designed to be used only in coastal areas of Britain and Ireland to prevent wind driven rain from penetrating to the inside of homes. Cavity walls soon became the preferred practice in construction across the country and now over two-thirds of dwellings in England (70%) have them.
Cavity walls consist of two walls known as 'skins' separated by a hollow space, the cavity. In driving rain the outside cavity wall becomes saturated and water (often in quite large quantities) runs freely down the inside cavity and escapes at the bottom through weep holes. This process prevents water penetrating to the inside wall. The weep holes also allow air to flow and remove evaporated water from the cavity.
Does cavity wall insulation cause damp?
Research shows that cavity wall insulation (CWI) can cause damp but it depends when, where and how it was installed.
From the 1980's onwards, the Building Regulations have required all new houses to be built with insulation material in the cavity. In most cases, the insulation material (normally in the form of rigid foam boards) are fixed to the inner wall leaving a small gap in the cavity to allow any rainwater to run down. If the insulation is properly installed during the construction phase then it should not hinder the cavity wall from protecting against rain penetration.
When retrofitted, however, through the process of injecting an insulating material (such as fibres, beads or a foam) into the cavity, cavity wall insulation has the potential to cause damp. The Building Research Establishment (BRE), a world leading, scientific research centre published their BRE Good Building Guide (44, Part 2) which provided the following guidance on cavity wall insulation;
“There can be an increased risk of rain penetration if a cavity is fully filled with insulation, i.e. moisture is able to transfer from the outer to the inner leaves resulting in areas of dampness on internal finishes. Rainwater, under certain driving rain conditions, can penetrate the outer leaf of masonry leading to wetting of the cavity insulation, a reduced thermal performance and damage to internal finishes.”
How can cavity wall insulation cause damp?
There are a number of possible ways cavity wall insulation can cause damp, this article will focus on the following two ways;
- Wind driven rain
- Poorly fitted insulation
Wind driven rain
By filling a cavity wall with insulation, you can end up removing the space necessary for water to freely escape the building - the wall can then no longer function properly to protect the building from damp.
When the building is exposed to wind driven rain, the outer wall becomes saturated with water, the insulation then acts a bridge for this water to reach the inner wall and cause damp.
Such is the potential for wind driven rain to penetrate cavity wall insulated walls that guidance exists to suggest some homes in the UK are simply not suitable for this type of retrofitted insulation.
Despite a significant increase since 1996 in the prevalence of cavity wall insulation across the UK, the geographical location of your home and the amount of wind driven rain it is exposed are very important factors when it comes to the risk of damp. The Government’s Energy Saving Trust website states that homes are only suitable for cavity insulation if the walls are not exposed to driving rain.
The BRE Guide divided the UK into levels of exposure zones which indicate the approximate amount of wind driven rain which a building may be subject to. The image below, featured in a Which? article, displays these exposure zones.
According to the BRE Guide, homes in Zones 3 and 4 which include Wales, West Scotland, Cornwall, Somerset, Devon and the North West Coast are not suitable for cavity wall insulation due to high levels of wind driven rain.
Additionally any assessment into the property's suitability for cavity wall insulation also needs to take into account the local features and geographical terrain which may make a building more or less suitable for this type of insulation and the risk posed from wind driven rain.
Poorly fitted insulation
Proper installation of cavity wall insulation, which follows the industry's best practices, is essential for the long term performance of the insulation and the avoidance of damp.
Unfortunately some companies do not always follow the rule book and the property owner has to deal with the resulting long term problems. Examples of poor company practices include;
- Failure to perform a thorough survey to assess the property's suitability for cavity wall insulation
- Ignoring factors which would deem cavity wall insulation unsuitable and installing it regardless
- Failure to address and remedy existing building defects and obstructions in the cavity
- Insufficient amounts of cavity wall insulation used
- Uneven installation - leaving voids
The cavity itself should be thoroughly inspected prior to installation to ensure the wall meets strict British Standards. Unfortunately a lot of cavity walls have unfilled mortar joints, debris and wall ties covered with mortar droppings These obstructions can not only act like a bridge for water to pass through to the internal wall but they can also prevent the insulation from filling the cavity evenly. Gaps in the insulation can lead to temperature variations and 'cold spots' on the internal walls - when warm air touches these 'cold spots' it can result in condensation and mould.
Voids in the insulation and the ensuing problems with 'cold spots' can also occur over time due to an insufficient amount of insulation material being installed in the cavity wall. As time passes, the insulation can sink to the bottom of the cavity leaving 'cold spots' at the top of the wall.
It is also essential that the cavity wall ties (cavity wall ties join the two leaves of a cavity wall together and provide structural stability) are inspected prior to the installation of insulation to ensure there is a sufficient number of them and that there is no evidence of corrosion. It is much more difficult and problematic for the homeowner to fix any issues with the wall ties once cavity wall insulation has been installed.
It is also important to remember that buildings need to "breathe" and they rely on constant air circulation. In cases of poor cavity wall installation, essential air vents have been blocked with insulation which consequently impedes the flow of air through the home. If moisture is unable to escape or evaporate this can also lead to damp problems.
What problems can damp cause?
Damp can cause a host of problems not only for your home but for your health and your pocket too! It is therefore essential to address any signs of damp as soon as possible.
Protect your health
Damp creates an indoor environment that is detrimental to your health. The World Health Organisation consider excessive dampness and mould a "threat to health".
Damp becomes a breeding ground for fungi, bacteria and mould which subsequently emit spores, cells and volatile organic compounds into your home.
"[I}f you have damp and mould you're more likely to have respiratory problems, respiratory infections, allergies or asthma. Damp and mould can also affect the immune system."
Protect your home
Damp can not only cause damage to the decorative finishings, ruining paint and wallpaper, it can also cause structural problems.
If the cavity wall insulation is damp it can accelerate the rusting of the wall ties, causing them to corrode much quicker. Failure to rectify these issues can, in extreme cases, lead to the external wall collapsing.
Protect your wallet
If the cavity wall insulation becomes saturated with water, it will reduce the thermal performance of the material. Damp insulation materials act as a thermal bridge (sometimes referred to as a cold bridge or a thermal bypass) causing heat to transfer away from the building. Damp cavity wall insulation can potentially increase heat loss (and therefore increase energy consumption) rather than reduce it.
What can be done about damp caused by cavity wall insulation?
If you believe your home is being affected by damp caused by cavity wall insulation there are a number of things you can do to take action to protect your home, health and your wallet.
- Contact the company who installed the cavity wall insulation and ask them to inspect the damp and what they can do to resolve it
- If you or the previous owner were given a 25 year guarantee for the cavity wall insulation, you can contact the Cavity Insulation Guarantee Agency (CIGA)
- Rectify any building defects which could be affecting the cavity wall insulation and contributing to the damp
- Remove the cavity wall insulation
If your home is exposed to a lot of wind driven rain, there is another way to protect your home from damp. Apply one of our highly water repellent coatings and keep your walls dry, whilst still allowing them to breathe.
How can a wall coating help with damp?
Wind driven rain causes the outer wall to become saturated with water and as discussed above, the insulation can then act as a bridge for this water to reach the inner wall and cause damp. However, if you apply one of our highly water repellent and highly breathable coatings, you can keep the outer walls dry and thereby prevent water from moving through the cavity to the inner surface.
Surfaces treated with ProPERLA super hydrophobic coatings reduce water absorption by more than 95%. When it rains, the rain water forms beads and simply rolls off the treated surface leaving it dry, very similar to the super hydrophobic capabilites of the lotus leaf.
To be considered super hydrophobic, a coating needs to create a high water contact angle- most water repellent coatings create a contact angle of only 40-50 degrees, ProPERLA creates an angle of 140 degrees.
It's important to note that ProPERLA is not a sealant- it does not trap moisture or impede water vapour from escaping from inside the building and evaporating naturally.
The video demonstrates the ease in which air (trapped in bubbles in this case) is able to permeate and escape a masonry block treated with ProPERLA Facade Coating.
ProPERLA Facade Coating benefits from an SD rating (breathability rating) of 0.06 whilst ProPERLA Masonry Creme has an SD rating of 0.03 - these are both much lower ratings (and therefore more breathable) than an SD rating of 0.5 which is considered breathable by industry standards.
Keeping walls dry not only helps to protect against damp it also helps you to reduce heat loss and contributes to lower energy bills.
ProPERLA uses the latest silicone resin based nanotechnology to create coatings that can give you long term peace of mind- they come with a manufacturer's guarantee of between 10-20 years.
ProPERLA is suitable for a range of substrates and with the option to maintain the natural appearance of the walls or select a coloured finish, there's a ProPERLA coating for everyone.
Call 0161 763 7074 to speak to one of our technical advisers for further advice on our range of ProPERLA coatings and how they can help with damp.