How does external wall insulation prevent damp/condensation in the home?

Properties suffer from damp for a number of reasons, some more obvious than others. Three common examples are penetrating damp ( e.g. due to driving rain or blocked guttering), rising damp and condensation.

In this article, we will explain how damp is caused and how external wall insulation may help solve the problem.

Damp caused by condensation

Walls that do not get enough heat or solar radiance may suffer from condensation. A lack of air flow in rooms is also a common cause of condensation, as the water vapour which has built up is not able to escape. When the outside walls are remarkably colder compared to the inside, this can exacerbate the problem even more. When these two forces meet this causes the water in the air to be condensed to a liquid, causing condensation. Sometimes if the room is well heated and ventilated, most of the build-up will disappear by itself. But if not, condensation can become a regular occurrence.

So what is the solution for this form of damp?

EWI is a great way of getting rid of condensation in your home. The way it does this is by creating a tea cosy effect, altering the way the inside of the home works. The cold walls which were causing a lot of the problem will not be cold walls anymore, as the insulation will protect the bricks and keep them warm, meaning the difference between the temperature of the inside and the outside won’t be as extreme. The rooms of the home will also retain more thermal mass as the heating is stored in the fabric of the walls and released back into the room when the heating is turned down. As a result the heating system will work more efficiently.

Note: the likelihood of condensation is now much lower, but the amount of water vapour inside the property (caused by us, breathing, washing, cooking, drying clothes etc.) is the same. Excess water vapour is mostly dealt with by a proper ventilation system, but that’s another story…


Damp caused by penetrating water

If the property has problems with guttering and downpipes, water will find its way into the walls – damaging the brick work and over time potentially causing water to penetrate the property.

External wall insulation itself will not fix broken gutters and downpipes; all this has to come off the walls for wall insulation anyway for the walls to be insulated, so you will have brand new ones. If, however, the walls are stained by water damage, the EWI will cover these imperfections as it will be covered by a much more aesthetically pleasing layer of render.


Rising damp issues

Rising damp is where the moisture travels up from the soil into the dry brick work, causing wet patches from the ground up. This can happen if there are cracks in the damp-proof course (DPC) Rising damp will become noticeable on the outside of the property as well as the inside sometimes.

If you have this problem, it is advisable to insert a retrofitted DPC before you attempt to insulate externally. Once this has been done, the best solution is to use an insulant with hygroscopic qualities, such as wood fibre or calcium silicate.  This will wick out residual moisture in the masonry over time.


So does EWI prevent damp?

To conclude, external wall insulation is a good preventative measure for condensation and damp ruining the property. If you have guttering problems or rising damp, these can be repaired before or during the installation.  External wall insulation will keep your home warmer and cosier, and providing all other potential issues have been addressed, keep it free from damp.


Written by Leanne Groves.