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Why do properties actually suffer from damp?
Damp problems on a property are sometimes more obvious than others – for example penetrating damp due to poor or broken guttering, rising damp, and damp due to condensation. However, in our experience there are instances where damp issues also arise, but the actual cause may not be obvious to someone who does not come from a surveying background.
For this reason, if your property suffers from damp problems, we would recommend you consult a specialist who will be able to comment on the reasons behind this.
In the next section we introduce how damp can be caused in a property and the potential solution involving external wall insulation retrofit.
Damp caused by condensation (cold walls)
Walls that are either north facing, do not get enough solar radiance or are not heated properly in the winter months may suffer from condensation. A lack of air flow in rooms is also a common cause of condensation, as water vapour built up in a room is not able to escape the property.
This can become exacerbated when external walls are particularly cold compared to the inside air. When two forces meet against one another, this causes a “dew-point”, which condenses the water in the air to a liquid, thereby causing condensation. If the rooms are well heated and ventilated on the inside, it is possible for most of this build-up to dissipate away. But if not, then condensation could be a pretty common occurrence.
The first sign of this will be around the windows themselves. You will see them steam-up on the inside as the moisture has been allowed to “condense” on them. To be honest there may well be condensation present on the walls as well, but this may not be so obvious at the start of the process.
Persistent condensation will be more obvious when you begin to see water droplets staining the inside walls and eventually if untreated the condensation will turn to damp patches.
So what is the actual solution for this form of damp?
Insulating walls externally to prevent condensation
EWI is of course a great way to reduce condensation based damp!
Ensure the walls are nice and dry and free from any moisture when installing external wall insulation. The best time to carry out the works are between May and September when the weather tends to be stable and dry.
The external wall insulation will form a cosy blanket around your house, which will change how the inside of your home behaves.
The formerly cold walls will not be cold walls anymore because the insulation on the outside will keep the masonry bricks/ blocks warm, which will mean that there will not be a big difference between the temperature of the wall fabric and the air on the inside of the property – thereby mitigating the effects of condensation.
When the walls are insulated externally the rooms themselves retain more thermal mass as the heat is stored in the fabric of the walls and released back into the room when the heating is turned down. As a result, your heating system will work more efficiently.
Damp caused by penetrating water
As mentioned, if the property has problems with the guttering and downpipes water will finds its way onto the walls – damaging the brickwork and overtime potentially causing water to penetrate inside the property.
Where the property has leaking external fittings it demonstrates that it requires some repair work – not only to the guttering but potentially to all of the fascia boards and other parts of the roof.
Using external wall insulation to kick-off external property repairs
External wall insulation itself will not remediate broken gutters and worn out facia boards. All this has to come off the walls and put back on when the walls have been insulated. However, if the walls are stained due to water penetration, the external insulation will mask those imperfections as it will be covered by a fantastic layer of render.
If you have roofing issues, ensure this is fixed before you undertake the insulation. You may want to do this at the same time so that you can utilise the same scaffolding and not have to pay twice.
Issues with Rising Damp
Rising damp problems are really tricky to diagnose without having prior consultation from an external building surveyor. Essentially what happens is that moisture travels up from the soil into the dry brick work (bridging or going through cracks in the DPC), causing wet patches starting from the ground up. Evidence of rising damp will become quite noticeable both on the outer wall and potentially on the inside on the house.
External wall insulation is installed from the level of the DPC up to the soffit of the property. Most standard system designs do not cover insulation below the DPC. The EWI Pro system designers go into a bit more detail on how this could be treated.
First of all, bridging or the breakage of the DPC needs to be treated with a chemical or a Dryrod solution. This will make the existing fabric less permeable. Thereafter we recommend the DPC is insulated with the extruded polystyrene or XPS boards. The XPS boards don’t absorb water and will in addition provide an extra layer of protection for the base of the building.
Does external wall insulation prevent damp?
In summary, external wall insulation can prevent future damp on walls from condensation but it won’t mask existing problems of water penetration. If you have burst guttering, roof problems or rising damp, make sure you get those items repaired at the same time, or prior to the insulation being installed on the walls.
External wall insulation will keep your home nice and cosy and with all other elements addressed prior to application keep the property free from damp.
We have pretty poor render on the side wall and the water has started to soak in it. Would you recommend we have the insulation put on top?
Hi Magaret, ideally you would strip the existing render, wait while the wall drys out and then re-render the whole surface. If you are looking to benefit from the Energy savings then you would need to look into getting the insulation too.
I would knock all old render off and substrate the old brickwork then I would start insulation system
In a word Yes – EWI does stop damp! Stops penetrating damp and also helps prevent condensation forming on inside walls.
We had damp in our home and the render / insulation system has completely stopped it. The wall has dried out and in winter is much warmer to touch. I guess the render only would stop water entering the property, but the insulation increases the temperature of the thermal mass (e.g. the walls) and helps to prevent water vapour condensing on the surface.
We had our walls rendered a couple of years ago, and all was well through the first winter, then the next year we noticed some damp patches appearing in our corridor (with external wall). I then got the ladder out and spotted a tiny crack in the render. Can we repair this crack with paint or will it continue to crack after a couple of months. We want a permanent solution!
Hi Ann, our external wall insulation systems will help prevent penetrating damp – do you know what type of render was applied to your wall previously? Basically in order to get a permanent fix I recommend installing a new flexible basecoat layer (6mm thick layer of EWI-220 with embedded mesh – EWI 66640). This is then primed with EWI-333 and then rendered with Silicone Silicate Render (EWI-040). This will provide a flexible render layer that won’t crack! Give it a try!
We has new render put on our house 4 years ago and it quickly started falling off the wall. we then went with a Sto thin coat render system and it still looks perfect and better still the damp that used to appear in the corner of our room has completely stopped!
We have damp coming up the wall downstairs in our TV room. Would insulation help this or do I need to do something to the brick to stop the water coming up?
Hi DJ M Lead, I would suggest looking at sorting the rising damp prior to adding an insulation system. external wall insulation will stop penetrating damp damp, but it will not help prevent rising damp. You need to look at retrofitting a damp proof membrane; this can be done by injecting the brick with a damp proofing cream. The cream gets absorbed by the brick and creates a an water impenetrable layer within the brick so water can no longer be pulled up through the brick by capillary action.
We had sand and cement render on our walls and it had lots of little cracks all over it, but the EWI pro render seems to have stopped the damp nicely. Would recommend!
Thanks Igor.ravner, yes – the EWI Pro render systems when applied to the wall correctly should prevent any water ingress therefore preventing any penetrating damp. Rising damp needs to be treated prior to using our systems though, as this will not be helping by applying EWI / thin coat render systems to the wall.
I will literally try anything if it will get rid of the damp in my house… better start saving
I have been reading about the Silicone render on your website and I have noticed you call it self cleaning. How is this acheived?
Hi David Morris, the Silicone Render is self cleaning because it is hydrophobic – this means that when it rains, the rainfall hits the wall and flows off, taking with it any dirt. Basically it means the external wall insulation system is maintenance free – the façade remains clean and attractive,
We need to stop damp spots appearing in my daughters room.
Me and my boyfriend decided to get our house render as our house was literally infested with damp. Once our house got rendered there has been no damp in my house.
Our end of terrace solid wall ground floor flat has patches of damp appearing on external walls, mainly high up the walls and some round the bay window. We suspect penetrating damp. If we apply EWI to the external walls at ground floor but the upstairs flat (which doesn’t belong to us) is not treated, will that breach the insulation of our property?
Hi Judith,
Thanks for getting in touch. It is tricky to say to be honest. Applying solid wall insulation on your flat will prevent penetrating damp, however if water is making the walls damp above your property then gravity will pull that water down behind the insulation. You could help prevent this by installing a chemical DPC above the line where the insulation finishes, and also you could use a verge trim that is grinded into the wall to provide a mechanical barrier from the water coming down in the brick work. The verge trim does not go all the way into the brick work, so it would only stop water penetrating your flat if it was in the outer edge of the brick work.
In essence, it would be best if the whole property was done then you don’t have these issues!
This is a great article!
Our mid-terrace property has damp and mould patches on 2 areas of the external wall. The wall has pebble dash (painted) which looks like it was repaired sometime ago but has cracked again. It is quite obvious water has penetrated through there.
I am now looking to install EWI on all walls. My installer suggests to leave the render as is and install EWI on top. He says the render will add thermal mass to the wall. Is that correct or should I get the render removed back to the brick or get it repaired first?
My is the end of terrace and there is a lot of condensation the rooms ( water dripping from the wall, leading to damp) I do clean this nearly every week. Will it resolve the problem if I just render the external or do I have to use an insulation.
Hi Kele, just the render itself most likely wouldn’t resolve the problems with damp. You would need to install insulation as well as this keeps the walls warm which stops condensation. Hope that helps!
Did you get the black line on your exterior walls fixed I’m having the same problem here in Italy