There seems to be a bit of a gap in information out there about whether it is possible to install external wall insulation (EWI) onto a flat, so we wanted to answer this question for you and provide as much information as possible for any flat-owners who are considering EWI!

In most cases the answer is yes, you can install EWI onto a flat. However, usually the insulated render system is sealed at the top where it meets the soffit of the roof. So, on a groundfloor flat the insulation must be sealed at the top by other methods. This is because if it isn’t sealed, the exposed edges of the insulation can allow for water to seep behind the back of the insulation boards which can in turn effect the integrity of the EWI system, and water can then also enter the property through the walls causing problems with damp and mould.

We would recommend that EWI is most ideal for people who own a ground floor flat. This way, the EWI is at least sealed at the base so to prevent too much heat loss and water ingress, and the EWI will most likely be less noticeable.

So how do you install external wall insulation onto a flat?

Installing external wall insulation onto a flat is a slightly different process than with a normal house. This is because if the top of the insulation is exposed, i.e. does not meet the soffit of the roof, then certain actions will have to be taken to ensure that the EWI on your flat is water-tight.

There are a few options to consider in order to achieve a water-tight finish:

With the upper ledge of your insulated render system exposed, you will always need to use a verge trim to protect the EWI from water exposure. One option is using a basic verge trim which screws into the wall above the EWI. However, this is not entirely water tight because the top of the verge trim is not sealed, so you will need to use a sealant along the upper edge of the external insulation to prevent water running down its back.

The second option is using a Grind-in verge trim. As the name suggests, this is a verge trim with the length of its upper edge inserted into the wall surface. However, you have to first damage the surface of the existing wall to insert the verge trim, and the result is that it’s still not completely watertight. This method is therefore still a bit risky.

We suggest that the best option is to use lead flashing with a normal verge trim. This doubles up the waterproofing so that the lead flashing protects the verge trim, and the verge trim protects the top of the EWI.

As for the base of the external solid wall insulation, if it’s exposed (because your flat is not on the ground floor), then we recommend the use of white PVC so that it will look nicer for your neighbours below to look up at.

Pro’s of installing external wall insulation onto your flat

EWI is a great way to save energy on your heating bills. Most flats have electric heating, which is far more expensive than gas heating. This means that heat loss through the external walls of a flat is much more problematic for you as the homeowner, because you then need to spend even more money on re-heating the flat. EWI can dramatically reduce the amount of heat being transferred through the walls of your flat and save you a lot of money on energy bills every year.

As well as this, people who live in flats are often in a more built up area which suggests more noise from road traffic. For people living on ground-floor flats this is potentially more of an issue and can be exceedingly unpleasant, so installing insulated render can greatly improve the amount of noise that enters your home.

People living in flats are also the most likely candidates to be struggling for space. EWI takes up absolutely none of the internal floor space, which means that your property will not lose any value due to a decrease in the size of its rooms and you will still have plenty of moving around space!

Cons of installing EWI onto your flat

If you install external wall insulation onto your flat, depending upon the thickness of the insulation boards, it could mean that the external walls of your flat will physically stand out from the rest of the building and the necessary verge trim may not be a particularly attractive feature to look at. Also, depending upon the external walls of the rest of your building, you might need to spend more to ensure that your render matches the overall look of the building. There are a number of ways you can do this, for example we offer a variety of very realistic looking brick slips which could work really well at blending the EWI on your flat in.

Most flats are lease-hold only, so you would likely need to ask for permission to install EWI, which is potentially a long and difficult process. It can be an expensive job for a small property and is not guaranteed to be as energy efficient as if you were to insulate an entire house, for example. Also, you will have increased scaffolding costs if your flat is on an upper level.

People who live flats live in very close quarters with their neighbours, so any work being done to your flat is likely to be more disruptive. Upset neighbours may therefore complain about any disruption during installation time, and may not be all too pleased with the finished look.

The best thing to do when considering an EWI installation is to seek professional advice. We recommend that you hire a surveyor to discuss the feasibility of installing EWI onto your flat. Our staff are all extremely knowledgeable about EWI, and are always happy to help in any way. For any enquiries, please do not hesitate to call us here at EWI Store.