Can I Install External Wall Insulation on a Cavity Wall?

At EWI Store, we receive many enquiries from homeowners who are very interested in installing EWI. However, there is often confusion as to whether it is possible to install EWI on a home with existing cavity wall insulation. In today’s post, we’re going to be tackling this question to see if we can clear things up!

What is Cavity Wall Insulation?

If your home was built after the 1920s, it’s likely that it will have been built with a cavity between the two exterior walls.

The main purpose of this cavity was to prevent damp crossing over from the outside through to the interior walls, but it wasn’t until later that people realised it could be used for another purpose. Nowadays, cavity walls are often retrofitted with an insulation material in order to increase energy efficiency and reduce the amount of heat lost through the walls.

In today’s housing stock, cavity wall insulation (CWI) seems to be the default method of wall insulation however, this isn’t to say that there haven’t been people with negative experiences of it. Damp and condensation have often been reported as a side effect of CWI, usually occurring as a result of cold bridges caused by poor installation. There are therefore many people who are quite rightly wary of CWI, so they instead look elsewhere for their wall insulation solutions.

What is External Wall Insulation?

If your home was built before the 1920s, then it’s likely to be a solid wall property. These properties present a bit of a challenge in terms of increasing energy efficiency because there is no cavity to fill, so homeowners either have to opt for no insulation (and high energy bills), internal wall insulation (IWI) or external wall insulation (EWI).

EWI provides the best solution for this type of building, as it is fitted onto the outside walls by securing the insulation boards with adhesive and fixings. A protective render is then applied to the insulation boards to create a weatherproof seal.

Unlike IWI where the thickness of the insulation is severely limited by how much floor space you can give up, EWI allows users to install insulation as thick as 200mm onto the outside walls of their properties.

Further to this, the effectiveness of CWI is dictated by the amount of insulation that can actually fit within the cavity – some cavities are just 50mm wide, so the benefits of insulating this are pretty slim.

EWI, therefore, offers increased potential for homes to massively up their efficiency. Unfortunately, it’s commonly assumed that homes with cavity wall insulation are: a) insulated well enough, and b) cannot have EWI as well as CWI.

To see what materials you will need and how much EWI may cost, visit our Materials Calculator Tool.

Can I have both EWI and CWI?

In fact, if you have CWI, then EWI is likely to reduce any problems with damp caused by the cavity wall insulation. This is because EWI completely envelopes your home in a weather-proof blanket, preventing water from entering through the exterior walls and keeping the temperature of the walls nice and warm. Because EWI wraps around the entirety of the exterior walls, there are no gaps and therefore thermal bridging is kept to a minimum.

So, because the internal temperature of the walls increases, the chances of damp and interstitial condensation are reduced. If there were any cold spots within the cavity wall insulation before, then the EWI will counteract the effect of these by maintaining a warm wall temperature.

If you currently live in a cavity insulated house and you want to upgrade the wall insulation even further, get in touch! We can talk you through the process and offer you our technical expertise.

 

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