How does external wall insulation work?

How does EWI work?

If you’re considering investing in an external wall insulation (EWI) system, you might have questions about how it works, and what impact it will have on your home.

The system

The most important part of any insulation system is of course the insulation itself. When it comes to choosing insulation, there are a number of types. A Weber recommended installer will be able to help you make this decision based on your projects requirements.

No matter what type you go for, EWI will dramatically reduce heat loss through the walls of your home. This means lower annual heating bills, and a more eco-friendly home. The system will keep your home warmer in the winter and cooler in the summer by keeping your solid walls condensation-free and protected from the weather.

Because the entire system is fitted outside, you won’t lose any internal space like you would if it was an internal system. It also means all the renovation works take place outside, so there’s much less disruption to your life, and no interference with your plumbing or electrics.

The fun bit

The best part of any home renovation is choosing a new finish! With through-coloured render, paint, or even brick-effect finishes on offer, an EWI system gives you the freedom to make the right choice for your property.

A new look for your property, and a cosier home, what’s not to love?  

The science bit

When it comes to calculating heat loss through a wall, we use something called a U-Value as an indicator.

All construction materials are measured for how they conduct heat, and this is called a Lambda value. When various materials are used together – like when constructing a wall – the combined thermal capacity is determined using a U-Value. The lower the U-Value, the more thermally-efficient the wall, meaning less heat loss.

When calculating a wall’s U-Value, the thickness and the materials – everything from the blocks to the cavity insulation – are taken into consideration. If we take a typical solid wall in a Victorian property, it’s likely to have an approximate U-Value of 2.1W/m2k. After applying a webertherm EWI system however, that value can be dramatically improved – as low as 0.30W/m2K, or even less. This number of 0.30W/m2k is the current target for building regulations in England, and is a good indicator of the kind of value you should be expecting after applying an EWI system.

Still got questions?

If you’d still like to learn more about EWI, you can read our frequently asked questions here.

Our technical team are also on hand to answer your queries (and even calculate your U-Value for you!), so don’t hesitate to get in touch:

Click Compare to help you choose the right product for your project, if you need further assistance please email