Advantages & Disadvantages of External Wall Insulation

Whether it’s due to increasing energy bills or government drives to reduce carbon footprints, insulation is likely to be a common job for properties across the UK in the next decade. Insulation isn’t a one-size-fits-all job, though, so understanding different options will be crucial.

One of the less common types of insulation is external wall insulation. There are many reasons for this, particularly its cost and limited suitability. However, for some properties, insulating the external walls can be a great option and lead to huge savings!

The Advantages & Disadvantages of External Wall Insulation

External wall insulation involves adding a layer of insulation to the outside of a property, supported with adhesives, reinforcements and a final layer of render to give the appearance of a traditional external wall. This method of insulation is almost exclusively reserved for older buildings with solid external walls, as these buildings have fewer alternatives when it comes to adding insulation.

One thing to consider with external wall insulation that could be either an advantage or disadvantage is that it changes the outer appearance of your building. This could be good if you want a more modern and fresh appearance, but it could be a negative if you liked the older look and feel.

The Advantages of External Wall Insulation

There are many advantages to installing external wall insulation. Many of them are similar to other forms of insulation, but installing it externally, as opposed to inside the property, does come with some unique bonuses.

Insulation Improvements

First things first, external wall insulation, just as with other wall insulations, is a fantastic way of ensuring your home is adequately insulated.

Many buildings struggle with low levels of insulation, translating into big seasonal swings in temperature (insulation not only helps retain heat in winter but can repel excess heat during the summer). This often results in higher energy bills, particularly during the winter.

By upgrading a property's insulation through external walls, you get a more comfortable building for those who use it, along with reduced energy bills, which could help recoup the costs long-term.

No Lost Floor Space

One of the big benefits of external wall insulation is that you don’t lose any space inside the property.

The vast majority of insulation types involve taking up internal space – floor insulation often causes the floorboards to rise, while internal wall insulation can force you to bring all the walls inward. Because external wall insulation is only placed outside the property, none of the internal dimensions are changed.

Minimal Disruption

Because insulation often involves opening up the walls, floor or roof, these jobs are very disruptive for those using the property. External wall insulation, on the other hand, has next to no impact on the daily workings of the building.

Because external wall insulation basically involves adding insulating materials around the outside of a property, there is no need to access the inside or start dismantling parts of the construction. As a result, it can often be completed with almost nothing required of the property’s owner. 

The Disadvantages of External Wall Insulation

Of course, no major property work comes without some drawbacks, whether economic or otherwise.

Notably Expensive

The most important thing to note is that external wall insulation is one of the most expensive forms of insulation you can choose. This is influenced by multiple factors, including the amount of materials required to cover the building and the time it takes to install.

Quotes for external wall insulation jobs on semi-detached houses can come anywhere between £10,000 and £20,000, mainly depending on the size of the building. For comparison, quotes for cavity wall insulation in a semi-detached property are often between £1,000 and £2,000.

Limited Suitability

There are a few reasons why external wall insulation might not be suitable for certain buildings, including the cost barrier.

Because it’s expensive, external wall insulation is often reserved for buildings where other options, such as cavity insulation, aren’t available. This is usually solid-wall buildings built in the 1920s or earlier. However, buildings like this can often be listed properties, which usually restricts what changes you can make to their outward appearance.

As a result, external wall insulation can be something of a catch-22 situation – it’s best suited to older buildings, but if they’re too old and are now listed, this method isn’t an option.

Potential Damp Issues

Older buildings – which are the usual contenders for external wall insulation – sometimes have slightly porous stone walls. While not great for insulation, these walls are important for allowing moisture to pass out of the building.

When installing external wall insulation, depending on the exact materials used, you can inadvertently create a barrier around the building that traps the moisture inside. If the property doesn’t have adequate ventilation, this can create damp issues for the internal walls.

How to Decide if External Wall Insulation is Right for a Property

As a general rule, this style of insulation is only considered for older buildings with solid walls, where other options for insulation are limited. If you have a younger building with cavity walls, then cavity wall insulation is almost always the better option because it is much cheaper and doesn’t alter the appearance of the building in any noticeable way.

Even if you have an older building, there are still many reasons why you might choose another option. Internal insulation options can be cheaper and add up to similar insulation improvements.

However, if you have a smaller old property and are conscious about saving the internal space, and quite like the idea of giving the building an external makeover, then external wall insulation could be a great option. Government grants can also be explored to try to keep costs down.

It’s worth remembering, though, that every property and situation is unique, so the advantages and disadvantages of external wall insulation need to be assessed by professionals in each instance. Hopefully, though, this guide will give you some information to help you have a better and more informed conversation about the possibilities in each case.