Your Unbeatable Guide to Cavity Wall Insulation

Five minutes, that’s all you need. Five minutes and all of your cavity wall insulation questions will be answered. How much does cavity wall insulation cost? You won’t have to look any further than our blog. Do you want to find out if you qualify for a cavity wall insulation grant? Guess what, you can find out right here! From the costs of different cavity wall insulation materials, to how long cavity wall insulation should last, and even your most asked question… What is cavity wall insulation? Become an expert on one of the biggest investments you can bring to your home, in minutes.

To begin…

What is cavity wall insulation?

If your home is built after… let’s say, the 1930s, it is more than likely the external build of your home will consist of two walls, internal and external, referred to as a ‘leaf’, or ‘skins’. There is a gap in between these skins, this is your cavity wall! The cavity is normally 50-75mm in width. 

Cavity wall insulation is the installation of a material into this gap between the two skins.

Are you looking for a reason to have cavity wall insulation? Well, here’s 5!

If you want to be warmer in your home, here is your first reason. Cavity wall insulation raises the core temperature of your home. This is because of the reduced amount of heat escaping your home. Not only will this make you far more comfortable in your own home, but it will also be of benefit to yours, and your loved ones’ health. The dangers of living in a cold, damp home to your health are greatly underestimated.

Quick, clean, easy… the 3 magic words everyone loves to hear! Cavity wall insulation is a very non-invasive, relatively mess-free and speedy method of home improvement. Leaving your home looking neat, and warm in under a day.

Cavity wall insulation also reduces your carbon footprint. Unfortunately, if your home is powered by anything other than renewable energy, it really is greatly impacting our environment. Even more so, if the heat is escaping through your walls, because you’ll be overcompensating and keeping your heating on for twice as long! This would explain how cavity wall insulation really can reduce your carbon footprint. If there’s less heat leaving your home, your home will stay warm. No need to keep your heating on! 

It’s not the most expensive home improvement method… granted, cavity wall insulation isn’t ridiculously cheap. Having a warm, cosy home is priceless though, right? Anyway, cavity wall insulation really does end up paying itself off. That brings us to our last point…

If you don’t want to save money on your energy bills, don’t have cavity wall insulation. You could save between £145 and £480 per year with insulated cavity walls, depending on the size of your home of course, see our graph below.. This means your cavity wall insulation could have paid itself off in as little as 4 years! Don’t believe us? Check out the Energy Saving Trust’s blog on cavity wall insulation. 

What’s the most important question you should be asking if you’re thinking of having cavity wall insulation…?


How about…

Is your home suitable for cavity wall insulation?

This is, unfortunately, a question many households have forgotten to ask. It’s also a question many insulation companies won’t answer truthfully. Meaning, they have wrongfully installed cavity wall insulation knowing full well it may damage your home. So, just for you, on behalf of First Choice Energy Ltd, I will spill the beans. Not all properties are actually suitable for cavity wall insulation. 

Well, what properties should have cavity wall insulation?

If you live right by the sea, you probably shouldn’t have cavity wall insulation. Most properties by the sea are a subject of wind-driven rain. So what? So everything! When rain often pelts your walls (not unbelievable with our Great British weather) it gives rare opportunities for your walls to dry out. This means that there will be a moisture build up in your walls. The moisture will transfer to your cavity insulation, and damp and mould will begin to develop inside your walls. 

This really does become a hindrance for you when the mould starts growing inside your home, and damages your things. Not to mention the health effects mould in your home can bring.

Penetrating damp symptoms

A coastal facing gable end could be the deal breaker between you, and your cavity wall insulation. In the same sort of light as the seaside properties, having cavity wall insulation in your gable end is definitely the wrong choice. The gable end of your home is the side with the most wall surface area, where each side of your roof meets. In easy terms, the side of your home with the most cavity wall insulation. So, if it’s exposed to wind-driven rain from the coast, it’s more than likely to cause damp in your home, costing you more money than it’s worth.

If your home is timber, or steel framed, do not, I repeat, DO NOT have cavity wall insulation. Both of these structure materials need sufficient airflow, provided by the cavity of your home. Insulating your cavity reduces this airflow. “But why is airflow for these materials so important?”. Basically, the reduced airflow encourages the development of damp and condensation around these materials. 

So what? This won’t just cause damp and mould in your cavity and your home. It will eventually lead to wood rot with the timber frame and corrosion with the steel. Again, so what? This actually makes your home totally, structurally unsafe to live in. What’s more, if a surveyor comes to check your property, it will be deemed structurally unsafe. So, if you’re thinking about selling your home, forget about it! At least until the insulation has been removed.

The condition of your cavity is very important. Rubble and dirt in your cavity? Please have it removed before insulation. Your installer should recommend this (we will, anyway). Why’s this so important? Any rubble and dirt inside your cavity wall acts as a bridge for damp and moisture to invade the insulation, eventually causing damp and mould inside your home… this really isn’t something you want to deal with, trust me!

On the same note, if your cavity is less than 50mm in width, forget about it! Although insulation is to keep the warm air inside your home, it still needs to breathe. A narrow, insulated cavity is a recipe for damp, condensation and mould. No need to explain that again!

There are a couple of other minor details that can stand in the way of you and your cavity wall insulation… if you want to find out more, our article Is my home suitable for cavity wall insulation? Is the tell-all that you need!

Does this remind you of your home? You may want to start thinking about cavity wall insulation removal! You can book a free survey, with us right now, and start your home's journey to recovery!

How much does cavity wall insulation cost?

So, your home is suitable for cavity wall insulation, but is it worth the cost? Can you really put a price on a cosy, warm, energy efficient home? Where your children will feel safe and comfortable, and no one’s health will be hindered by cold walls and damp or mould?

The cost of having your cavity walls insulated does depend very much on a few factors. In short;

Detachment and the size of your home,

Does your home need scaffolding?

Does your cavity need extraction, or rubble clearing before the insulation takes place?

It goes without saying, the bigger your house is, or the larger square meterage of your home that you want insulated, the more it’s going to cost. So, your mid terraced home will cost less than someone else’s semi-detached. Or, your detached home is going to cost a bit more than other households’ end of terrace. It does also depend if you want all of your walls insulated too. If your detached home has a coastal facing gable end, and you don’t want it insulated, it will then cost 75% of the price for a 4 walled insulation, get me?

Does your home need scaffolding? Good question! Is your home more than 1 storey high? Yes? Then you probably will need scaffolding. Another reason you may need scaffolding is if your home has any add-ons like a conservatory or an orangery or something like that. With most cavity insulation companies, unfortunately, scaffolding isn’t included in the price, and can cost upwards of £300 to hire. What a time to live in a bungalow! 

I’m sure you’re aware that you can’t fill, or ‘top up’ a cavity that’s already been insulated, it can void your insulation guarantee provided by CIGA! Why does this matter? If your initial cavity wall insulation proves to be faulty, you will not be able to make a claim and have the insulation removed under the guarantee. But if you just decide you want a more up-to-date insulation material as opposed to mineral wool, unfortunately, you will have to pay for the extraction and the refill of your upgrade anyway. Here at first choice energy, our prices range from £16-18 per m² depending on the materials to be extracted. Which, (not to brag) happens to be a bargain in comparison to the larger scale cavity wall insulation/removal companies. 

Rubble removal from inside your cavity wall is, too, a small extra cost. To be quite honest with you, it’s pretty justified because it will probably take the same amount of time, and twice the effort of actually installing the insulation into your home.

What are the best cavity wall insulation materials?

What are you planning on putting in your cavity wall? The all important question! You won’t have to look any further than right here. Quickly, read your way through our expert guide to the best insulation materials for your home. Whether if you’re a first-time insulator, or having a refill after insulation removal. It really is best if you know the pros and cons of each insulation material, before you make that all important decision. 

Good for you to know: when you see a ‘λ-value’ mentioned, just know it’s the measurement used for the thermal conductivity of a material. I.e., how well a material can transfer heat. Obviously, you  don’t want the insulation material of your choice to transfer heat, so, the lower your ‘λ-value’, the better!

Mineral wool


The abundance of materials to make mineral wool is all but never-ending! This is because mineral wool insulation material is made out of igneous rocks, and sometimes glass and sand. These rocks are then heated up and spun into the wool, ready to insulate your cavity.

Because the materials to make mineral wool are natural, or recycled, this makes mineral wool the easiest insulation material to dispose of because of its recyclability. An eco-friendly material!

Cheap and easy? Yes! When it comes to installing your insulation materials, these are the three magic words you want to hear. Mineral wool slides easily between the leaves of your cavity at a low cost of £10-£15 per m² (not including labour, though). 

With a lambda value (λ-value), of around 0.034 W/mk, mineral wool is a very good insulator for your home (remember, when it comes to λ-values, the lower, the better).

Despite all these great things about mineral wool, the material does actually have a completely different side to it (cue the dramatic music)…


Before having mineral wool installed in your home, your cavity must be clean!!!!!! And considered ‘spacious’ (50-75mm). The clearing of a cavity wall can be an expensive job to have done… but if you’re considering insulation, it’s completely necessary. Why’s this? Stuffing mineral wool can be a massive hindrance to your home (explained in the next point).

The ultimate dealbreaker! Mineral wool can clump inside your walls, around the brick ties, causing cracks in your external wall, leading to water ingress. Oh, and it can cause dampness, just by being true to itself. Whenever someone has sold you a ‘water resistant’ mineral wool insulation material, they’ve also sold you a pack of lies. Let me tell you, a fair few of our extraction jobs have ended up with chronic dampness in their homes because of these lies. Mineral wool will gather moist air inside your cavity, making your walls damp, and even in some extreme cases, causing damp and mould. Taking into account how damaging damp and mould in your home can be to your health, the pros to mineral wool are pretty much void, and shouldn’t be recommended to you.

On to the next…

Polyurethane Foam (PUR)...

 …or as i like to call it, poly’EW’rethane foam.

For pure unbiasedness, just for your benefit, I will tell you the pros of this material. 


PUR isn’t a bad insulator for your home. A λ-value of approximately 0.030 W/mk actually makes it the best insulation material for your home. Meaning less warm air will be lost through your walls, costing you less on your energy bills (don’t let this reel you in).

Still, PUR is a pretty cheap material to have installed between the leaves of your walls. Although it’s not the cheapest, £20-£25 per square metre isn’t bad at all, not the cheapest though, is it?

That is pretty much it for the pros of PUR. 


Now, for the juicy gossip. PUR can actually shrink over time, no matter what any installers tell you. When it shrinks, it can allow water to enter your cavity wall. So what? This will cause severe damp and water damage to your home, costing you SO much money to have it extracted, and the damages repaired. NOT to mention, foam insulation is actually the most expensive material to have extracted.

Not only that, but when the materials shrink, quite obviously, so does the insulating performance, costing you more YET again, just this time, on your energy bills!

Lastly, sometimes, you have to think outside the box… PUR will fill every corner of your cavity. Good news, yes? No! At First Choice Energy, one of our many passions is educating our customers (you) on the best improvements for your home. Filling your cavity from wall to wall across its width is NOT the best option. It is not stressed enough to you how important it is to allow air to circulate in your cavity, enabling it to breathe and keep dry, to eliminate any chances of damp and mould developing. This will then save you the hassle of having to deal with these pests later.

What material is next..?

How about Polystyrene beads?

These are also known as ‘expanded polystyrene beads’, or EPS.


These little carbon beads are easy and cheap to install! Their lightweight and durable structure make for a quick install at around £10-15 per square metre, and it’s easy for the installer to perform this installation in comparison to any of the other clumpy, heavy materials. 

Yet another benefit of having EPS installed is that they come with a bonding agent. This means that it’s not just loose polystyrene beads inside your walls, they are stuck together by a long-lasting glue, i.e., the bonding agent. Again, this makes it an easy install, contributing to the low cost of EPS for your home!

When your polystyrene beads are installed correctly into your cavity, with the bonding agent, they are actually pretty water resistant! This is because they have a low absorption ability. What does this mean? It means, if water does somehow enter your cavity, the materials can dry out pretty well because the moisture can’t be absorbed or cling to the material. This also reduces the risk of developing damp and mould in your cavity walls. 

The insulating performance of EPS goes between the 0.030-0.034 W/mk mark. A very good insulator and money-saver for your home, don’t you think? 

What else can it do?! Well, your polystyrene bead insulation is also recyclable! After any unused carbon bead is sent to a recycling depot, and after being broken down into its original products, it’s fashioned into many things you could be using on a daily. Like what? Any polystyrene coffee cups, and even the trays in your refrigerator! 

As I’ve said before, for your benefit, you will be provided with both pros and cons.


A given- your cavity needs to be clear, clean and spacious! Much like the rest, a clean cavity with a width of about 50-75mm is perfect for insulation. As you’ve read before, though, it can be pretty expensive to have your cavity cleared. You have to understand, however, that this is such an important deal breaker in how much of an asset insulation will be for your home.

EPS can cause some problems if theyre not installed properly. Human error does occur from time to time! Needless to say, though, it’s not ideal when it does. If your polystyrene beads have been installed with the incorrect ratio of bonding agent it will cause problems in your home. An example includes- if your cavity is exposed at any point, and there’s not enough bonding agent, the beads will just fall out, making a mess in your lovely home. This is why it’s so important for you to hire an experienced, good company to install this for you… hint hint, US!

After a very good few years, facing a lot of wear and tear, sometimes the bonding agent and beads will pull away from your cavity wall. This means some heat can escape your home, and your house is at risk of developing damp and mould. It really is one of those unavoidable things, but another stress on why it’s important for you to hire the right company to insulate your home. A good insulation should last you years!

Why should you choose EPS beads as your insulation material?

From the perspective of a professional, experienced, and trustworthy company (us). Any material is going to have its pros, and its cons. However, the pros of EPS beads, and how much of an asset it will be to your home, really do greatly outweigh the superficial downsides to this material. As you have read, the cons of EPS beads are either the result of human error, or are pretty superficial, and can be managed quite well even before the insulation material is installed. (I’m talking about the clearing of your cavity wall, if it’s full of rubble, that is).

Now, obviously the decision is completely up to you, but if installing polystyrene beads is on your list of home improvements, why not get in touch with us today? You could have a free survey and a quote and your insulation installation appointment booked all in the matter of a few days!

Back to the article...

How to install cavity wall insulation

Tiny little drill holes are made in your outer walls to begin with, around about the diameter of a ten pence coin. These small holes are situated at about 1m intervals along your outer walls. Using some special equipment, the EPS beads and the bonding agent (at the correct ratio) are blown into your cavity through these holes. The holes are then re-filled with mortar as similar as possible to your own, so that they are barely noticeable. The result? you’re left with a warmer home, and with reduced heating bills!

Just to be clear, you probably shouldn’t do it yourself! You are more than welcome though, to get in touch with us though, and have your home insulated professionally by yours truly.

An UNMISSABLE opportunity- two ways you can get FREE cavity wall insulation

One of our many priorities as one of the UK’s best energy saving, eco-friendly companies is trying our best to provide you with the most effective methods of energy (and money!) saving. All of which, at either highly competitive prices, or through a government funded scheme. (Just to clarify, the methods of energy saving include; cavity wall insulation, underfloor insulation, external and internal wall insulation… things like that!). 

The ECO4 government grant scheme. 

This scheme is designed for those of you receiving financial support from the government. Be it Personal Independence Payment (PIP), Universal Credit, Armed Forces allowance, and more! For you to qualify, you must be in receipt of a certain allowance from the government. The process of your new energy saving measures is as follows;

One of our surveyors will come and have a look at your home, have a look at which measures can be applied to your home, and double check your credentials (see if you’re receiving the qualifying benefits). Then, you can pretty much leave it to us! Within 2 weeks you could have a new heating system, and you could be en route to saving hundreds each year on your energy bills.

The LA Flex grant scheme-You don’t receive financial support? Don’t worry, we’ve got you!

This is a grant scheme funded by your local council! Certain counties offer this, and if we work within these counties using their LA Flex, then you can get an energy efficiency method grant too! 

Once again the method of your application for this unmissable opportunity includes one of our surveyors coming to see which measures can be applied to your home to save you some money, and, again to check your credentials (see if you’re in a county that has an LA Flex scheme). What’s next for you? Relax! The rest is down to us. From installing your measures, to completing the submission documents, you won’t have to lift a finger… 

When you choose First Choice Energy Ltd...

…as your cavity wall insulation specialists, not only will you be provided with the highest standard of work, but you will also have some of the most competitive quotes in Wales and England. It doesn’t stop there, you can even give a friendly member of our staff a message if you have any queries or you’re looking for some advice. Click here to go to our contact page, one of us will get back to you within the day!