Calculating the cost of an external wall insulation (EWI) system is not as simple a task as you might think; the price not only accounts for the insulation materials but also the installation of the system, labour costs, square meterage (for example, our reinforcement mesh comes in 50m rolls while a bag of EWI-220 Adhesive will cover 3m2 of the wall), the choice of decorative finish and so on. What’s more, not only do the prices vary, but some materials require fixings and some adhesives, which will also be included in the price. Therefore, the cost of your EWI system depends entirely on the needs of your project. So, how does one calculate the cost of their EWI system?
Calculating the cost of the External Wall Insulation Materials
At EWI Store, we have just the solution for you. Not only do we have an excellent team on hand who will be happy to provide a quote – simply give them a call with some rough measurements of the area that needs to be insulated, and they can quickly calculate the EWI materials you need using their expertise – but we also have a fantastic tool available at your fingertips.
Whether you have experience with external wall insulation or are keen to try it, our accurate, easy-to-use EWI materials calculator can help!
What is the EWI Materials Calculator?
The EWI Materials Calculator is an online tool that enables homeowners, installers, and architects to quickly and accurately calculate the correct EWI materials needed to meet their requirements for their next project. The calculator will ask questions to determine the system’s cost based on their needs.
The questions the EWI Materials Calculator will ask are as follows:
Information needed to calculate the cost of External Wall Insulation
At this point, you might wonder what information the materials calculator will need to generate a system quote. We will outline each of these below! Firstly, questions will vary depending on your interests: eco, premium, or standard. This relates to the decorative finish you want on your walls. A more advanced silicone render system will offer better performance but at a higher cost. For example, Premium Bio Silicone Render actively resists biological growth. Therefore, it is suitable for use near shorelines.
- Amount of metres squared needed
To calculate the square metres needed, multiply the width by the height of each wall you insulate. Do not subtract windows or doors; this will give you an incorrect result, as our calculator considers wastage in the final calculation.
- Choice of insulation material
- Insulation thickness
- Choice of Mechanical Fixings
- Amount of Corner Beads
- Amount of Stop Beads
- Amount and choice of Starter Tracks
So, you might be a homeowner looking to install external wall insulation or apply a fresh new render façade to your home, a solid wall insulation installer looking for an easy-to-install product (at a great price), or even an architect looking for a way to improve the thermal efficiency of an old property vastly. Whatever the reason, you have come to the right place, and you can be assured that the materials calculator will assist!
Costs of rendering per meter squared
Our renders will have different coverage rates depending on the thickness required and whether they come ready to use or as a dry mix. Therefore, we’ve developed a handy little table to break down the costs of each type.
| Render type | Size | Bag or bucket | Coverage | Cost per bucket/bag (ex. VAT) | Cost per m² (ex. VAT) |
| EWI-075 Silicone Render (1.5mm) | 25kg | Bucket | 2.4kg/m² | £70.65 | £6.78 |
| EWI-076 Premium Bio Silicone Render | 25kg | Bucket | 2.4kg/m² | £80.87 | £7.77 |
| EWI-077 Nano Drex Silicone Render | 25kg | Bucket | 2.4kg/m² | £122.49 | £11.77 |
| EWI-040 Silicone Silicate Render | 25kg | Bucket | 2.4kg/m² | £61.42 | £5.90 |
| EWI-010 Acrylic Render | 25kg | Bucket | 2.4kg/m² | £44.80 | £4.30 |
| EWI-747 NHL 3.5 Lime Render | 23kg | Bag | 15 kg/m² per cm thickness | £16.62 | £10.86 |
| EWI-090 Monocouche Render | 25kg | Bag | 25kg/m² | £10.99 | £10.99 |
| EWI-060 Mineral Render | 25kg | Bag | 2.5kg/m² | £30.56 | £3.05 |
Renders seldom work alone as you require basecoat, mesh, and beading to strengthen any system. These incur additional costs that need to be factored in. You can also insulate alongside renewing the facade, which is always advisable due to the savings. Depending on your home type, you can expect an EWI and render system to cost anywhere from £6,000 – £20,000. Whilst this is a very broad range, the table above demonstrates the fluctuations in cost depending on performance.
An average-sized semi-detached home (96sqm, three bedrooms) will likely cost £8,000 – £12,000.
The quick payback scale of installing EWI
Despite the price cap falling slightly between 2023 and 2024, it still sits significantly above pre-Covid and pre-fuel crisis levels. The current price cap as of April 2024 is £1,690. If you are on a standard variable tariff (default tariff) and pay for your electricity by Direct Debit, you will pay an average of 24.50 pence per kilowatt hour (kWh). The daily standing charge is 60.10 pence per day.
EWI systems can save anywhere from £700 to £1,000 on energy bills, which brings the payback scale to anywhere from 10-15 years. As a result, the energy bills you end up paying are more in line with pre-Covid levels and in line with European price caps. As always, we maintain that EWI is an incredibly shrewd investment.
Trade installers get fantastic prices and warranties on the system
You may also be eligible for our trade discount prices as an installer. You will get a BBA-approved external wall insulation system delivered directly to the site and the materials you need at a great price. As a trade partner, we can also offer system warranties provided the installers have completed our free training course. Be sure to sign up for our Trade Account for free to receive your discounts!
So, there you have it—if you need help calculating the material requirements for an EWI job, call or use our EWI Materials Calculator today!
13 thoughts on “How to calculate the cost of an External Wall Insulation system”
Should you leave cavity wall insulation in place if we want to add external wall insulation or remove it? Will the cavity carry cold draughts?
Hi Susan, if the cavity wall insulation is in place and it is not causing any issues, I would add the EWI on top. If there are any issues with the cavity wall insulation (damp in the house) then remove it!
I’ve had a couple of quotes from companies for the install. Do you know how much they should be putting on top for the pipework?
Hi Ameria, it depends completely on how much pipe work there is I’m afraid. But anything from £200 up to well over £1000 depending on quantity and the materials used.
Hi James, We are looking at getting solid wall insulation, and we are interested in buying the materials to do so from yourselves, but we are finding it hard to find an installer who operates in this manner. It seems all solid wall insulation installers want to offer the full package (materials and install), would you be able to recommend one? I have been recommended this type of insulation by a friend of mine who had it done a couple of years ago. She said it has made a tremendous difference to her home and they hardly need the heating on at the moment so I think it is something we will end up doing to our home. Your thoughts would be appreciated!
We are looking to insulate our house but we need to remove the pebble dash, is there a cost per m2, so we can giv e ourselves a rough idea of the cost before we start any of the works.
This is extremely useful. We were looking at insulating our end terrace property and had an EPC carried out. The EPC recommends solid wall insulation but puts the price between £4,000 and £12,000 which simply isn’t useful. It is interesting to know that most installers calculate prices based on the square meterage of the wall. We hope to get our insulation in March when the weather improves a little. Thanks for your help.
No problem Raymond. We have talked to DECC (and now BEIS) about this in the past. It is very difficult, because there is a such a massive variation in costs. I think to be honest if you try and use £100 per m2 as a rule of thumb you should provide yourself with a much more accurate quote. In terms of the materials, you are looking at about £25 per m2, scaffolding £10 per m2 and the rest is then down to the install cost. Installers costs vary considerably, but always get quotes and we don’t recommend always going for the cheapest quote. Solid wall insulation is difficult if you don’t know what you are doing – we have trained hundreds of installers over the years and the quality of the finish they can achieve really does vary greatly. When render is applied nicely to a building it can look like a million dollars and bearing in mind it is one of the first thing that people see when they turn up to your home, it is not something we would skimp on. Always go with recommendations from friends and family, or give us a call and we can normally recommend local installers. The GreenAge also offer a great installer map which has local approved installers – access this by clicking here.
Thank you for providing such information. This is very generous of you providing such vital information which is very informative.
could you recommend external wall insulation installer ?
Hi Emily,
Please can you let us know where you are based and we can send through some recommended external wall insulation installers.
If you are using this product over SIPS do you require a vapour barrier between the SIPs and the insulation
I own a Victorian 3 storey, solid brick, end of terrace house which I rent out. I cannot change the appearance of the front but the sidewall is perfectly flat with no windows, pipes etc. It seems to me that a first step to improving the insulation would be to put external insulation on this wall. The wall is 9.5m long and approx 8m high. Please could you tell me what the most cost effective solution would be eg what material I should specify and what the overall cost per sq m should be.