Frequently asked questions about external wall insulation.

We have tried to provide detailed answers to the majority of questions that we get asked about External Wall Insulation (EWI).

How much does External Wall Insulation cost?

There are many factors that apply to each individual house. The age, style and size of the basic building. Also when fitting EWI onto a property consideration is given to the type of insulation board material, the insulation thickness, the render and many different texture finishes. It can cost from £8,000 upwards depending upon these factors.

However the Cost of the work needs to be considered in context of the Savings from the reduced use of fuel.

To find out more, take a look at our guide to the Benefits of EWI.

Do I need planning permission to install External Wall Insulation (EWI)?

Under most circumstances the answer is no. Dealing with Planning permission issues are not difficult and DJM can assist with it.

Planning Permission is required if your home is Listed, in an Area of Outstanding Beauty or in a Conservation Area. It should be obtained before work is started. You may also need Planning Permission if you live in a terrace house and your external wall runs directly onto a public pavement as the extra depth to your wall may be viewed as an encroachment onto public space.

For the vast majority of circumstances EWI is not classed as an extension to the walls. However under L1B of the Building Regulations, the alteration to exterior fittings and fixtures requires a Building Notice to be sent to the Council. A Building Control Inspector will pop along on the first day to meet the installer and again at the end of the job to sign it off and give you an Approval Certificate.

What savings can I expect to get from External Wall Insulation (EWI)?

An EWI compliant system will lead to cost savings through cutting heat losses by around 35-45%.

The Energy Saving Trust, which is an independent organisation calculate that a typical 3 bed semi-detached house will use around £400 less in heating costs if a solid wall home has EWI insulation fitted to the correct standards.

Of course heating costs depend upon fuel prices at the time and these are set to continue to rise in the years ahead.

Heat loss will take the path of least resistance so it is very important to ensure loft and roof insulation is adequate and that doors and windows are draught proofed. Otherwise the gain from the EWI will be greatly reduced.

What is the U value and how is it relevant to my property?

The U value is a measure of how quickly heat escapes from your home. The lower the figure, the less heat escapes. A solid wall home will generally be around 2.0 whereas a new, well insulated home will have a U value of about 0.25 - which is almost ten times better!

UK Building Regulations set a target of 0.3 and if walls have a U greater than 0.7 then additional insulation is required.

How effective is solid wall insulation?

External Wall Insulation (EWI) is the most thermally effective way of insulating solid wall houses. DJM Exteriors install using the most affordable and accredited materials and systems.

Solid walls are described as “Hard to heat and hard to treat” and if you live in one of the 7 million homes in the UK with solid outside walls then you will appreciate the costs involved in trying to keep them warm in winter. EWI has made it “Easy to treat, cheaper to heat”.

What external wall insulation grants are available?

Firstly, the Government only charge 5% VAT which in effect is a 15% subsidy.

However there is the following scheme for grants available.

The Energy Company Obligation (ECO) is also available and payback is based upon energy cost savings. DJM can also access funding for ECO projects.

How could I calculate payback on my investment in this system?

When considering payback it is important to be both accurate and realistic in assessing returns on capital invested in external insulation. It is important to remember this is a long term investment although there will be immediate benefits in the short term. The house is warmer and requires less energy to maintain the temperature. The heater will switch on less often as the rate of heat loss is reduced. This means you will use less fuel (gas, electricity or oil) to heat your house. As an example the Energy Saving Trust say a typical three bedroom semi will save around £300 - £400 per annum.

In addition to reduced heating bills, ongoing maintenance to the outside walls is eliminated. Your home will increase in value compared with a similar property in the same area which has not been insulated.

One unknown factor which will affect the calculation is the rate at which the cost of gas, electricity and oil will continue to rise. Every family heats their home in the way that best suits them so savings, costs and therefore payback will vary a lot.

How is a solid wall insulated from the outside?

A layer of insulation material in the form of insulation boards is fixed to the walls. Three different types of insulation board are used: expanded polystyrene, mineral wool and phenolic. The layer of insulation is then covered with a special type of render. The finish can be smooth or textured and be the colour of your choice. This will cover the entire external wall of your property.

How can I tell if I have solid or cavity walls?

Most houses built after 1930 have cavity walls. You can usually spot cavity walls from the wall thickness and by the pattern of the bricks. Walls more than 260mm or abut 10 inches thick are probably cavity walls. If all the bricks have the long side showing, called ‘side-on’ there is probably a cavity. A mixed pattern, with some bricks showing the shorter end-piece are probably solid.

How long does it take to install EWI?

This depends on the size of your property and the weather. On a small property like a terraced house in the summer it can be completed in a week. However, a large property in late autumn could take up to 3 weeks.

Why should I insulate externally and not internally?

There are several advantages. The main advantage is that you do not lose any internal space as all the insulation is on the outside walls. There is no need to vacate the house or rooms whilst the work takes place, no need to move furniture and internal fittings and no internal redecoration is required. It allows thicker, higher performing insulation to be used resulting in warmer walls. A final advantage is the elimination of any risk of condensation and cold- bridging as the whole building is essentially wrapped in an insulating skin.

How is the insulation attached to the wall?

Insulation boards are attached to the wall using a special adhesive which is applied to the rear of each insulation board before being laid onto the wall in a staggered pattern. The boards are then further secured by being mechanically drilled and pinned to the wall. At the base of the wall the boards sit in a base rail set at the height of the damp proof course.

Once the insulation boards are in place they are covered with an initial base layer of a specialist polymer bonding render. A nylon mesh, to prevent cracking due to thermal expansion and contraction is embedded in the render. The render is then primed and a decorative, weather proof final coat applied. This whole process forms an incredibly strong bond with the external wall insulation board. However it has the ability to flex and breathe so that moisture is not trapped in the walls or in the insulation layer.