External Wall Insulation

Uninsulated solid walls lose heat at a rate of around 45%, meaning that for every £100 spent on heating an uninsulated solid wall property, around £45 is being wasted and escaping into the outside environment.

​The good news is solid walls can be insulated and it is one of the most effective home improvements that can be made, with typical savings on gas heating bills of £445 – £475 per year! If you use oil, electricity or LPG as your heating source then these savings can be considerably higher!

Most properties built before 1920 were constructed with solid walls – this accounts for around a third of homes in the UK. There are two ways of insulating a Solid Wall – either externally or internally.

Usage of External Wall Insulation (EWI)

This involves fixing an insulating layer to the outside of the house and rendering or cladding over the top. Render is generally the cheaper and most popular option. Cladding comes in a variety of forms including brick, tiles, timber or pebbledash. External Insulation is the preferred method of insulating. There are two basic kinds of solid wall: brick, which is typically 225mm thick, and stone which tends to be a lot thicker, and works in a different way.

Brick Walls

Rainwater will not penetrate as far into brick as it will into stone. The critical issue is the dew-point. When warm air meets cold air it condenses and moisture is released. In an uninsulated brick wall that point will be towards the outer surface of the wall. Insulating internally tends to draw the dew-point into the wall. What needs to be avoided is drawing it in to the inner surface of the wall – the best method of preventing this from occurring is to fit External wall insulation.

Stone Walls

A typical stone wall will be constructed of two skins of stone with the gap between filled with rubble. Render or cladding on the exterior of a stone wall can act as a waterproofer and will reduce the amount of moisture penetrating the wall.

FAQs about External Wall Insulation (EWI)

Planning Permission is not normally required for External Wall Insulation. However, if you live in a Conservation Area, a National Park, an Area of Outstanding Natural Beauty, or in a listed building, then Planning consent will be required.

External Wall Insulation suits a wide range of properties, both existing and new-build.

Although EWI has only really become popular in the UK within the last deacde (since the building regs were amended in 2010), it has been installed on properties in this country since the 1970s. However, in large parts of continental Europe, EWI has been used extensively since the 1950s. Therefore EWI is a tried and tested energy saving measure.

Building Regulations (Part L1B) sets energy efficiency requirements where more than 50% of an external wall (or more than 25% of the overall building envelope is being renovated). This means that whatever renovation you are undertaking to your wall, if it affects more than half the wall (or more than a quarter of the overall building envelope) you will need to add insulation to improve the thermal performance of the whole of that individual thermal element.

The most popular thickness is 100mm (4 inches) which is comprised of 90mm of insulation board and 10mm of basecoat and render. However, insulation boards vary from 20mm to over 150mm, so the choice is yours.

A wide choice of styles are available including a vast choice of colours, textures, pebbledash as well as real and simulated brick effect and timber effect finishes.

External Wall Insulation on average takes about 2-3 weeks from assembly to dismantling of the scaffolding. As with most external building works the installation is weather dependent.

The system will be installed in a number of key stages. All the external fittings will be removed or redirected, the insulation panels will be applied with a mechanical fixing, followed by the applications of a render system to provide protection and a decorative finish. Upon completion, all external fittings are then repositioned.

In order to comply with health and safety regulations, technicians will need to enter your property to carry out pre and post installation checks. These include assessing whether or not your home has adequate ventilation in place to prevent carbon monoxide poisoning and mould growth. They will not, however, need to come in to your home to use your electricity, as they will have their own generators. They will also not need to enter to use your water, but may however need to use your outside tap for mixing renders and cleaning up.

Some activities involved in the installation of external wall insulation are weather dependent and can delay the installation:

  • ​Very cold weather – anything below 5°C may mean that render cannot by applied as it is too cold for the render to set.
  • ​Very warm weather – could stop the top render coat from being applied as the silicone top coat can become too tacky to be applied smoothly. This is most likely to happen at temperatures over 25°C and on walls that are in direct sunlight.
  • Wet weather – the render top coat requires at least four hours to ‘set’. If rain is forecast during this time the installers may not be able to finish the property until they get a clear day to work on the property.

External wall insulation is generally maintenance free. The exterior finishes are designed so they do not allow the growth of mould. Maintenance should be limited to the need to wash down occasionally to maintain an “as-new” appearance

You will need to use fixings that penetrate through the external wall insulation and into the substrate of the building, i.e. the original wall to support heavy items such as hanging baskets.

Your external wall insulation system will withstand typical knocks and bumps. In the event that it is damaged by a very hard impact, repairs can be easily completed, such as with a normal wall.

All systems are tested by the BBA and NSAI for life expectancy and achieve a rating in excess of 30 years. EWI that was installed in Germany during the 1950s is still in situ today.

Yes, EWI does not reduce the floor area of your home; it will renew and improve the appearance of outer walls, improves weatherproofing and sound resistance and increases the life of your walls by protecting the brickwork. EWI will also increase the Energy Performance Certificate (EPC) rating of your property, which you are legally required to provide to a prospective buyer. The lower heating bills and increased comfort of an insulated property will also be appreciated by any potential home buyers.

A U-value is a measure of how much heat is transferred through a given material; the lower the U-value, the better the insulator it is.

Installing 90mm of external wall insulation on to a typical 225mm thick solid brick wall can reduce the U-value from around 2.70 W/m2K to around 0.29 W/m2K – which is better than most new-build properties!