Exernal Wall Insulation

Most properties built prior to 1930 were constructed with solid walls, so they don’t have cavities that can be injected with insulation. These solid wall properties can be insulated with external solid wall insulation. The purpose of insulating in this manner is to slow the movement of heat out through the walls, thereby dramatically reducing heating demand.

The embedded video produced by us and one of our partners shows the typical external wall insulation installation process.
In most cases, homeowners get in a professional to install solid wall insulation; it is not normally considered a DIY job. Because the insulating process involves covering the original brickwork, the process can significantly alter the appearance of the property. Since the outside walls are highly visible, it is advisable to get someone who knows what they are doing to install it!

There are many types of insulation products that can be attached to the outside of the home: expanded polystyrene, mineral wool and phenolic resin (K5), woodfibre and even cork! Expanded polystyrene (known as EPS) is certainly the most popular, since it is the most cost effective means of carrying out the works. Phenolic resin (K5 boards) is used when space is a premium, since you can use less of this type of insulation to achieve the required U-value.

Mineral wool can also be used to insulate solid walls and some people choose it because it not only provides an open vapour system, but it is a great acoustic insulator. If it is picked for this reason, it is very important that no acrylic render is used to finish the project, since it is not breathable and therefore defeats the object!

You may choose to use woodfibre if you want the most breathable and natural insulation materials – however the system itself is very expensive compared to the EPS system.

External wall insulation must adhere to building regulations when solid wall insulation is installed on the external walls of the home, it must adhere to building regulations. In this case it is referring to the thermal performance of the insulation; the solid wall insulation must achieve a U-value of 0.30 watts/m2k. With expanded polystyrene, this means that at least 90mm of insulation needs to be used – but obviously the thicker the material, the better its insulating performance.

For example, according to our competent U-value assessor, James Alcock a typical solid brick wall would require 90mm of the EPS system to achieve the desired retrofit building regulations u-value. Whereas to achieve the same value only 60mm of the K5 insulation board & system would be required.

For mineral wool you need 110mm of insulation to achieve the required U-value and for the woodfibre insulation you would require 110-120mm of insulation to achieve the same energy efficiency standards.
External wall insulation sometimes needs planning permission
According to the planning portal, planning permission is not normally required for installing solid wall insulation, provided the external appearance of the property doesn’t change. If your property is brick and unpainted, changing its colour with render will require planning permission. Also, if the building is listed or is in a conservation area you should consult your local planning authority.
From our experience of installing solid wall insulation across London, it seems there is no standard approach to how the councils judge what is acceptable and what isn’t, so if in doubt, it is probably worth asking the question!

Firstly, if the property has an existing render, a render test must be carried out to see if it is strong enough to hold the insulation. If not, all the existing render will need to be removed prior to attaching the insulation to the brickwork. If the render test shows that the existing render is firmly held in place, the render can simply be smoothed, ready for the insulation to be applied directly on to it.
Another important step prior to installing any external wall insulation is to remove any pipework from the outside of the building. These will be reinstalled at the end of the process (and maybe extended in some instances as necessary); this is one of main reasons that the insulating process is expensive and time-consuming.
Applying the external wall insulation and finishing the process is relatively complex, but the basic steps are outlined below:

Insulating panels are fixed to the wall using adhesive mortar.
Plastic capped fixings are driven through the insulating panels and around their perimeter into the wall to tie the panels securely to the wall.

Mortar is then applied over the insulating panels and the fixings.
An insulating mesh is then sunk into the mortar to hold the panels in position.

The mortar is sanded and painted with primer to prepare it for the render

The Coloured render finish is applied (available in any colour).

As the insulation goes on the outside of your house, it is important that you get the finish that you want.