Why choose solid 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.

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. 

There are three types of insulation that can be attached to the outside of the home: expanded polystyrene, mineral wool and phenolic resin. 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 is used when space is a premium, since you can use less of this type of insulation to achieve the required U-value.

How is solid wall insulation installed?

Firstly, if the property has 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 insulation and finishing

The process is relatively complex, but the basic steps are outlined below:

1. Insulating panels are fixed to the wall using adhesive mortar.
2. Plastic capped fixings are driven through the insulating panels and around their perimeter into the wall to tie the panels securely to the wall.
3. Mortar is then applied over the insulating panels and the fixings.
4. An insulating mesh is then sunk into the mortar to hold the panels in position.
5. The mortar is sanded and painted with primer to prepare it for the render
6. The render finish is applied (available in any colour).

What finishes are possible?

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

External solid wall insulation and damp

External wall insulation is a great way to protect against penetrating damp, creating a new weatherproof layer on the outside of the building, and slowing the movement of heat through the walls. Another advantage of solid wall insulation is that it will cause the temperature of the walls themselves to rise. This means if there is lots of water vapour in the air (from cooking or washing for example), this will no longer condense on these walls.

While obviously this is a benefit, it is still important to consider ventilation in the home – regardless of whether you insulate or not. This can be done by installing more vents or by making behavioural changes like opening windows and doors while cooking.