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. Since the outside walls are highly visible, it is advisable to get someone who knows what they are doing to install it!
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.
Mineral wool can also be used to insulate solid walls and some people choose it because it is breathable. 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!
Solid 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 mineral wool you need 110mm of insulation to achieve the required U-value and for the phenolic resin you need just 70mm hence it is popular where space is a premium.
Solid 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!
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:
- 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 render finish is applied (available in any colour).
Below you can watch a video where we demonstrate how solid walls are insulated externally:
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.
On the whole, the most cost-effective way of insulating your solid walls is to finish it with a simple white render. However there is a huge variety of finishes possible: smooth, textured or painted, tiled, panelled, pebble-dashed or finished with realistic brick slips.
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.
Cost and financing external wall insulation
The cost of solid wall insulation is roughly £100/m2, so it is not cheap. However, it can be really worthwhile in the long run. While government grants have now been wound down, there are occasionally local council grants available for eligible people, so it is worth checking. Also, some companies will offer finance.
Advantages of solid wall insulation
- The insulation will take the U-value of your walls down to just 0.3w/m2k, equivalent to a brand new cavity wall built today – therefore your heating bills will be significantly lower.
- Solid wall insulation stops penetrating damp.
- The insulation can improve the appearance of your home – especially if you are replacing pebbledash.
- It can also really help reduce noise entering the home, so if you live on a busy road it might be just the thing
- Since the walls get warmer, they act as a heat store so rooms will take longer to cool down.
For a more detailed look at the advantages of solid wall insulation please click here.
Installing solid wall insulation
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