External wall insulation is a great way to insulate solid walls. Solid wall insulation can be done in two ways: internal wall insulation and external wall insulation, but external wall insulation is often more popular. One of the reasons people opt for external wall insulation is so that they do not lose floor space within the home. Instead, external wall insulation makes the exterior walls of your home thicker by adding layers of render and insulation.
But how much thicker? Here's what you need to know.
As a form of insulation, it makes sense that external wall insulation makes your property larger. Think of it like a coat around the whole house! The insulation material itself is relatively thick, but the thickness of the insulation isn't the only thing that contributes to the overall thickness of external wall insulation. There are a number of layers that make up the final product, all of which have a part to play in how dense the wall insulation is, and subsequently, how much bigger it makes your property.
These layers and components include:
Take a look: Does External Wall Insulation Add Value To Your Home
The insulation materials used in external wall insulation come in the shape of boards. Normally, they are made of either polystyrene, mineral wool, or sometimes in newer external wall insulation, phenolic resin.
The purpose of the insulation layer is to prevent conduction. By preventing conduction, they reduce heat loss through the wall and successfully insulate the home. The boards of wall insulation are attached to the solid walls using direct fixings and adhesive to ensure they are on the existing wall firmly.
Primer in external wall insulation is used to help prevent water penetration. It is a waterproof barrier that prevents moisture penetration and build-up. In some cases, when installing external wall insulation, the primer also acts as a secondary external insulation material.
The glass fibre mesh in external wall insulation systems holds the primer in place while the external wall insulation system is being installed. It strengthens the primer by applying stress across the surface evenly, which helps to prevent cracks later down the line. It also helps to improve the impact resistance of the external solid wall insulation, protecting it from damage caused by weather, accidental impacts, and even vandalism. Finally, it helps to prevent cracking by lending flexibility to the external wall insulation, making the solid wall insulation last that much longer.
Explore further: How Long Does External Wall Insulation Last
The final coat is the render or cladding of your choice. This, to a minor degree, is another way of adding insulation. However, it is primarily used on external insulation to improve the appearance of a home. Render is largely decorative, although it does provide a protective layer to the external insulation.
Your render finishes or cladding finish can be any style, texture, and colour that you like. With plenty of options when it comes to types of render, there are near endless options. You can make your solid walls look like whatever you fancy!
Explore: Is Rendering A House A Good Idea
If external wall insulation always has the same layers in it, is it always the same thickness?
The short answer is no. There is an average thickness, which is 100mm. This is the thickness that many people will find their external wall insulation at. However, there are lots of different thicknesses of external wall insulation out there. It is actually one of the reasons that external wall insulation is so popular, especially over internal insulation, as there is much more freedom when it comes to the thickness. You cannot expand internal walls too much without dramatically impacting the property, no matter how much thermal mass you want to add to the home.
Different thicknesses of insulation will impact the thermal conductivity and thermal performance differently. For example, thicker insulating material tends to improve a property's thermal performance.
When we are discussing thermal efficiency and conductivity, we use U-values. The lower the U-value, the better the insulation and the worse the conductivity. With that in mind, here are some figures that explore different levels of insulation thickness in a property:
It would appear, at least from those averages, that the thicker the external wall insulation, the better. However, sometimes thicker insulation is actually incredibly impractical. Often, with thick insulation on your external walls, you will have to extend window sills, and it can lead to the windows and doors being compromised, rendering the entire insulation and the external wall insulation cost irrelevant.
As technology progresses, thinner insulation materials are being produced. For example, the Spacetherm Aerogel insulation material is only 10mm thick but boasts great insulation properties for solid walls. However, these new insulation materials are pricier than the older materials, so aren't as popular.
Generally speaking, external wall insulation systems do not require planning permission in order to be constructed, however, in some situations that is not the case. Usually, in places of outstanding natural beauty, listed buildings, or conservation areas, installing EWI systems requires approval from the local authority. In this case, brick slips and promises to recreate the original render with the new render tend to help get permission.
But, if you're considering installing a particularly thick external wall insulation system, you may find that your local authority is less keen to allow it. This might be because it changes the appearance of the street, or it may be because it extends your property past your property lines. In the case of the latter, building regulations may dictate that they are not able to permit non-traditional construction. This is generally for fire safety reasons.
Learn more: Does External Wall Insulation Require Planning Permission
Cavity wall insulation's thickness depends entirely on the thickness of the cavity walls. Alternatively, when you have external wall insulation fitted, this can be as thick as you need (assuming the correct planning permission is in place).
