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U-values and Insulated Render Systems

Last modified: 03.12.2024
External wall insulation being installed on a detached property with scaffolding in place. High-performance mineral wool boards from EWI Store deliver superior fire resistance, soundproofing, and thermal efficiency.

Our insulated render systems are a great way to help improve the thermal comfort of your property by lowering the u-values. They are also a great way to reduce energy bills – less heat escaping through the walls means your boiler needs to work less hard. 90mm of our graphite-enhanced expanded polystyrene (or EPS as it is more commonly known) can halve the heating part of your energy bill. Couple this with the fact that many older solid wall properties are damp; wrapping your home in a watertight, insulated render system can significantly improve the internal environment – providing a drier, more comfortable dwelling.

Part L of the Building Regulations stipulated that certain targets must be met when improving existing building fabrics (like walls) or when building a new property from scratch. The target for insulation is known as the u-value, which shows heat loss for a given wall.

In the domestic sector, there are 3 targets that people need to be aware of

  1. Installing insulated render systems on existing properties;
  2. Installing insulated render systems on extensions on existing properties;
  3. Installing insulated render systems on new builds.

If you are adding insulation to existing properties (i.e. Target 1 and Target 2), you are only required to hit the targets if you are installing the insulated render system on more than 25% of the entire surface of the property.

This means that if you are trying to improve just a small part of the house, such as the walls of an exposed cold bedroom, then you can potentially add as little insulation as you want (provided this is less than 25% of the total wall area).

Now, without going too much into the maths behind the u-value target – every building fabric has an existing u-value or a level of heat loss. If you add insulation to the building fabric, there is less heat loss, so the u-value decreases. The targets set by the Building control can be used on every type of wall; the starting u-value will be different, and therefore, the amount of insulation required to hit the target will vary.

To keep things simple, we will concentrate on solid brick walls—a very typical building construction in the UK—since they can’t be insulated with cavity wall insulation—a common building type that gets fitted with our insulated render systems.

An existing 225mm solid wall has a starting u-value of 2.16 W/m2k.

  • When installing render systems on existing properties, the target u-value that needs to be reached is 0.30 W/m2
  • When installing render systems on extensions on existing properties, the target u-value that needs to be reached is 0.18 W/m2
  • When installing render systems on new builds, the target u-value that needs to be reached is 0.18 W/m2

So, what thickness of insulation will achieve this? Well, it varies depending on whether you are using mineral wool or EPS.

  • To hit a u-value of 0.30, you require 90mm of EPS or 110mm of mineral wool
  • To hit a u-value of 0.28, you require 100mm of EPS or 120mm of mineral wool
  • To hit a u-value of 0.18, you require 190mm of EPS or 210mm of mineral wool

Obviously, it is worth pointing out that nothing is stopping you from beating the targets! If you want to add 300mm of insulation to your extension and take the u-value down to 0.12W/m2k, then there is nothing stopping you do it! At EWI Store, we can source EPS at any thickness between 20mm and 400mm!

We also stock Kingspan K5 insulation in various thicknesses. Kingspan K5 is often referred to as a space-saving system because it can achieve the required U-values at much lower thicknesses, which makes it well-suited to spaces between houses or down alleyways. You will require 60mm of K5 to achieve a U-value of 0.30 W/m2.

Another key benefit is the protection they provide to the building's exterior. The render acts as a shield against weathering, preventing rain, wind, and frost from damaging the underlying structure. This reduces the risk of cracks and structural wear, extending the building’s lifespan. Additionally, insulated render systems can help prevent issues like condensation and mould by keeping walls warmer and less prone to dampness, which is particularly beneficial for older or non-standard constructions.

From an aesthetic perspective, insulated render systems allow for a wide variety of finishes, colours, and textures, giving homeowners and developers the freedom to achieve a desired look while enhancing the building’s energy performance. Whether blending in with traditional architecture or achieving a modern, sleek façade, these systems offer incredible design flexibility.

Finally, they contribute to environmental sustainability. By reducing energy consumption, insulated render systems lower a property’s carbon footprint, supporting efforts to combat climate change. Moreover, when combined with other energy-efficient measures, they can help properties meet increasingly stringent building regulations and secure higher Energy Performance Certificate (EPC) ratings, boosting the property’s market value.