When it comes to insulating your home, the thickness of the insulation material plays a crucial role in determining its effectiveness. Choosing the right insulation thickness can help you meet the U-value regulations for both retrofits and new builds while also providing long-term energy savings and thermal comfort. In this blog post, we’ll discuss U-value regulations, the ideal thickness for different insulation materials like EPS, mineral wool, and phenolic insulation, and the problems that may arise from not having thick enough insulation
UK building regulations
In the UK, building regulations play a crucial role in ensuring the energy efficiency, safety, and structural integrity of buildings. These regulations set standards for the design, construction, and alterations of buildings, including the installation of external wall insulation.
For external wall insulation, UK building regulations primarily focus on the following aspects:
- Thermal Performance (U-values) – Building regulations set specific U-value targets for new builds and retrofits to minimise heat loss and improve energy efficiency. These targets can vary depending on the country and region within the UK.
- Fire Safety – EWI materials must meet specific fire safety standards outlined in the building regulations. These regulations aim to minimise the risk of fire spread, especially in multi-story residential buildings. Materials like mineral wool provide excellent fire resistance properties.
- Condensation Control – Building regulations require that insulation installation should minimise the risk of condensation, both on the interior and exterior surfaces of the building. Properly installed insulation helps to maintain a consistent temperature and humidity level inside the building. In turn, reducing the risk of condensation and potential mould growth.
- Ventilation – Installing external wall insulation may affect the ventilation of a building. Building regulations emphasise the importance of maintaining adequate ventilation to ensure a healthy indoor environment.
- Structural Integrity – EWI can add weight to the building structure. As such, it is essential to ensure that the building can support the additional load. Building regulations require that structural assessments be carried out before installing external wall insulation to verify that the building can safely support the new insulation system.
- Planning Permission and Building Control Approval – You may require planning permission to install EWI, especially if the building is listed or located in a conservation area. Additionally, you will typically need building control approval to ensure the insulation work complies with the building regulations.
U-value regulations
U-value measures the rate of heat transfer through a building element, such as walls, windows, or roofs. The lower the U-value, the better the insulation properties. Therefore, less heat is lost through the building element. Both retrofits and new builds must adhere to U-value regulations to ensure energy efficiency and minimise heat loss.
| New builds | New elements in existing dwellings | Existing elements in existing dwellings | |
| Roofs | 0.11 W/m²K | 0.15 W/m²K | 0.16 W/m²K |
| Walls | 0.18 W/m²K | 0.18 W/m²K | 0.30 W/m²K |
| Floors | 0.13 W/m²K | 0.18 W/m²K | 0.25 W/m²K |
These values allow one to calculate the thickness of insulation you require. If you know the nature of the substrate, you can calculate the U-value of this and then determine the thickness required. The thickness will vary depending on which type of insulation you choose. EWI Store offers Mineral Wool, EPS, and Kingspan K5 which is a form of phenolic insulation.
The ‘best’ EWI thickness
It is difficult to qualify the best EWI thickness as it depends on the substrate you are working with! A brick wall will have a much higher U-value than ICF for example, therefore, a greater thickness if required. We do recommend a certain thickness for each insulation material.
EPS is a lightweight and cost-effective insulation material. To achieve a U-value that meets most building regulations, the thickness of EPS insulation should generally be between 90 and 150 mm (3.5 to 6 inches). The exact thickness required depends on the specific EPS product used and the existing wall construction. At EWI Store, we tend to say that 90mm will achieve a U-value of 0.3 W/m²K.
Mineral wool is a popular choice for external wall insulation due to its excellent fire resistance and soundproofing properties. The thickness required for mineral wool insulation to reach optimal U-value regulations typically ranges between 100 and 200 mm (4 to 8 inches). At EWI Store, we tend to say that 110mm will achieve a U-value of 0.3 W/m²K.
Phenolic insulation offers the highest thermal performance of the three materials mentioned here. It is a rigid foam insulation with low thermal conductivity, making it highly effective at reducing heat loss. To meet U-value regulations, phenolic insulation typically requires a thickness of 60 to 130 mm (2.75 to 5 inches). At EWI Store, we tend to say that 60mm will achieve a U-value of 0.3 W/m²K.
What if your insulation is not thick enough?
If the insulation installed in your building is not thick enough, it can result in a variety of issues that negatively impact energy efficiency, compliance with regulations, and overall comfort for occupants.
Firstly, insufficient insulation thickness can compromise the building’s thermal performance. Poor thermal performance leads to greater heat loss, which in turn results in increased energy consumption and higher heating bills. By ensuring that your insulation is of adequate thickness, you can enhance the building’s energy efficiency and save on energy costs.
Secondly, failing to meet U-value regulations due to inadequate insulation thickness can lead to non-compliance with building codes. Non-compliance may result in fines, potential legal complications, and even the need for costly remedial work to bring the building up to code. It is essential to consult local building regulations and guidelines to determine the appropriate insulation thickness required to meet U-value targets and avoid such issues.
Thirdly, a building with inadequate insulation may experience drafts, cold spots, and temperature fluctuations, which can significantly reduce indoor comfort for occupants. These issues can make living or working in the building less pleasant and may even have long-term implications on the occupants’ well-being. By choosing the right insulation thickness, you can ensure a more consistent and comfortable indoor environment.
Lastly, insufficient insulation can contribute to the formation of condensation on walls, which may lead to mould growth. Mould growth not only damages the building structure but also poses potential health risks for occupants, especially those with allergies, asthma, or compromised immune systems. By selecting the appropriate insulation thickness, you can minimise the risk of condensation and mould growth, ensuring a healthier living or working environment.
