Choosing the right thickness of insulation boards is one of the most important decisions when you want to make your home energy efficient. Whether they are for floors, walls, pitched or flat roofs, the required thickness of insulation boards has a direct impact on heat loss, comfort and energy costs. In this guide, we explain how to determine the right insulation thickness for different applications, why insulation board thickness is crucial, and how to choose the ideal insulation based on the Rd value.
Why is the thickness of insulation boards important for good thermal insulation?
The correct thickness for insulation boards determines how well insulated your home is. Thicker insulation boards offer higher thermal resistance (Rd value), resulting in less heat loss and lower energy costs. This not only results in a more comfortable indoor climate, but also contributes to a sustainable and energy-efficient home. As well as thermal insulation, thicker insulation layers often have an additional benefit: better sound insulation.
Insulation has to be tailor-made
Insulation is a process which is unique to each building or home. There are several factors that affect insulation, such as the size and shape of the building, the choice of materials and the climatic zone in which the building is located. For that reason it is important to use a professional insulation specialist who can assess the specific needs of your project and recommend the right insulation solution. A specialist can help you choose the right thickness of insulation boards, taking into account the lambda value and the desired thermal insulation. This ensures that your home is not only energy-efficient, but also comfortable and sustainable.
Determining the right thickness for your insulation
- Assess your situation: check whether you are dealing with a new construction project or a renovation. In new buildings, insulation standards are often stricter, while renovations require more flexibility.
- Determine the desired Rd value: the Rd value (thermal resistance) is a measure of the insulation value of a material. The higher the Rd value, the better the insulation. PIR boards are known for their high Rd value per centimetre and therefore often offer better performance than other insulation materials.
- Check the space available: not every room offers the same opportunities for thick layers of insulation. For example, with floor insulation, you need to consider the available space under the floor, and with roof insulation, the type of roof can affect the roof insulation thickness you can install.
- Comply with building regulations: the insulation thicknesses you choose should comply with local building regulations. In Flanders, for example, a roof must have a minimum Rd value of 6 m²K/W, which corresponds to a certain insulation thickness, depending on the material.
Types of insulation
There are different types of insulation that can be used, each with their own unique properties and benefits. Some of the most common types of insulation are:
- Mineral wool: This is a popular insulation material known for its high insulation value and fire resistance. Mineral wool is flexible and can be easily adapted to different shapes and surfaces.
- Insulation boards: Thin, flat panels that can be used to insulate walls, floors and roofs. They are available in different materials, such as PIR and EPS, and offer a high insulation value per centimetre.
- Insulation blankets: Flexible, roll-shaped insulation that can be used to insulate irregular surfaces. Insulation blankets are ideal for insulating attics and crawl spaces.
- Blow-in insulation: A type of insulation that is blown into the cavity wall to improve its insulation value. Blown-in insulation is particularly suitable for renovation projects where the existing structure needs to be preserved.
Thickness of insulation boards by application
The thickness of insulation boards varies depending on the application and the desired insulation value. It is important to choose the right thickness of insulation material to meet legal requirements and BEN standards. Below is an overview of recommended insulation thicknesses by application:
| Application | Recommended thickness of insulation boards | Notes |
|---|---|---|
| Floor insulation thickness | 6 - 12 cm | The ideal thickness depends on the desired insulation value and the space available under the floor. |
| Internal wall insulation thickness | 8 - 14 cm | Internal walls often require thicker insulation to reduce heat loss, especially in older buildings. |
| Facade insulation thickness | 10 - 16 cm | For external applications, thicker insulation is needed to meet modern energy standards. |
| Thickness of roof insulation (pitched roof) | 12 - 24 cm | Good roof insulation is essential, as heat is quickly lost through the roof. |
| Thickness of roof insulation (flat roof) | 14 - 20 cm | Flat roofs require a thicker layer of insulation for better thermal performance. |
Minimum thickness for optimal insulation
The minimum thickness for optimal insulation depends on the type of insulation and the specific needs of your project. In general, a minimum thickness of 10-15 cm is recommended for mineral wool and insulation boards, and 5-10 cm for blown-in insulation. However, it is important to follow the manufacturer’s specific recommendations and local building regulations. By choosing the right thickness, you ensure good thermal insulation and a high insulation value, resulting in lower energy costs and a more comfortable indoor climate.
How do you calculate the right thickness?
To determine the right thickness of insulation boards, you first need to know the average lambda value and the desired Rd value. It depends on your home, its year of construction, and the insulation standards in your area. For a standard house, an Rd value of 3.5 m²K/W for floor insulation is sufficient, while a higher Rd value (at least 6 m²K/W) is recommended for roofs and external walls.
Sample calculation for PIR boards and thickness of roof insulation
PIR boards have a high insulation value per centimetre. For example, a PIR board 10 cm thick has an Rd value of about 4.5 m²K/W. This makes PIR particularly suitable for applications where there is limited space, such as floors or roofs.
Factors affecting insulation board thickness, including lambda value
The thickness of insulation boards is determined by several factors, including:
- Rd value: the Rd value indicates the insulation value of the material. The higher the Rd value, the better the material insulates. PIR boards are known for their high Rd value compared to other insulation materials. For example, 10-cm PIR boards can achieve the same insulation value as 15-cm mineral wool. PUR and PIR are among the best insulating materials because of their low lambda value, allowing you to use relatively thin insulation but still achieve a good insulation value. We should emphasise that a minimum Rd value can be achieved with a thickness of 12 to 14 centimetres.
- Building regulations: the thickness of insulation must comply with local building regulations and energy performance standards. In many cases, these regulations require a minimum insulation thickness.
- Available space: especially in renovations, available space can be limited, which influences the choice of insulation thickness.
What is the best thickness for floor insulation?
A thickness between 6 and 12 cm is recommended for floor insulation, depending on the available space. Choose PIR boards because of their high insulation value per cm.
How thick should roof insulation be?
For pitched roofs, a thickness of 12 to 24 cm is recommended, while flat roofs require 14 to 20 cm to meet modern insulation standards. Good insulation improves comfort and reduces energy costs.
How do you determine the thickness of facade insulation?
External wall insulation often requires a thicker layer of insulation, between 10 and 16 cm, to meet today’s energy standards and minimise heat loss through the walls. Good insulation is essential in order to realise the benefits of insulation, such as increased comfort and lower energy costs.
