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Views: 0 Author: Site Editor Publish Time: 2025-01-17 Origin: Site
When it comes to improving energy efficiency in buildings, insulation plays a critical role. Among the many insulation materials available, PIR insulation boards stand out for their high performance and versatility. But one of the most frequently asked questions by homeowners, builders, and architects is: What thickness of PIR insulation do I need? The answer depends on a variety of factors, such as the part of the building being insulated, building regulations, and the desired thermal performance.
In this comprehensive guide, we'll explore the key factors that determine the thickness of PIR insulation boards, including their R-value and U-value, and provide specific recommendations for different applications like lofts, floors, roofs, and walls. We'll also highlight how PIR compares with other insulation materials to help you make an informed decision.
The R-value is a measure of thermal resistance. It tells you how well a material resists the transfer of heat. The higher the R-value, the better the insulation performance. For PIR insulation boards, the R-value is determined by the thickness of the board and the thermal conductivity (or lambda value) of the material.
Key points about R-values:
The R-value is expressed in m²K/W (square meter Kelvin per Watt).
The formula for R-value is:
R = Thickness (m) ÷ Thermal Conductivity (W/m·K).
PIR board has one of the best thermal conductivities of any insulation material, typically ranging from 0.021 to 0.026 W/m·K, which means it provides a high R-value even at relatively thin thicknesses. This makes PIR insulation boards an excellent choice for projects where space is limited.
For example, a 50mm PIR board with a thermal conductivity of 0.022 W/m·K offers an R-value of approximately 2.27 m²K/W. In comparison, other insulation materials like mineral wool or expanded polystyrene (EPS) would require greater thicknesses to achieve the same R-value.
While the R-value measures the performance of an individual material, the U-value measures the overall thermal performance of a building element (like a wall, floor, or roof). It incorporates all the layers of the construction, including insulation, plasterboard, and external finishes.
Key points about U-values:
The U-value is expressed in W/m²K (Watts per square meter Kelvin).
The lower the U-value, the better the thermal performance of the building element.
U-values are critical for meeting building regulations. For example, in the UK, the recommended U-value for walls in new builds is 0.18 W/m²K, while for roofs, it's 0.11 W/m²K.
The thickness of PIR insulation boards required will depend on the desired U-value and the specific construction type. For instance, achieving a U-value of 0.18 W/m²K in a cavity wall may require a different PIR board thickness than achieving the same U-value in a flat roof.
The required thickness of PIR insulation boards depends on where they are installed and the target U-value. Below, we'll break down the recommended thicknesses for common applications.
Loft insulation is one of the most effective ways to reduce heat loss in a building. PIR insulation boards can be used to insulate lofts either between or over the joists.
Key considerations:
Building regulations in the UK recommend a U-value of 0.11 W/m²K for roofs, which typically requires around 270mm of mineral wool insulation.
However, since PIR boards are more efficient, you can achieve the same U-value with a much thinner layer.
Recommended thickness of PIR boards for lofts:
| U-value Target (W/m²K) | PIR Thickness (mm) |
|---|---|
| 0.11 | 120-140 |
| 0.15 | 100-110 |
| 0.18 | 80-90 |
Insulating floors can significantly reduce heat loss, particularly in ground-floor spaces. PIR insulation boards are ideal for floor insulation because of their high compressive strength and low thickness requirements.
Key considerations:
The U-value target for floors in new builds is typically 0.18 W/m²K, though this can vary depending on local regulations.
PIR boards are often installed above a damp-proof membrane (DPM) or below screed.
Recommended thickness of PIR boards for floors:
| U-value Target (W/m²K) | PIR Thickness (mm) |
|---|---|
| 0.11 | 120-130 |
| 0.15 | 100-110 |
| 0.18 | 80-90 |
In pitched roofs, PIR insulation boards can be installed either between the rafters or over them, depending on the design.
Key considerations:
The U-value target for pitched roofs is typically 0.13-0.18 W/m²K.
Installing PIR boards over rafters (warm roof construction) provides a continuous layer of insulation, minimizing thermal bridging.
Recommended thickness of PIR boards for pitched roofs:
| U-value Target (W/m²K) | PIR Thickness (mm) |
|---|---|
| 0.13 | 140-160 |
| 0.15 | 120-140 |
| 0.18 | 100-120 |
Flat roofs are particularly prone to heat loss, making insulation essential. PIR insulation boards are the most common choice for flat roofs due to their high performance and lightweight properties.
Key considerations:
The U-value target for flat roofs is typically 0.18 W/m²K.
Insulation is usually installed above the waterproof membrane (warm roof design).
Recommended thickness of PIR boards for flat roofs:
| U-value Target (W/m²K) | PIR Thickness (mm) |
|---|---|
| 0.11 | 140-160 |
| 0.15 | 120-140 |
| 0.18 | 100-110 |
Cavity wall insulation involves filling the gap between the inner and outer walls with an insulating material. PIR boards are often used in partial-fill cavity wall insulation systems.
Key considerations:
The U-value target for walls is typically 0.18 W/m²K.
The thickness of the PIR board used will depend on the width of the cavity.
Recommended thickness of PIR boards for cavity walls:
| U-value Target (W/m²K) | PIR Thickness (mm) |
|---|---|
| 0.18 | 90-100 |
| 0.22 | 80-90 |
PIR insulation boards are an exceptional choice for achieving high levels of thermal performance with minimal thickness. Their low thermal conductivity means that less material is needed to meet building regulations compared to other insulation types. However, the required thickness will vary depending on the specific application, the desired U-value, and the construction type.
By understanding the differences between R-values and U-values, and how they relate to insulation thickness, you can make informed decisions about your insulation needs. Whether you're insulating a loft, floor, roof, or wall, PIR boards offer a space-saving and efficient solution that helps reduce energy costs and improve comfort.
1. What is a PIR insulation board?
A PIR insulation board is a rigid foam insulation material made from polyisocyanurate. It has a high thermal performance, making it ideal for various applications like walls, roofs, and floors.
2. How does PIR insulation compare to other materials?
PIR boards have a lower thermal conductivity than materials like mineral wool or EPS, meaning they provide better insulation with less thickness.
3. Can I use PIR insulation for external walls?
Yes, PIR boards can be used in external wall insulation systems, either as part of a cavity wall or in an external render system.
4. Are PIR boards moisture-resistant?
Yes, PIR insulation boards are highly resistant to moisture, making them suitable for applications like floors and roofs.
5. How do I calculate the thickness of PIR insulation required?
To calculate the thickness, you need to know the target U-value and the thermal conductivity of the PIR board. Consult the product's technical datasheet for specific details.
