Frequently Asked Questions – PIR Insulation Boards

1. What Is a PIR Insulation Board?

A PIR insulation board is a modern thermal insulation material made from rigid polyisocyanurate foam. It offers excellent thermal insulation performance, low weight and high efficiency at a relatively small thickness.

PIR boards are used to insulate roofs, attics, walls, floors and ceilings in both residential and industrial buildings.

One of their greatest advantages is their low thermal conductivity (lambda, λ), which can be as low as 0.022 W/(m·K) for selected PIR boards. This makes it possible to achieve excellent thermal insulation without using thick insulation layers.

2. What Is the Difference Between PIR and PUR?

PIR (polyisocyanurate) and PUR (polyurethane) are related insulation materials that differ in their chemical structure and performance characteristics.

PIR boards generally offer greater thermal stability and more favourable behaviour at elevated temperatures than typical PUR foams.

When exposed to high temperatures, a charred layer may form on the surface of PIR. This can limit heat penetration into the deeper layers of the material and slow down further decomposition.

Both materials provide good thermal insulation, but PIR is often chosen for applications requiring rigid insulation with high thermal efficiency.

The selection of a specific product should take into account its declared performance characteristics and the requirements of the building element.

3. What Are PIR Insulation Boards Used For?

PIR boards are used for thermal insulation in buildings, helping reduce heat loss in winter and heat gain in summer.

Their most common applications include:

• Insulating pitched and flat roofs.
• Insulating habitable and non-habitable attics.
• Insulating external and internal walls.
• Insulating floors and floor structures.
• Insulating garages, workshops and utility buildings.
• Improving the thermal performance of existing buildings.

PIR boards are particularly useful where high thermal insulation performance is required but the available space for insulation is limited.

4. Is PIR Better Than EPS Insulation?

PIR boards generally provide better thermal insulation than standard expanded polystyrene (EPS), meaning a thinner layer can achieve a similar level of thermal resistance.

For example, 10 cm of PIR insulation with λ = 0.022 W/(m·K) provides approximately the same thermal resistance as 16 cm of EPS insulation with λ = 0.035 W/(m·K).

PIR is particularly useful where insulation space is limited, such as in attics, terraces and floors.

EPS is often less expensive to purchase. Therefore, when choosing between the two materials, it is worth comparing not only the material price but also the required insulation thickness, mechanical properties and total system cost.

5. Is PIR Better Than Mineral Wool?

PIR boards and mineral wool have different properties, so the best choice depends on the type of building and the required insulation performance.

PIR provides excellent thermal insulation at a smaller thickness. Mineral wool, on the other hand, offers favourable acoustic properties and is available in products with a reaction-to-fire classification of A1 or A2.

Lambda values are expressed in W/(m·K). The ranges are indicative.

If saving space while maintaining high thermal insulation performance is the main priority, PIR may be the more suitable option. Where non-combustibility or acoustic insulation is particularly important, mineral wool is worth considering.

6. What Is the Thermal Conductivity (Lambda) of PIR Boards?

The thermal conductivity coefficient, lambda (λ), indicates how effectively a material limits heat transfer. The lower the value, the better its insulating performance at the same thickness.

PIR boards typically achieve lambda values of approximately 0.022 to 0.027 W/(m·K), depending on the product, its facings and thickness.

For example, termPIR AL boards with aluminium facings may achieve a declared thermal conductivity of 0.022 W/(m·K).

Thanks to their low lambda value, PIR boards can reduce the thickness of the insulation layer compared with many traditional insulation materials.

When purchasing insulation, always check the declared λD value of the specific product.

7. Are PIR Boards Moisture-Resistant?

PIR boards have a predominantly closed-cell structure, which means that many products have low water absorption.

They can be used in various building assemblies, including areas exposed to increased humidity, provided that an appropriate insulation system is used.

However, moisture resistance does not mean complete waterproofing. PIR boards do not replace waterproofing membranes, and their joints and edges must be properly protected.

A well-designed PIR insulation system can help reduce the risk of condensation caused by cold building elements, but this requires the correct design of the entire layer arrangement.

8. How Long Do PIR Insulation Boards Last?

PIR boards are thermal insulation materials designed for long-term use. When correctly installed and used, they can retain their properties for many decades.

Their durability depends primarily on operating conditions, protection against moisture and UV radiation, and selecting a suitable product for the intended application.

Unlike materials that may settle in certain installation systems, rigid PIR boards retain their shape when used under appropriate conditions.

Properly installed PIR insulation does not require regular replacement simply because of its age. However, the exact service life and warranty conditions depend on the specific product and system.

9. Are PIR Insulation Boards Safe for Health?

PIR boards intended for construction applications can be used safely when properly installed and used according to the manufacturer’s instructions.

After manufacturing, they form a rigid insulation material suitable for appropriately designed building assemblies in residential and commercial buildings.

During cutting and installation, dust exposure should be minimised and recommended personal protective equipment should be used.

When selecting a product, check its technical documentation, declared properties and intended use. For internal applications, correct installation of the facing and finishing layers is also particularly important.

10. What Thickness of PIR Insulation Board Should You Choose?

The thickness of a PIR board should be matched to the type of building element, required thermal insulation performance and properties of the chosen material.

For a thermal conductivity of λ = 0.022 W/(m·K), different thicknesses provide the following thermal resistance values:

R is expressed in m²·K/W. Values are calculated for λ = 0.022 W/(m·K).

The thicker the PIR insulation layer, the greater its thermal resistance and the lower the heat loss through the insulation.

When choosing a thickness, consider the U-value of the entire building element rather than just the thickness of the insulation board.

11. How Much PIR Insulation Is Equivalent to 10 cm of EPS?

To achieve thermal resistance comparable to 10 cm of standard EPS insulation with λ = 0.035 W/(m·K), approximately 6.3 cm of PIR insulation with λ = 0.022 W/(m·K) is sufficient.

In practice, a 70 mm PIR board can be used, providing slightly higher thermal resistance than the specified 100 mm EPS layer.

This means saving approximately 3 cm of insulation thickness, which can be particularly useful when insulating floors, attics and walls from the inside.

This comparison concerns the insulation layers themselves and assumes the specified lambda values.

12. How Much PIR Insulation Is Equivalent to 15 cm of EPS?

In terms of thermal resistance, 15 cm of EPS insulation with λ = 0.035 W/(m·K) corresponds to approximately 9.4 cm of PIR insulation with λ = 0.022 W/(m·K).

In practice, a 100 mm PIR board can be a suitable equivalent.

R is expressed in m²·K/W.

In this comparison, 100 mm PIR provides slightly better thermal insulation than 150 mm EPS while being 5 cm thinner.

13. How Much PIR Insulation Is Equivalent to 20 cm of EPS?

20 cm of EPS insulation with λ = 0.035 W/(m·K) corresponds to approximately 12.6 cm of PIR insulation with λ = 0.022 W/(m·K).

To achieve at least similar thermal resistance, a 130 mm PIR board can be considered if this thickness is available in the selected system.

R is expressed in m²·K/W.

Using PIR can reduce insulation thickness by approximately 7 cm while maintaining comparable thermal resistance.

14. Is 50 mm PIR Insulation Enough?

A 50 mm PIR board can provide an effective insulation layer, but whether it is sufficient depends on the type of building element and the building’s thermal requirements.

At λ = 0.022 W/(m·K), a 50 mm PIR board provides a thermal resistance of approximately 2.27 m²·K/W.

This thickness can be used, for example, as an additional insulation layer in an attic, wall, ceiling or garage.

In heated residential buildings, 50 mm PIR is generally not sufficient as the only insulation layer for a roof or external wall.

The required thickness should be determined by calculating the U-value of the entire building element.

15. Is 80 mm PIR Insulation Enough for an Attic?

An 80 mm PIR board with λ = 0.022 W/(m·K) provides a thermal resistance of approximately 3.64 m²·K/W.

It can be used as an additional attic insulation layer, for example beneath the rafters or in combination with insulation between the rafters.

In a heated residential attic, 80 mm PIR is generally insufficient as the only insulation layer to achieve the required U-value of 0.15 W/(m²·K) or lower.

The final thickness depends on the roof structure, other insulation layers and the effects of thermal bridges.

16. Is 100 mm PIR Insulation Enough for a Roof?

A 100 mm PIR board with λ = 0.022 W/(m·K) provides a thermal resistance of approximately 4.55 m²·K/W.

This thickness may work as part of a roof insulation system, but in heated residential buildings it is usually insufficient as the only thermal insulation layer.

For roofs above typical heated residential spaces in Poland, the maximum permitted U-value is 0.15 W/(m²·K).

In many systems, PIR boards with a thickness of approximately 150–160 mm or more are worth considering, depending on the complete roof construction.

Before selecting the material, thermal calculations should be carried out, taking into account all roof layers and thermal bridges.

17. What PIR Insulation Thickness Is Recommended for Floors?

The required thickness of PIR floor insulation depends on the building structure, substrate type, heating system and required thermal performance.

For λ = 0.022 W/(m·K), the indicative thermal resistance values are:

R is expressed in m²·K/W.

For ground floors in heated residential rooms in Poland, the maximum required U-value is generally 0.30 W/(m²·K).

When selecting PIR boards, consider not only thermal insulation performance but also compressive strength, expected floor loads and the requirements of the complete flooring system.

18. What PIR Insulation Thickness Is Recommended for Walls?

The thickness of PIR insulation for walls depends on the structural material, existing insulation and required thermal transmittance (U-value).

For typical external walls of heated residential buildings in Poland, the requirement is U ≤ 0.20 W/(m²·K).

A 100 mm PIR board with λ = 0.022 W/(m·K) provides a thermal resistance of approximately 4.55 m²·K/W and may be sufficient in certain wall constructions.

However, the final choice should be confirmed by thermal calculations for the entire wall assembly.

When insulating from the inside, the risk of water vapour condensation must also be considered, and the arrangement of layers should be designed accordingly.

19. How Do You Choose PIR Thickness to Meet Poland’s WT 2021 Requirements?

The thickness of PIR insulation boards should be selected so that the entire building element meets the applicable thermal insulation requirements.

For typical heated residential spaces in Poland, the maximum U-values are:

The required insulation thickness can initially be estimated using the formula:

R = d / λ

where R is thermal resistance, d is the material thickness in metres and λ is the thermal conductivity coefficient.

For example, a 150 mm PIR board with λ = 0.022 W/(m·K) provides a thermal resistance of approximately 6.82 m²·K/W.

However, the thermal resistance of the insulation alone does not establish compliance with WT 2021. Other layers, thermal bridges and relevant calculation corrections must also be considered.

20. Are PIR Boards Suitable for Roof Insulation?

Yes. PIR boards are widely used for insulating pitched and flat roofs in both residential and industrial construction.

Their main advantage is the ability to achieve high thermal insulation performance with a relatively small material thickness.

Depending on the roof type and system, PIR boards can be installed:

• Above the rafters.
• Below the rafters.
• Between the rafters, where the selected system permits this installation method.
• On flat roofs, beneath a suitable waterproofing system.

In pitched roofs, above-rafter PIR insulation can reduce thermal bridges associated with the timber roof structure.

For flat roofs, PIR boards must have appropriate mechanical strength and facings compatible with the planned roofing system.

Properly selected PIR boards can be used in roof assemblies that meet thermal insulation and fire safety requirements, including appropriately classified roof systems that do not contribute to fire spread (NRO under Polish regulations).

However, the NRO classification must apply to the specific tested roof assembly.